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Climate change mitigation in cities: a systematic scoping of case studies

Mahendra Sethi 1,2 , William Lamb 2,3 , Jan Minx 2,4 and Felix Creutzig 1,2

Published 26 August 2020 • © 2020 The Author(s). Published by IOP Publishing Ltd Environmental Research Letters , Volume 15 , Number 9 Focus on Systematizing and Upscaling Urban Solutions for Climate Change Mitigation Citation Mahendra Sethi et al 2020 Environ. Res. Lett. 15 093008 DOI 10.1088/1748-9326/ab99ff

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1 Technical University of Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany

2 Mercator Research Institute on Global Commons and Climate Change, Torgauer Straße 12–15, EUREF Campus #19, 10829, Berlin, Germany

3 School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom

4 Priestley International Centre for Climate, University of Leeds, Leeds LS2 9JT, United Kingdom

Mahendra Sethi https://orcid.org/0000-0003-1065-5484

William Lamb https://orcid.org/0000-0003-3273-7878

Jan Minx https://orcid.org/0000-0002-2862-0178

Felix Creutzig https://orcid.org/0000-0002-5710-3348

• Received 18 February 2019
• Accepted 5 June 2020
• Published 26 August 2020

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Method : Single-anonymous Revisions: 3 Screened for originality? Yes

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A growing number of researchers and stakeholders have started to address climate change from the bottom up: by devising scientific models, climate plans, low-carbon strategies and development policies with climate co-benefits. Little is known about the comparative characteristics of these interventions, including their relative efficacy, potentials and emissions reductions. A more systematic understanding is required to delineate the urban mitigation space and inform decision-making. Here, we utilize bibliometric methods and machine learning to meta-analyze 5635 urban case studies of climate change mitigation. We identify 867 studies that explicitly consider technological or policy instruments, and categorize these studies according to policy type, sector, abatement potential, and socio-technological composition to obtain a first heuristic of what is their pattern. Overall, we find 41 different urban solutions with an average GHG abatement potential ranging from 5.2% to 105%, most of them clustering in the building and transport sectors. More than three-fourth of the solutions are on demand side. Less than 10% of all studies were ex-post policy evaluations. Our results demonstrate that technology-oriented interventions in urban waste, transport and energy sectors have the highest marginal abatement potential, while system-wide interventions, e.g. urban form related measures have lower marginal abatement potential but wider scope. We also demonstrate that integrating measures across urban sectors realizes synergies in GHG emission reductions. Our results reveal a rich evidence of techno-policy choices that together enlarge the urban solutions space and augment actions currently considered in global assessments of climate mitigation.

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1. Introduction: summary of evidence gap and research question

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The role of urban areas in contributing to climate mitigation and adaptation, global sustainable development goals (SDG) and the New Urban Agenda (NUA) is undisputed (UN Habitat 2011 , IPCC 2014 , 2018 , UN-United Nations 2015 , 2016 ). In the last few decades, a growing number of cities and local governments have teamed-up to combat climate change from the bottom up: hundreds have developed and are implementing local climate action plans (UN Habitat 2015 , Deetjen et al 2018 , Reckien et al 2018 , C40 Cities 2019 , WRI 2019 ). Yet, the contribution of urban climate solutions to climate change mitigation remains poorly understood: we still have very little understanding of how well urban policy interventions work, under what conditions and why (Grubler et al 2012 , Revi et al 2014 , Seto et al 2014 , Rosenzweig et al 2015 , Minx et al 2017 , Bai et al 2018 ). The urban climate change literature is paved with individual case studies challenging our ability to maintain an oversight of new developments (Lamb et al 2019 ). Case-study evidence is used primarily in an anecdotal fashion leaving a large, untapped potential for systematic learning on urban climate solutions. There are at least two paths to upscale and systematize the study of urban-scale climate solutions (Creutzig et al 2019 ). One is data driven starting with city-scale datasets being combined with harmonized remote sensing or other land-use information to develop data-based typologies of cities and climate change (e.g. Creutzig et al 2015 , Baiocchi et al 2015 , Ahmed et al 2019 , Nangini et al 2019 , Solecki et al 2015 ). The other is evidence-driven synthesis starting with case studies to systematically compare and aggregate policy insights (Broto and Bulkeley 2013 , Kivimaa et al 2015 , Reckien et al 2018 ). Both can be eventually combined to match experience from case studies to urban drivers of energy use and climate change (Lamb et al 2019 , Creutzig et al 2019 ).

What useful information can one derive from urban case studies? A systematic scoping of these studies can reveal a spectrum of urban solutions available to policy makers—instruments, targeted sectors, expected (or documented) mitigation potentials, and social outcomes. This information could support fast learning among peer-cities particularly those responsible for large segments of global greenhouse gas (GHG) emissions (Creutzig et al 2015 , Baiocchi et al 2015 , Lamb et al 2018 ). In particular, there is a pressing need to identify solutions for smaller and medium sized cities, that too in developing countries. These cities will host the majority of future population growth, energy consumption and GHG emissions yet are most underequipped in financial and human resources to study and implement local climate action (GEA 2012 , Seto et al 2014 , Sethi and Puppim de Oliveira 2015 ).

A growing number of studies model climate mitigation potential in cities. Emission inventory exercises identify key priority areas for urban mitigation across multiple sectors—particularly when carried out in a comparative context (e.g. ICLEI 2009 , Kennedy et al 2009 , Chavez and Ramaswami 2013 ). For mid- and large- n samples of city inventories, parametric and non-parametric statistical approaches explain variations in urban CO 2 /GHG emissions due to socio-demographics, industrial structure, urban form, local geography and climatic conditions (Brown et al 2008 , Glaeser and Kahn 2010, Minx et al 2013 , Baiocchi et al 2015 ). Further refining such analysis, Creutzig et al ( 2015 ) use hierarchical regression-tree to endogenously cluster cities according to their GHG emission drivers and to estimate a global urban mitigation wedge. These studies are assimilative explorations into key drivers and thus potential areas to focus mitigation initiatives on, but they do not identify city-specific policy options that are directly available to urban policymakers.

Other studies have studied the ambition, focus, and regional distribution of urban climate actions (Broto and Bulkeley 2013 , Reckien et al 2014 , 2018 ). Yet, these studies abstract away from specific options and fall short of evaluating actual policy performance. As such, policy learning remains limited and insights are not actionable. This contrasts with a wealth of urban mitigation case studies available in the scientific literature (Lamb et al 2019 ) that offers the opportunity to systematically review this more granular evidence base and learn from experiences in pursuing technological solutions and urban policy instruments. We acknowledge the difficulties of such an undertaking, with inherent inconsistencies in methods, system boundaries, available data and desired outputs (Seto et al 2014 , Sethi 2017 ). Yet, in the absence of comprehensive and consistent evidence, working towards an initial heuristic for the urban climate solution space is a justifiable goal.

In this research, we apply a systematic scoping review methodology. A scoping review is guided by principles of transparency and reproducibility that follow a clear methodological protocol to analyse quantitative, qualitative or mixed evidence found in the scientific literature (Arksey and O'Malley 2005 ). As in other systematic evidence-synthesis approaches, it involves the following steps: (a) clearly defining the research question; (b) systematically searching defined literature databases for a defined time period; (c) justifying and making a transparent selection of the literature; (d) assessing the quality of the selected evidence; and (e) synthesizing the evidence based on a clear and transparent method (Berrang-Ford et al 2015 , Minx et al 2017 ). In this scoping review, we assess the urban case study literature pursuing four distinct, but inter-related research objectives: (1) to map global urban interventions, capturing the contributions across different mitigation sub-sectors, (2) to survey key urban mitigation solutions being practiced along with their GHG abatement potential, (3) to examine ex-post policy studies for specificity of opted policies and their governing mode, and (4) to capture trends and focus of the latest research and innovations in urban climate mitigation. In section 2 , we outline our review methodology, and in section 3 we describe analytical findings. In section 4 , we conclude with recommendations for future research.

2. Methodology

Climate change assessments, such as those by the Intergovernmental Panel on Climate Change (IPCC), gained status for evidence-based scientific policy advice. The progress in international climate governance would have not been possible without systematic learning in the scientific community. However, there has been little systematic learning on climate solutions from ex-post evidence. Systematic review methods as developed in health and educational sciences provide an adequate methodological toolkit for such learning, but have generally been neglected in climate and energy research. Only recently, a growing number of researchers have started applying systematic review methods in climate studies more widely (Berrang-Ford et al 2015 , Fuss et al 2018 , Minx et al 2018 , Nemet et al 2018 ). Such systematic reviews are challenging in that they deal with the vast and fast-growing evidence base. We call this new phenomenon 'big literature': resource-intensive systematic review methods are pushed to the brinks of feasibility (Minx et al 2017 ). Employing data science methods to assist during the systematic review process by lifting the burden of some of the most repetitive and resource-intensive tasks from human reviewers is a promising and crucial development in the field of evidence synthesis (Minx et al 2017 , Westgate et al 2018 , Nakagawa et al 2019 ).

In a recent experiment, Lamb et al ( 2019 ) apply data science and unsupervised machine learning (ML) methods to automatically map out the case study landscape on urban climate change mitigation. Rather than dozens or hundreds of case studies as analysed by urban climate change assessments (Seto et al 2014 ), it identifies more than 4000 cases, covering a broad range of topics from emission accounting to technology studies to scenario analysis to policy impact evaluations. We update this with an expanded database of 20 166 studies for our systematic review of technology and policy options in urban climate change mitigation. The detailed methodology for the review process is explained in annex 1 (available online at stacks.iop.org/ERL/15/094067/mmedia ) and summarized as a flowchart in figure 1 . As a first step, we search the Web of Science and Scopus with a broad query comprising synonyms for climate mitigation and urban policies (annex 1.1, table A1). We filter the resulting documents using a data bank of worldwide city names, resulting into 5635 case studies that mention cities in their title and abstracts. Next, we read a random sample of 250 papers to develop inclusion and exclusion criteria for our scoping review (annex 1.2, table A2). With the developed exclusion and inclusion criteria we then tested inclusion/exclusion for a further set of 200 papers (annex 1.2, table A3). We then used the coded papers as input for a supervised machine learning algorithm that calculates relevance rates for the remaining 5635 case studies. For the final review, we include all studies with a relevance rate of 0.6 or higher, resulting in 867 papers (annex 1.3). In the final stage, post-ML analysis and synthesis involves systematic coding and tagging of the content (annex 1.4) finding that 644 out of the 867 studies matched our inclusion criteria followed by an array of results. Section 3 reports our analytical findings sequentially for each research objective.

Figure 1.  The research methodology, scoping of case studies (in numbers) and results reporting for each objective.

3. Results discussion

The systematic review of case study literature leads to the following major outcomes: ( 3.1 ) Mapping of urban interventions globally, capturing the contribution of different mitigation sectors; ( 3.2 ) Exploring key urban mitigation solutions being practiced along with their GHG abatement potential; ( 3.3 ) Examining ex-post policy studies for specificity of policy mode opted in different urban mitigation solutions; ( 3.4 ) Identifying the focus of recent trends and innovations in urban climate mitigation.

3.1. Mapping of literature for GHG mitigation sectors

We map case study articles to the following sectors: buildings, energy, transport, waste; agriculture, forestry and other land uses (AFOLU) and industry. In the paper set, we find 548 studies focusing on a single sector, with buildings (249) and transport (148) most frequently investigated. There are 77 studies scrutinizing two sectors simulteneously, most often building and energy (21). A total of 19 studies cover 3 or more sectors (figure 1 , details in annex 2). Visualizing the intensity pattern of sectoral-interactions using a chord diagram (figure 2 - left) reveals a notable paucity of evidence observed between buildings–waste, industry- AFOLU/land, industry-waste and transport-industry sectors. Systematic reviews can be prone to inaccuracy in reporting if left unchecked for consistency of results. We hence hand-checked the relevance of post-ML results and validated these against the tested precision level (annex 3).

Figure 2.  Distribution of urban climate solutions- all (left) & ex-post policy (right), across different sectors. Source: Authors. The graphic demonstrates that volume and cross-connectivity between sectors for ex-post policy studies is significantly less in proportion to the entire urban climate solutions literature.

3.2. Key urban mitigation solutions and their mitigation potential

An in-depth analysis of 644 studies reveals several urban mitigation solutions evident across the six GHG mitigation sectors (figure 1 ). The most frequently identified interventions are demand-side management solutions that includes peak shaving or shifting (65 evidences), followed by energy efficiency (EE) measures (52), retrofitting a building completely (43), installing solar PV and PVT (43), integrated planning (41), fuel or technology shift (33), car free city (33), electric mobility (31), travel demand management (TDM) measures (26), biomass, bio-diesel, biomass gasification, ethanol production (26), waste to energy solutions (25), thermal insulation (23), public transport (22), urban form, design and planning (21), cool roofs (19), life-cycle assessments (19) and transit oriented development (18). Intrestingly, relatively ordinary, inexpensive and low-tech solutions e.g. water system efficiencies (12), mixed landuse (9), composting (7), walkability (5), non-motorised transport (4), greening/afforestation (4), parking management (3), and urban agriculture (2) find little evidence in case study literature.

Only 88 case studies across 46 solution typolgies provide quantitative data to estimate GHG abatement potential. Some cities like Vancouver, New York, Toronto, San Fransciso, London, Barcelona, Turin, Beijing, Tokyo, etc provide multiple studies in urban mitigation. These report results either as GHG mitigation, energy reduction or cost savings (essentially GHG abatement potential), all in percentage-points and ennumerated in annex 4. This enables us to evaluate relative opportunities offerred by these solutions. Out of 46 urban mitigation solutions, quantifiable data was available for only 41. We rank demand-side potential for climate change mitigation (figure 3 ), benchmarked against business-as-usual scenario (BAU) as defined in each individual study. Different studies can have a range of baselines and end-points for reporting percentage GHG reductions (Erickson and Broekhoff 2017 ). In this analysis, we consider studies with baseline ranging from 1979 to 2019 and report results on the basis of project vs non-project percentage variation, drawing inter-sectoral comparisons as has been the method in the recent AR5 (IPCC 2014 , p 92). Several variables contextualize the results:

• (a)   Geographical origin: Many studies originated in Europe and China (annex 5). The most notable heterogeneity is evident in cool-roof performance because of location. Cool roofs are less often deployed in higher latitudes (13%) and more frequently in lower latitudes (28%). Other climate policies are deployed similarly across geographic regions.
• (b)   Sector contributions: On an average, the highest mitigation values are observed in three chief sectors: buildings with net-zero emission buildings (NZEB) 105% (Wilkinson and Boehm 2005 ), transportation with E-mobility 94% (Van Duin, et al 2013, Prata et al 2015) & Waste with waste to energy 87% (Mustafa et al 2013 ). While a combination of certain sectors may give relatively moderate to low GHG abatement, in certain urban contexts these can potentially offer low-hanging fruits for decision makers and local bodies to deliberate on, especially if the scope and scale are controlled (explained below #5).
• (c)   Heterogeneity within an urban solution: The 41 urban solutions are categorized based on their techno-policy distinctiveness to be implemented as practical solutions within an urban setting. A particular solution could invariably include multiple sub-variants of technology. For example, 'electric mobility' includes studies examining full replacement of cars by e-bikes, replacement of individual conventional cars with light duty electric vehicles (EVs), and adoption of EVs in freight—all of which are different in terms of technology and their efficacy. To reflect policy relevance, we have segregated their use in public and private modes. For details see annex 4.
• (d)   Technological and social initiatives : Technology based interventions are more prevalent. Out of 41 urban climate solutions, 33 (80.5%) are technologically driven, 3 (7.31%) are society oriented and the remaining 5 interventions are technological and social. More than two thirds of solutions are on the demand-side, and less than one third on the supply side (figure 3 ).
• (e)   Scope (system boundaries) & Scalar effect : The scale of intervention controls mitigation potential at two levels. The first is at the systems level- with all things being equal, interventions with smaller absolute scope demonstrate greater marginal mitigation potential than more system-wide interventions. For instance, NZEB (105%) against retrofitting a precinct (50%) or sustainable urban form (23%) in the city. Similarly, waste to energy in a plant (87%) against integrated waste management (58%) in the city, or mitigation opportunities in public transportation system (51%) against complete TDM (27%) in the city. This information is crucial for local authorities and stakeholders to initiate policy action with small-scale manageable projects having high marginal impact, while simultaneously pursuing more system-wide approaches.

Figure 3.  Rank Diagram of average GHG abatement potential from BAU (in %) and categorization into technological and social-oriented solutions, and demand vs supply categories.

A further disaggregation of sectors for quantifiable solutions, in decreasing order of their average mitigation potential, indicates the following-

Waste (50%): The GHG abatement potential of 5 climate solutions in waste sector range from biomass, biomass gasification (21%) to waste to energy (87%) in project versus non-project scenario. The surge in climate mitigation potential with rising up the technology ladder are evident. On an average, the waste sector offers the maximum demand side GHG mitigation potential in cities with the most concentrated yet least number of measures, thus offering a low-hanging fruit to urban local bodies.

Transport (43%): The mitigation potential of 8 climate solutions in energy sector range from intelligent transportation system (ITS) (20%) to EV and hybrid EV (HEV) in public & private vehicles (94%), with the average being 43%. The results indicate that GHG savings from travel demand management, fuel shift and ITS plateau at 28%, beyond which deep mitigation can be attained only through pan-city expansion of public transportation system, particularly by introducing EV/HEVs. Most of these interventions are supply-driven and controlled by urban transport authorities and local governments.

Energy (38%): The mitigation potential of 14 climate solutions in energy sector range from expanding district heating/cooling (12%) to PV thermal and solar tri-generation (CPVT) solution (73%), with the average being 38%. The energy sector demonstrates a range of solutions, a lot of which are associated with the supply-side than in any other sector. These are district heating/cooling, PV thermal, solar tri-generation CPVT, etc though few demand side energy measure to reduce GHGs are also observed, like EE & conservation measures, consumer demand response models, optimization models in modulating energy consumption at local (community) level, in water systems, heat pumps, street-lighting optimizing energy demand with solar substitution and/or energy storage, demand adjustment for district heating, etc.

Buildings (35%): The relative mitigation potential of 13 climate solutions in building sector ranges from cool roof/facade, roof garden in higher latitudes (13%) to NZEB, carbon neutral building (105%), averaging 35% with all other variables being the same. Excluding NZEB, the mitigation potential in this subsector limits at 50% with building retrofit. The double savings in NZEB against retrofit signifies substantial untapped mitigation potential in creating new infrastructure or redeveloping old precincts to NZEB district than pursuing incremental retrofits.

Conventional insulation and thermal comfort solutions incorporated into the building during construction are twice more effective in reducing energy demand than operational/performance measures like automated building information system (BIS), intelligent controls, smart meters, etc or user driven EE measures. At the same time, urban bodies need to utilize these results with prudence. They should keep in view that the gross mitigation potential of NZEB versus retrofits would depend on multiple local factors, for instance (a) the relative prevalence of new buildings vs. old building stock; (b) how you locally define or interpret 'retrofitting'; and (c) relative cost-effectiveness of each solution, amongst others.

AFOLU (5.2%): There is o nly one urban solution- afforestation/greening with a mitigation potential of around 5%.

3.3. Review of ex-post policy studies

One of the key aims of this research is to examine ex-post policy studies for specificity of policy-governance instruments opted in different urban mitigation solutions. Firstly, only 73 (8.5%) out of 867 cases are ex-post policy studies, the most abundant in the buildings sector (26), followed by transport (16), energy (7), waste (5) and AFOLU/land (2). As the chord diagram of these evidences show (figure 2 - right), there are few cases observed in the nexus of buildings-energy (5), buildings and AFOLU/land (4), transport and AFOLU/land (2) while only seven urban solutions span through multiple sectors. The results suggest that the industry and waste sectors are most isolated and need integration with the rest of urban functions through innovations and policy convergence, to accrue greater GHG mitigation and climate co-benefits. Upon tagging these cases in accordance to four normative policy-governance modes, including overlapping (annex 6), we find that most of the urban solutions conform to enabling measures (46), regulatory instruments (45), voluntary, behavioural, awareness & education measures (37), followed by market/economic interventions (35). The following key observations emerge:

• (a)   There is a pre-occupancy of regulatory instruments that rely on legislations, standards/codes, certifications, etc across almost all GHG mitigation sectors, frequently observed in buildings and transport sector.
• (b)   Enabling and voluntary measures are not at all observed in waste sector, substantiating its isolation in urban GHG mitigation.
• (c)   There are only two evidences where all policy instruments are simultaneously employed in urban climate solutions. The case of Toronto highlights a mix-methods approach combining infrastructure provision, public acceptance, industry participation, regulating gasoline prices, tax incentives, subsidies for expanding EVs (Ing 2011 ). Also, local authorities like Leicester demonstrate different stakeholders can use multiple benefits approach with energy savings, job creation and community engagement to proactively meet national carbon reduction targets (Lemon et al 2015 ).

Surprisingly, initiatives such as car free cities, Fridays for future, odd–even car days, and congestion charges that capture active public interest, participation and media attention are missing in peer-reviewed scientific literature that we sampled. That contrasts with the high potential of transport-related lifestyle solutions to reduce individual carbon footprints (Ivanova et al 2020 ). A key reason might be that many urban-scale transport policies are primarily motivated by local concerns, such as congestion, air pollution, and quality of life, and thus may not occur in our literature data base. Secondly, policies need to be evaluated in terms of their relative effectiveness. For instance, in building projects, total renovation may not be optimal in all cases, while zero-cost measures like information campaigns could produce significant performance improvement (Pombo et al 2019, Calero et al 2018 ). Similarly, a better knowledge & propagation of energy codes, especially during early planning stage can have positive implications (Andrews et al 2016 ). Other effective intervention in the building sector include cap and trade for building energy emissions on lines of Tokyo (Nishida et al 2016 ), provision of incentives & subsidies, sustainable business models, focusing on thermal envelope system (than merely lighting); capacity building efforts and education campaigns, using of land-use planning and development approvals to expand green building market (Hou et al 2016 , Mellross and Fraser 2012 ).

For urban energy solutions, supply-side policies can be more effective if accompanied by participatory measures, as in Leicester, UK that simultaneously created jobs and engage communities in demand optimization (Lemon et al 2015 ). While technological solutions like solar PV accrue 30% cost savings (VanGeet et al 2008 ), yet complementary smart tariffication measures provide monetary incentives to households and motivate them to change their energy habits too (Kendel and Lazaric 2015 ). This certainly necessitates a greater role for enabling and voluntary modes of governance in supporting regulatory measures in urban mitigation.

Ex-post policies in the transportation sector further validate that demand-side interventions are indispensable for urban climate mitigation. For e.g. despite provisioning EV fleet in public transport in Jinhua, there is still an energy saving potential of 6.21% by optimizing departure time interval in line 1, with the same level of service (Wang et al 2017 ). Area traffic and parking restrictions with fuel taxation have substantial benefits in Athens (Goulas et al 2001 ), despite prevailing supply-side fuel efficiency norms. For significant outcomes, municipal plans should provide facilities that encourage increased use of transportation alternatives (walking, cycling, transit, etc.), that promote efficient vehicles and fuels (City of Vancouver 2005), enable enhanced involvement of people towards sustainable travel behaviour change as evident through holding the Big Green Commuter Challenge in Portsmouth City (Wall et al 2017 ), greater public transit use as in the case of Halifax, Moncton and Saint John in Canada (Gordon 2004 ), and adoption of smart parking system in London (Peng et al 2017 b).

Ex-post policy evaluation in AFOLU/land demonstrates that expanding of park area was the most appropriate initiative when considering both its effectiveness in reducing emissions, and its implementation cost in Bangkok (Kiewchaum et al 2017 ). In case of waste sector, different local conditions and waste composition were known to influence the choice of solution- landfill, incineration and composting (Assamoi and Lawryshyn 2012 , Hutton et al 2013 ). Urban mitigation across multiple sectors is scarce and spans across buildings, energy & transport. It involves technologies used for demand-side management that include natural-gas-based residential and commercial building heat pumps and chillers, cooking and water heating appliances developed for restaurant applications, and automobiles, buses, and trucks that use natural gas instead of gasoline (Wang et al 1995 ). These predominantly hinge on fuel-shift based rapid efforts or building-retrofit related sustained efforts, yet with significant health impacts (Tuomisto et al 2015 ).

In addition to the above cited evidence, there are certain plausible cross-cutting mitigation interventions viz. (a) Municipal waste-industry: demonstration of circular economy, biogas digestion, biomethanation & CO 2 e certificates, (b) AFOLU/land and waste: landfill site restoration to expand green cover and GHG mitigation, (c) Energy-transport: Instruments for bulk-purchase of green energy by transport companies, (d) Building-energy: Power purchase agreements between renewable energy plants, regional power grid, local electricity distribution companies on one end and townships, special zones, municipal councils, residential communities including prosumers on the other, and last but not the least (e) Ecocity/smart city developments: Integrated planned solutions encompassing solar PV, building EE measures, E-mobility, WTE and/or other combinations of the above interventions.

3.4. Recent trends, focus and innovations in urban mitigation

The past few years have witnessed advances in models, technologies and policies for climate urban mitigation, spanning all major GHG sectors except industry and AFOLU/land (table 1 ). Innovations advanced in the building sector (real time BIS, smart controls, roof-integrated solar technologies, efficient cooling & heating), albeit there is little evidence in their policy application. There is considerable use of technology in urban energy through heat pumps, solar PV, energy storage solutions, biomass gasification and energy-recovery demonstrator in district-heating. Meanwhile, policy innovations utilize community energy plans for utility-scale wind turbines, hybrid renewables and measures to re-evaluate national and local energy-efficiency design standards. There is fair mix of research, technological solutions and policy application evident in the transportation too. Complex computational models are built into apps, storage devices, breaking energy, and hybrid-fuel platforms supported by policy studies that optimize travel demand, improve street design, and strategize integrated and low-carbon transport planning. Other than EV/HEV, most of these measures enable incremental changes with no significant breakthrough from the status quo. The urban waste sector is well posited with research on life cycle assessment (LCA) of waste materials, analyzing optimal mix of different treatment and disposal technologies as well WTE applications. In addition, cross-sectoral interventions are experimenting with modelling & technologies in building-energy sectors (smart cities, green districts), land-transport related emissions as well as mechanisms to integrate climate goals with city master plans and setting up of demonstration projects. However, the cross-sectoral projects are few and need up-scaling to include non-contributing sectors. Also, policy innovations in unique sectors require expansion to apply models and technologies showing positive results for GHG mitigation.

Table 1.  Recent research in urban innovative models, technologies & policy solutions. For abbreviations, see notes at the bottom.

Notes: CO 2 : Carbon dioxide, DH: District heating, EV: Electric vehicles, GIS: Geographic information system, ITS: Intelligent transportation system, LU: landuse, RE: Renewable energy, SWM: Solid waste management, WTE: Waste to energy. For detailed tabulation see annex 7

4. Conclusion and recommendations

4.1. urban mitigation overwhelmingly presents demand-side solutions, yet it is still unsaturated.

Out of 41 quantifiable urban solutions, 33 (80.5%) exhibit demand-side interventions. Our findings support the prevailing literature (Lamb et al 2018 , Creutzig et al 2019 ) that topics like TDM, BEE, urban form, waste management dominate urban climate landscape, with irrefutably measureable evidence on the available mitigation choices and their relative efficacy. Our research pin-points technological and policy options and their GHG potential. For instance, most ex-post policy studies and current experiments are concentrated in the buildings and transport sectors, followed by energy and waste. The dearth of evidence in carbon sequestration initiatives indicates that (a) this topic is understudied in the urban literature, and/or that (b) cities designate insufficient importance to urban greening. However, most 'forward looking' studies (with futuristic scenarios) primarily deal with supply-side technologies in energy, CO 2 emission accounting, transportation and air-pollution (Lamb et al 2018 ). Thus advancing research should focus more on unexplored demand optimizing technologies and policies in urban industries, land and other cross-sectoral activities.

4.2. In urban climate literature, mitigation options that are frequency studied are not necessarily those with highest potential

The study of how literature is organized is important but the first step in any systematic review process. An earlier study, Lamb et al ( 2018 ) uses frequency mapping, topical modelling, clustering and bibliographic coupling networks to check representation of topics across sectors, time and geographical space. Yet, the meta-analysis of empirical and quantifiable data from global case studies is imperative for an informed decision-making. Comparing the results of both highlights some vital differences in representation and efficacy of urban climate solutions worldwide (figure 4 ). This bears vital inputs to agencies like IPCC, IEA/OECD that are now heavily relying on methodical reviews of case study literature for Assessment Report (AR6), Global Energy Outlooks, etc that (a) urban climate literature is still inadequately represented by technological and policy interventions that can effectively reduce or offset GHGs, and (b) climate solutions less frequently investigated in urban case studies (such as EVs that are typically addressed at national level transport policy) may nonetheless help cities to effectively address the 1.5 °C climate challenge.

Figure 4.  Comparison of key urban interventions for their marginal topic distribution results against their GHG abatement potential, in global case study literature. It is notable that solutions with high topical modelling (4.5%–9.7%) in literature like planning and governance, energy efficiency in buildings, travel demand management, urban form show a relatively lower demand-sensitivity (23%–27%) towards climate mitigation. Contrarily, solutions with lower topical representation (2.7%–4.4%) like integrated waste management, public transport, thermally insulated buildings, electric vehicles, transport provisioning show relatively higher climate mitigation potentials in the range of 47%–62%.

4.3. Technology coupling and synergistic interventions can upscale urban mitigation

Disruptive and synergetic technologies demonstrate that when it comes to GHG mitigation potential, the whole is greater than the sum of its parts (see figure 5 ). Out of 41 urban climate solutions, 33 (80.5%) are technologically driven, 3 (7.31%) are social oriented and the remaining 5 are both technology and social interventions. The results are in line with a previous study (Broto and Bulkeley 2013 ), wherein 76% of all experiments were technological, while only 50% were social innovation. The small proportion of social initiatives in our study partially reflect our exclusion of adaptation measures (Broto and Bulkeley 2013 observed that social innovations are more common in adaptation, carbon sequestration and urban form initiatives). Nevertheless, the significance of combining technological and social experiments to expand and upscale mitigation efforts in urban systems cannot be ruled out.

Figure 5.  The resultant mitigation potential (in %) of combining two urban interventions is greater than the net sum of individual interventions. District heating/cooling expansion provides 12% mitigation potential and PV Solar technology yields 14%, their coupling has steeper mitigation cut (37%). Similarly, buildings energy efficiency measures (23%) and PV Solar (14%) in tandem yield 65% mitigation potential. In transportation, expanding of existing technologies in public transport (62%) & electric mobility in private vehicles (39%) if combined, multiply benefits to 94%.

4.4. Expanding extra-regulatory and non-governmental actions is imperative in local climate governance

Technology is necessary but not a sufficient element to deepen urban mitigation. The overview of policy-governance measures corroborates an active role of local governments in leading urban climate solutions, through regulations (60.8%) or through partnerships between private or non-governmental actors (62%). A comparison with Broto and Bulkeley (Broto and Bulkeley 2013 ) shows that there is a slight shift observed in these last few years, when local governments' self-regulatory actions (66%) significantly outscored enabling measures (47%). This highlights an expanding form of horizontal partnerships by city governments with local agencies during 2013–19. The review of ex-post studies underscores that a mix of market mechanisms, user incentives, subsidies, voluntary measures, etc in cooperation with non-governmental actors is crucial for local climate mitigation.

Our scoping review is limited in certain ways. For example, it encounters a lot of heterogeneity and variabilities in cases. The unavailability of consistent data makes it hard to account for costs of mitigation options. We expect costs to vary with situations, depending on availability and price of the concerned resources & technologies, their in-direct costs, socio-economic costs, trade-offs, etc. The above nuances need further exploration through a full-systematic review and ought to be reasonably assessed while applying results to develop concerted urban policies and projects in different country & local contexts. Nevertheless, the research findings bear significant implication in analysing the efficacy of diverse demand-side climate solutions that will have a special reporting in the next IPCC report (AR6). In addition, the following insights or takeaways would help evolve a scientific and evidence based sustainable urbanism envisioned under the global SDGs & NUA, particularly for societies with rapidly developing infrastructures:

• (a)   Epistemological: Urban climate research requires a fusion of disciplinary knowledge in order to better utilize quantitative and qualitative data on how cities could respond to global warming. This investigation demonstrates how systematic learning from ongoing research and ex-post studies is still underutilized. With growing urban data collection across the globe (for more see Creutzig et al 2019 ), our study further affirms the significance of investing and learning through systematic review of case study and ex-post evidence by exploiting big literature and machine learning.
• (b)   Innovating technologies: Equipped with the above theoretical advances, urban innovation labs need to focus towards fostering ideas and technologies that not only enhance EE, fuel shift, etc (incremental solutions), in addition to innovating decarbonisation solutions exhibiting high effectiveness (like NZEB, EV, TDM) fully recognizing the obvious and the most infrequent linkages in urban systems. This aligns with the resilient urban systems discourse where all interventions (incremental, transitional and transformational) are considered equally applicable (Pearson et al 2014 , Chelleri et al 2015 , Meerow et al 2016 ). Our research underscores that energy-transport (e-mobility by prosumers and energy savings from breaking), transport-waste (route planning etc.), industry-waste (waste minimization, recycling), industry-AFOLU (mandatory sequestration, cap & trade, carbon capture) are inter-linkages that future innovations and research funding should explore.
• (c)   Policy design: Our review demonstrates significant GHG mitigation from cross-sectoral policy initiatives. For example, projects generating rooftop solar energy for consumption in green homes as well as both public and private EVs (Sugar and Kennedy 2012 , Litjens et al 2018 ). Similarly, integrated waste management demonstrates both GHG mitigation from households and industries, as well as lowered local air-pollution at the city scale (Liamsanguan and Gheewala 2008 ). Urban strategies need to develop NZEB and retrofits in mix-land use districts where non-motorised mobility can generate multiple benefits of climate mitigation, ordered urban-planning, improved local environment and jobs. The good news is that most of these portfolios are a mandate of urban local governments. The mainstreaming of climate change into national policies (UN Habitat and UNESCAP 2018 ), particularly national-urban frameworks (Sethi and de Oliveira 2018 ) present a good opportunity for systematic analysis of sustainability and local development issues in developing context. It can guide urban agencies for the necessary capacity building, financial support, performance targets, peer-competition and opportunities to be seen as acting decisively on environmental challenges.
• (d)   Societal applications: Soft infrastructures, such as habits and norms, shape behavior and consequently offer potential to reduce energy demand and GHGs (Hammer et al 2011 , Boyd and Juhola 2015 , Creutzig et al 2016 ). Global energy optimization models show that advanced technologies, behavioural changes and shared socioeconomic pathways, enable rapid and deep decarbonisation to limit global warming to below 2 °C whilst at the same time reducing reliance on negative emissions technologies (NETs) by up to ∼18% compared standard set of technologies (Riahi et al 2017 , Napp et al 2019 ). Grubler et al ( 2018 ) find that low-energy demand scenarios can further obliviate NETs within the 1.5 °C target. Our research demonstrates that multi-pronged policy solutions like incentives, subsidies, voluntary and behavioural measures, conscious choice of selecting low-energy consumption solutions and greener lifestyles like purchasing e-vehicles, travelling by public transport, garden composting, EE measures at home and office can play a pivotal role at urban scale supporting the realization of such scenarios. Cities can thus make socio-technical transitions required for climate stabilization.

Acknowledgments

The views presented by authors are independent without any influence or conflict of interest. The first author acknowledges the Alexander von Humboldt Foundation for the research fellowship. The internal review platform- APSIS scoping software is provisioned by Mercator Research Institute on Global Commons and Climate Change, Germany. Thanks is due to Max Callaghan for orientation to and troubleshooting in APSIS operations. Chord diagrams are prepared using open access tool on https://sites.google.com/site/e90e50fx/home/talent-traffic-chart-with-chord-diagram-in-excel .

Data availability statement

All data that support the findings of this study are included within the article (and any supplementary information files).

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Climate Case Studies

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Seven case studies in carbon and climate

Every part of the mosaic of Earth's surface — ocean and land, Arctic and tropics, forest and grassland — absorbs and releases carbon in a different way. Wild-card events such as massive wildfires and drought complicate the global picture even more. To better predict future climate, we need to understand how Earth's ecosystems will change as the climate warms and how extreme events will shape and interact with the future environment. Here are seven pressing concerns.

The Far North is warming twice as fast as the rest of Earth, on average. With a 5-year Arctic airborne observing campaign just wrapping up and a 10-year campaign just starting that will integrate airborne, satellite and surface measurements, NASA is using unprecedented resources to discover how the drastic changes in Arctic carbon are likely to influence our climatic future.

Wildfires have become common in the North. Because firefighting is so difficult in remote areas, many of these fires burn unchecked for months, throwing huge plumes of carbon into the atmosphere. A recent report found a nearly 10-fold increase in the number of large fires in the Arctic region over the last 50 years, and the total area burned by fires is increasing annually.

Organic carbon from plant and animal remains is preserved for millennia in frozen Arctic soil, too cold to decompose. Arctic soils known as permafrost contain more carbon than there is in Earth's atmosphere today. As the frozen landscape continues to thaw, the likelihood increases that not only fires but decomposition will create Arctic atmospheric emissions rivaling those of fossil fuels. The chemical form these emissions take — carbon dioxide or methane — will make a big difference in how much greenhouse warming they create.

Initial results from NASA's Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) airborne campaign have allayed concerns that large bursts of methane, a more potent greenhouse gas, are already being released from thawing Arctic soils. CARVE principal investigator Charles Miller of NASA's Jet Propulsion Laboratory (JPL), Pasadena, California, is looking forward to NASA's ABoVE field campaign (Arctic Boreal Vulnerability Experiment) to gain more insight. "CARVE just scratched the surface, compared to what ABoVE will do," Miller said.

Methane is the Billy the Kid of carbon-containing greenhouse gases: it does a lot of damage in a short life. There's much less of it in Earth's atmosphere than there is carbon dioxide, but molecule for molecule, it causes far more greenhouse warming than CO 2 does over its average 10-year life span in the atmosphere.

Methane is produced by bacteria that decompose organic material in damp places with little or no oxygen, such as freshwater marshes and the stomachs of cows. Currently, over half of atmospheric methane comes from human-related sources, such as livestock, rice farming, landfills and leaks of natural gas. Natural sources include termites and wetlands. Because of increasing human sources, the atmospheric concentration of methane has doubled in the last 200 years to a level not seen on our planet for 650,000 years.

Locating and measuring human emissions of methane are significant challenges. NASA's Carbon Monitoring System is funding several projects testing new technologies and techniques to improve our ability to monitor the colorless gas and help decision makers pinpoint sources of emissions. One project, led by Daniel Jacob of Harvard University, used satellite observations of methane to infer emissions over North America. The research found that human methane emissions in eastern Texas were 50 to 100 percent higher than previous estimates. "This study shows the potential of satellite observations to assess how methane emissions are changing," said Kevin Bowman, a JPL research scientist who was a coauthor of the study.

Tropical forests

Tropical forests are carbon storage heavyweights. The Amazon in South America alone absorbs a quarter of all carbon dioxide that ends up on land. Forests in Asia and Africa also do their part in "breathing in" as much carbon dioxide as possible and using it to grow.

However, there is evidence that tropical forests may be reaching some kind of limit to growth. While growth rates in temperate and boreal forests continue to increase, trees in the Amazon have been growing more slowly in recent years. They've also been dying sooner. That's partly because the forest was stressed by two severe droughts in 2005 and 2010 — so severe that the Amazon emitted more carbon overall than it absorbed during those years, due to increased fires and reduced growth. Those unprecedented droughts may have been only a foretaste of what is ahead, because models predict that droughts will increase in frequency and severity in the future.

In the past 40-50 years, the greatest threat to tropical rainforests has been not climate but humans, and here the news from the Amazon is better. Brazil has reduced Amazon deforestation in its territory by 60 to 70 percent since 2004, despite troubling increases in the last three years. According to Doug Morton, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, further reductions may not make a marked difference in the global carbon budget. "No one wants to abandon efforts to preserve and protect the tropical forests," he said. "But doing that with the expectation that [it] is a meaningful way to address global greenhouse gas emissions has become less defensible."

In the last few years, Brazil's progress has left Indonesia the distinction of being the nation with the highest deforestation rate and also with the largest overall area of forest cleared in the world. Although Indonesia's forests are only a quarter to a fifth the extent of the Amazon, fires there emit massive amounts of carbon, because about half of the Indonesian forests grow on carbon-rich peat. A recent study estimated that this fall, daily greenhouse gas emissions from recent Indonesian fires regularly surpassed daily emissions from the entire United States.

Wildfires are natural and necessary for some forest ecosystems, keeping them healthy by fertilizing soil, clearing ground for young plants, and allowing species to germinate and reproduce. Like the carbon cycle itself, fires are being pushed out of their normal roles by climate change. Shorter winters and higher temperatures during the other seasons lead to drier vegetation and soils. Globally, fire seasons are almost 20 percent longer today, on average, than they were 35 years ago.

Currently, wildfires are estimated to spew 2 to 4 billion tons of carbon into the atmosphere each year on average — about half as much as is emitted by fossil fuel burning. Large as that number is, it's just the beginning of the impact of fires on the carbon cycle. As a burned forest regrows, decades will pass before it reaches its former levels of carbon absorption. If the area is cleared for agriculture, the croplands will never absorb as much carbon as the forest did.

As atmospheric carbon dioxide continues to increase and global temperatures warm, climate models show the threat of wildfires increasing throughout this century. In Earth's more arid regions like the U.S. West, rising temperatures will continue to dry out vegetation so fires start and burn more easily. In Arctic and boreal ecosystems, intense wildfires are burning not just the trees, but also the carbon-rich soil itself, accelerating the thaw of permafrost, and dumping even more carbon dioxide and methane into the atmosphere.

North American forests

With decades of Landsat satellite imagery at their fingertips, researchers can track changes to North American forests since the mid-1980s. A warming climate is making its presence known.

Through the North American Forest Dynamics project, and a dataset based on Landsat imagery released this earlier this month, researchers can track where tree cover is disappearing through logging, wildfires, windstorms, insect outbreaks, drought, mountaintop mining, and people clearing land for development and agriculture. Equally, they can see where forests are growing back over past logging projects, abandoned croplands and other previously disturbed areas.

"One takeaway from the project is how active U.S. forests are, and how young American forests are," said Jeff Masek of Goddard, one of the project’s principal investigators along with researchers from the University of Maryland and the U.S. Forest Service. In the Southeast, fast-growing tree farms illustrate a human influence on the forest life cycle. In the West, however, much of the forest disturbance is directly or indirectly tied to climate. Wildfires stretched across more acres in Alaska this year than they have in any other year in the satellite record. Insects and drought have turned green forests brown in the Rocky Mountains. In the Southwest, pinyon-juniper forests have died back due to drought.

Scientists are studying North American forests and the carbon they store with other remote sensing instruments. With radars and lidars, which measure height of vegetation from satellite or airborne platforms, they can calculate how much biomass — the total amount of plant material, like trunks, stems and leaves — these forests contain. Then, models looking at how fast forests are growing or shrinking can calculate carbon uptake and release into the atmosphere. An instrument planned to fly on the International Space Station (ISS), called the Global Ecosystem Dynamics Investigation (GEDI) lidar, will measure tree height from orbit, and a second ISS mission called the Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) will monitor how forests are using water, an indicator of their carbon uptake during growth. Two other upcoming radar satellite missions (the NASA-ISRO SAR radar, or NISAR, and the European Space Agency’s BIOMASS radar) will provide even more complementary, comprehensive information on vegetation.

Ocean carbon absorption

When carbon-dioxide-rich air meets seawater containing less carbon dioxide, the greenhouse gas diffuses from the atmosphere into the ocean as irresistibly as a ball rolls downhill. Today, about a quarter of human-produced carbon dioxide emissions get absorbed into the ocean. Once the carbon is in the water, it can stay there for hundreds of years.

Warm, CO 2 -rich surface water flows in ocean currents to colder parts of the globe, releasing its heat along the way. In the polar regions, the now-cool water sinks several miles deep, carrying its carbon burden to the depths. Eventually, that same water wells up far away and returns carbon to the surface; but the entire trip is thought to take about a thousand years. In other words, water upwelling today dates from the Middle Ages – long before fossil fuel emissions.

That's good for the atmosphere, but the ocean pays a heavy price for absorbing so much carbon: acidification. Carbon dioxide reacts chemically with seawater to make the water more acidic. This fundamental change threatens many marine creatures. The chain of chemical reactions ends up reducing the amount of a particular form of carbon — the carbonate ion — that these organisms need to make shells and skeletons. Dubbed the “other carbon dioxide problem,” ocean acidification has potential impacts on millions of people who depend on the ocean for food and resources.

Phytoplankton

Microscopic, aquatic plants called phytoplankton are another way that ocean ecosystems absorb carbon dioxide emissions. Phytoplankton float with currents, consuming carbon dioxide as they grow. They are at the base of the ocean's food chain, eaten by tiny animals called zooplankton that are then consumed by larger species. When phytoplankton and zooplankton die, they may sink to the ocean floor, taking the carbon stored in their bodies with them.

Satellite instruments like the Moderate resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua let us observe ocean color, which researchers can use to estimate abundance — more green equals more phytoplankton. But not all phytoplankton are equal. Some bigger species, like diatoms, need more nutrients in the surface waters. The bigger species also are generally heavier so more readily sink to the ocean floor.

As ocean currents change, however, the layers of surface water that have the right mix of sunlight, temperature and nutrients for phytoplankton to thrive are changing as well. “In the Northern Hemisphere, there’s a declining trend in phytoplankton,” said Cecile Rousseaux, an oceanographer with the Global Modeling and Assimilation Office at Goddard. She used models to determine that the decline at the highest latitudes was due to a decrease in abundance of diatoms. One future mission, the Pre-Aerosol, Clouds, and ocean Ecosystem (PACE) satellite, will use instruments designed to see shades of color in the ocean — and through that, allow scientists to better quantify different phytoplankton species.

In the Arctic, however, phytoplankton may be increasing due to climate change. The NASA-sponsored Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment (ICESCAPE) expedition on a U.S. Coast Guard icebreaker in 2010 and 2011 found unprecedented phytoplankton blooms under about three feet (a meter) of sea ice off Alaska. Scientists think this unusually thin ice allows sunlight to filter down to the water, catalyzing plant blooms where they had never been observed before.

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This report is part of a series of six case studies that explore lessons that are being learned by climate collaboratives from around the United States that are bringing together local governments and other stakeholders at the regional level to both reduce carbon pollution (mitigation) and prepare for the impacts of climate change (adaptation). Each case study explores the history and development structure and decision-making methods, funding sources, roles, and initiatives of each of these climate collaboratives. A synthesis report also explores lessons that can be learned by comparing the efforts of each collaborative on climate policy in their regions. These case studies were supported by a grant from the Kresge Foundation. In developing these case studies, the Georgetown Climate Center collaborated with the Alliance of Regional Collaboratives for Climate Adaptation (ARCCA).

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5 Steps to Creating a Climate Mitigation Strategy

• 04 Jun 2024

In October 2021, the United Nations (U.N.) held a global climate change conference (COP26) where over 5,200 businesses pledged to meet net-zero carbon targets by 2050. Yet, only 18 percent of CEOs reported having the clarity to operate their firms in line with the 1.5 degree Celsius warming trajectory.

As a business leader, it can be difficult to know where to start and how to make an impact on such a far-reaching, pressing issue.

“It may be easy for managers to fall into the trap of thinking that one business’s impact isn’t big enough to be worth doing,” says Harvard Business School Professor Forest Reinhardt, who teaches the online course Business and Climate Change alongside HBS Professor Michael Toffel, “or taking the perspective that it’s someone else’s responsibility to act—the government should take care of it, or consumers need to drive demand. But the lesson all business leaders can take from this course is that every firm can have an impact.”

To help you get started, here’s a primer on climate change and five steps to creating an actionable climate change mitigation strategy.

Related: Listen to Professor Reinhardt discuss climate change and the tragedy of the commons on The Parlor Room podcast , or watch the episode on YouTube .

What Is Climate Change?

Climate change refers to long-term shifts in temperature and weather patterns. Although some changes in Earth’s climate are natural, most are anthropogenic —or caused by humans.

Human activity has disrupted Earth’s natural regulatory systems—namely, the greenhouse effect, carbon cycle, and water cycle—by emitting more greenhouse gas into the atmosphere than can be naturally absorbed.

The four naturally occurring greenhouse gases are:

• Carbon dioxide (CO 2 )
• Methane (CH 4 )
• Nitrous oxide (N 2 O)
• Water vapor (H 2 O) 2

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Ways in which humans—and businesses in particular—generate excess greenhouse gases include:

• Burning fossil fuels to generate electricity
• Producing cement, steel, and iron for construction
• Waste management, such as landfills and trash incinerators
• Transportation, including cars, trucks, planes, trains, and ships
• Clearing land for agriculture
• Raising livestock
• Industrial processes like refrigeration and air conditioning

Because of these processes, businesses have a major impact on climate change and its effects, including higher average global temperatures and extreme weather events like storms, heat waves, temperature fluctuations, and rising sea levels, which cause flooding.

“Climate change is one of the world’s biggest societal challenges,” Reinhardt says in Business and Climate Change . “Companies will have to play an active role if we, as a society, are to have any realistic hope of managing the challenges presented by climate change.”

Related: How Climate Change Affects Business Strategy

5 Steps to Developing a Climate Change Mitigation Strategy

1. identify motivations.

The first step to creating a climate change mitigation strategy is addressing your motivations.

“Some firms mitigate in anticipation of potential regulations, such as energy efficiency standards, carbon pricing systems, or technology mandates and bans,” Toffel says in Business and Climate Change . “Preparing for pending regulatory requirements like this can ease a company’s transition to future regulation.”

Getting ahead of regulatory requirements can qualify your company to weigh in on the regulatory planning process and help reduce your risk of a difficult transition with enforced requirements.

Other motivations for climate mitigation include:

• Aligning with your company’s values and contributing to its culture
• Supporting recruiting and retention efforts to attract sustainably minded employees
• Bolstering brand voice
• Encouraging engagement from customers who care about environmentally ethical consumption
• Labeling your brand as an industry leader

Listing your motivations before diving into the planning process can provide a guiding purpose throughout your efforts.

Related: Making the Business Case for Sustainability

2. Measure a Baseline Carbon Footprint

Carbon footprint is a term used to describe the total amount of greenhouse gas emissions—typically measured in metric tons—associated with an individual, a company, or a product. It can either measure carbon dioxide emissions or carbon dioxide equivalent , which aggregates all greenhouse gas emissions into one metric.

Identify Emissions Sources

To measure your organization’s baseline carbon footprint, start by identifying its emissions sources. In Business and Climate Change , Toffel explains the categorization method the Greenhouse Gas Protocol—a standardized global framework—presents:

• Scope 1: Emissions produced onsite by sources your company owns or controls
• Scope 2: Emissions generated offsite to create electricity, steam, and heating and cooling energy
• Scope 3 Upstream emissions are those associated with a product’s supply chain
• Scope 3 Downstream emissions result from post-manufacturing activities, including distribution, use, and disposal

Conduct a Life Cycle Assessment

If calculating a specific product’s carbon footprint, you can conduct a Life Cycle Assessment to visualize emissions sources at each of its five life stages:

• Sourcing: Where do the raw materials come from?
• Manufacturing: What processes do you use to make the product?
• Distribution: How do you disseminate the product to retailers and end users?
• Use: What’s involved in the processes of using the product?
• End-of-life: What happens to the product when you’re done using it?

Gather Data and Calculate Your Carbon Footprint

Next, gather emissions data.

“While identifying emissions sources and establishing the boundaries of measurement is important, it’s just the start of assessing a carbon footprint,” Toffel says in Business and Climate Change.

Inventory how much greenhouse gas each emissions source discharged over a set timeframe. Next, convert each into its carbon dioxide equivalent using its emissions factor , a numeric estimate of the quantity of greenhouse gas emissions a process or an activity produced.

Multiply the emissions amount by the emissions factor to calculate the carbon dioxide equivalent for the period. Finally, add up the carbon dioxide equivalents for each emissions source to determine your company’s carbon footprint.

3. Analyze Mitigation Options

After calculating your organization’s carbon footprint, identify and analyze your mitigation options.

Brainstorm how to replace the identified emissions sources with lower- or no-emission alternatives. Welcome innovative ideas , as climate mitigation is still a relatively young field. You can also hire a sustainability consultant for guidance on feasible options.

Once you have a list of mitigation options, analyze them using a marginal abatement cost curve.

“A marginal abatement cost curve enables managers to compare projects in terms of cost-effectiveness and effect on emissions reduction,” Reinhardt says in Business in Climate Change.

Using the tool, prioritize projects based on which will have the biggest impact on emissions reduction and be most cost-effective. It’s not always the case that the most expensive options provide the largest emissions reduction. Keep in mind that some climate change mitigation activities are government-subsidized, making them less costly to pursue.

4. Set Emissions Reduction Targets

Once you’ve decided which mitigation project to pursue, set clear goals . How will you determine success and measure progress?

According to Business and Climate Change , three popular types of mitigation targets are:

• Percentage reduction targets: Set a goal to reduce greenhouse gas emissions by some percentage by a target year relative to a baseline year
• Net zero targets: Commit to reducing greenhouse gas emissions to as close to zero as possible and then completely offset any remaining emissions by purchasing carbon credits
• Science-based targets: Set science-based targets per the Science Based Targets Initiative (SBTi) that align with the Paris Agreement’s goal to limit temperature rise to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels

No matter your target, setting it requires four elements:

• Activity scope: What projects and activities does it include?
• Baseline year: What timeframe will you compare the target carbon footprint against?
• Target year: What date will you achieve it by? Do you have shorter-term milestones?
• Target value and type: What’s the numeric metric you aim to achieve? For example, “reduce carbon dioxide equivalent by 50 percent” or “reduce carbon dioxide equivalent by 10 metric tons per square meter of land.”

5. Implement Mitigation Activities

Finally, implement your prioritized mitigation activities. Track progress toward your target and ensure you hit the necessary milestones along the way.

If your original strategy doesn’t yield your anticipated results, don’t be afraid to reevaluate and pivot.

“The mitigation planning process isn’t really linear,” Toffel says in Business and Climate Change. “Instead, it can be viewed as a continuous improvement process with iterations of measuring, analyzing, implementing, and evaluating mitigation activities.”

Gain the Knowledge to Enact Change

As you approach your climate change mitigation journey, remember that there’s always more to learn. By enrolling in a course like Business and Climate Change , you can gain the scientific foundation—as well as the tools and nuances—to inform your strategy for navigating this global challenge.

You can also learn directly from business leaders who’ve faced climate change firsthand and use their experiences to shape your organization’s mitigation efforts.

With the right motivations, targets, and baseline, you can help mitigate climate change’s effects.

Do you want to learn more about adapting to and mitigating climate change? Explore Business and Climate Change —one of our online business in society courses —and download our free e-book on how to become a purpose-driven, global business professional.

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Blog Just transitions and the importance of social protection reforms for ambitious climate action

As it is crucial to consider the effects of climate change mitigation policies on various population groups, we explore two policy options —carbon pricing and removal of fossil fuel subsidies. In our latest microsimulation study , we model the impacts of these climate policies on poverty rates and inequality levels. Our study—conducted jointly by SASPRI, LSE, IDOS, and GIZ—also analyse which social protection reform options are most effective at offsetting the negative impacts for those likely to face downsides in low- and middle-income countries. 

What impact do climate change mitigation policies have on poverty and inequality?

Carbon pricing and the removal of fuel subsidies may negatively affect some people and vulnerable groups disproportionately. The main focus of our analysis is on carbon pricing in Ecuador, Indonesia, South Africa, Tanzania, Viet Nam, and Zambia. Carbon pricing is a globally considered mitigation measure with significant direct impacts on the financial situation of households. We also consider the removal of fuel subsidies in Indonesia, South Africa, and Zambia.

Key findings  

In Ecuador, South Africa, and Viet Nam, model simulations indicate that an introduction of carbon pricing disproportionately disadvantages people in the lower income/consumption quintiles. Compared to even a low carbon tax rate, the removal of fossil fuel subsidies leads to smaller relative changes in household purchasing power (measured as mean consumption), but also affects the poorest quintile the most in both Indonesia and South Africa. In Zambia, better off households feel more of the effects of fuel subsidy removal. This illustrate why social protection will be important to help mitigate againstthe regressive nature of climate policies, as illustrated in Figure 1. 

Source: Gasior et al. (2024: 30). 

Additional revenues from carbon pricing and subsidy removal can be used to expand social protection

Using the SOUTHMOD tax-benefit microsimulation models for Ecuador, Viet Nam, Tanzania, and Zambia,  SAMOD for South Africa, and  INDOMOD for Indonesia, we assess what would happen if revenue generated by climate policies is used to expand the existing social protection system to target vulnerable populations. We simulate three reform options: 

All three reform scenarios cushion the overall drop in mean income/consumption. While they lead to significant income/consumption increases at the bottom of the distribution across countries and reform scenarios, the same effects are not observed towards the top of the distribution. 

In four of the six countries (Ecuador, Indonesia, South Africa, and Viet Nam), the modelled social protection reforms not only cushion the shock of carbon pricing, but result in an overall reduction in the poverty headcount. In Tanzania and Zambia, the poverty headcount is not significantly reduced, because the revenue generated is too small to fill the gaps in the current social protection system.  

The generosity reform scenario

An increase in benefit amounts leads to a more significant reduction in poverty than an expansion of coverage in Ecuador, Indonesia, Viet Nam, and South Africa.  

When poverty is concentrated at the bottom of the distribution, the generosity scenario results in better cushioning effects for those in poverty than the other reforms considered. This is particularly notable in the case of Viet Nam.

However, increasing generosity for those currently covered by social assistance does not necessarily provide the best cushioning effects for those in the lower quintiles because the scale of the impact depends on how well the current social protection system covers those in need. 

The coverage reform scenario

Extending social protection coverage to more people can lead to better results for lower-income population groups, i.e., the lower quintiles in the income distribution.

In Zambia in particular, increasing coverage generates a higher relative increase in average incomes for people in the bottom quintile, by reducing coverage gaps in the current social protection system.

The categorical reform scenario

The introduction of a categorical benefit for vulnerable groups has a stabilising effect on income/consumption in most of the countries considered. This comes at the cost of smaller increases in average income/consumption for people in the lower quintiles, compared to the other two reform scenarios (except in South Africa and Ecuador).  

Categorical benefits for specific groups are an option for countries where poverty is not solely concentrated at the very bottom of the income/consumption distribution but affects a large proportion of the population, such as Tanzania and Zambia, with potentially easier administration.

Our study highlights that the reform impact notably depends on the following, e.g.:

Fiscal space may also be needed to strengthen the functionality of the social protection system, by investing in infrastructure (data and information, delivery mechanisms, physical and staff capacities, etc.).  

What are the policy recommendations emerging from the study?

Social protection is a key policy area to complement climate change mitigation and achieve a just transition. Effective social protection systems can enable more ambitious climate action and sustain public support for it. Research shows that climate change mitigation policies are more likely to be supported if the revenue is used to support and protect populations groups (likely to be) affected (Dabla-Norris et al., 2023). Policymakers should understand how the existing social protection system works and what its limitations are to better guide social protection reform(s). Reforms need to consider the current poverty situation, fiscal space, the size of the national carbon footprint, and the current capacity of the existing social protection system.

Social protection policies need to be planned well in advance as part of a just transition package. In this way, social protection can alleviate, or even avoid, the negative socio-economic effects of climate change mitigation policies on, especially, vulnerable people and those already living in poverty. Options at the global level, e.g., a global carbon tax, are likely to have a much stronger impact on poverty reduction than national-level carbon pricing in the Global South.

Learn more about which social protection reforms may be most suitable for your country contexts in the full study .

Christina Dankmeyer is Advisor Just Transition and Social Protection Financing at Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH.

Katrin Gasior is Senior Research Fellow at Southern African Social Policy Research Insights (SASPRI).

Gemma Wright is co-Executive Director of Southern African Social Policy Research Insights (SASPRI).

The views expressed in this piece are those of the authors, and do not necessarily reflect the views of the Institute or the United Nations University, nor the programme/project donors.

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Climate change mitigation and productivity gains in livestock supply chains: insights from regional case studies

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• Published: 21 May 2016
• Volume 17 , pages 129–141, ( 2017 )

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• Anne Mottet 1 ,
• Benjamin Henderson 2 ,
• Carolyn Opio 1 ,
• Alessandra Falcucci 1 ,
• Giuseppe Tempio 1 ,
• Silvia Silvestri 3 ,
• Sabrina Chesterman 4 &
• Pierre J. Gerber 1 , 5  

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Livestock can contribute to climate change mitigation by reducing their greenhouse gas emissions and by increasing soil carbon sequestration. Packages of mitigation techniques can bring large environmental benefits as illustrated in six case studies modeled in the Global Livestock Environmental Assessment Model developed by FAO. With feasible technical interventions in livestock production systems, the mitigation potential of each of the selected species, systems and regions ranges from 14 to 41 %. While comparably high mitigation potentials were estimated for ruminant and pig production systems in Asia, Latin America and Africa, large emission reductions can also be attained in dairy systems with already high levels of productivity, in OECD countries. Mitigation interventions can lead to a concomitant reduction in emissions and increase in production, contributing to food security. This is particularly the case for improved feeding practices and better health and herd management practices. Livestock systems also have a significant potential for sequestrating carbon in pasturelands and rangelands through improved management, as illustrated in two of the six case studies in this paper.

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Acknowledgments

This research was supported by the AnimalChange Project (FP7/2007-2013, Grant Agreement No. 266018), the Mitigation of Climate Change in Agriculture project (MICCA) and the CGIAR research program on Climate Change Agriculture and Food Security (CCAFS) and benefited from valuable comments from Henning Steinfeld, Tim Robinson, Jeroen Dijkman, Caroline Chaumont, Harinder Makkar and two anonymous reviewers.

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Mottet, A., Henderson, B., Opio, C. et al. Climate change mitigation and productivity gains in livestock supply chains: insights from regional case studies. Reg Environ Change 17 , 129–141 (2017). https://doi.org/10.1007/s10113-016-0986-3

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The 60th session of the Bonn Climate Change Conference , hosted by the United Nations Climate Change Conference, will take place from 3 to 13 June 2024 at the World Convention Center in Bonn, Germany.

This conference is a pre-sessional event in preparation for the COP29 . Attended by an estimated 3,000 to 4,000 delegates representing nations worldwide, these biennial gatherings serve as a pivotal platform for advancing climate action. The discussions, spanning a diverse range of topics, play a crucial role in setting the stage for collaborative efforts and consensus-building towards effective climate policy and implementation strategies.

On the first day of the Conference a side-event with focus on Nationally Determined Contributions (NDCs) and National Adaptation Plans (NAPs), will convene Parties in a round table discussion serving to demonstrate how countries are taking stock of water action for climate mitigation and adaptation measures, and to shed light on strategic points for mainstreaming water as a necessary aspect for NDC and NAP implementation.

Bonn Climate Change Conference side-event: Building water-wise NDCs and NAPs

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During the side-event a new study carried out by the International Universities for Climate Alliance (IUCA) at the request of the UN-Water Expert Group on Water and Climate Change will be presented. The study titled ' Water for Climate Mitigation: Estimating the Global Freshwater Requirements of Climate Mitigation Measures ' offers preliminary global estimates of water requirements associated with the climate mitigation measures required to reduce greenhouse gas emissions and sequester carbon in the atmosphere.

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India: A Case Study in Climate Mitigation and Adaptation

This article explores the difficult trade-offs that need to be made between the competing claims of climate mitigation, adaptation, and economic development..

Thursday, September 14, 2023

By Maxine Nelson

This article has been extensively updated, incorporating new COP 27 commitments, Reserve Bank of India (RBI) statements and current green bond issuance. It was originally published Oct. 18, 2021.

After decades of population growth and economic development, India is now the third largest emitter of greenhouse gases in the world. In addition, India is among the countries most vulnerable to climate change due to its geography and dependence on agriculture.

It has been estimated that if emissions are not significantly reduced, India could suffer economic losses of USD 35 trillion . Indeed, much of India has been experiencing annual heatwaves followed by intense flooding, and in 2021 alone it experienced even more  extreme weather events — including cyclones and a glacier collapse. Thus, India makes a thought-provoking case study for policymakers and risk professionals given the difficult trade-offs that need to be made between the competing claims of climate mitigation, adaptation and economic development.

Climate Change’s Effect on India

The banking regulator, Reserve Bank of India (RBI) , explains that “India has witnessed changes in climatic patterns in line with the rest of the world… the rainfall pattern, particularly with respect to the [south west monsoon] SWM, which provides around 75 percent of the annual rainfall, has undergone significant changes. Moreover, the occurrence of extreme weather events like floods/unseasonal rainfall, heat waves and cyclones has increased during the past two decades, and data reveal that some of the key agricultural states in India have been the most affected by such events.”

A more recent, detailed RBI study points out that “it is the increased frequency of extreme weather occurrences that is breaking the back of our capability to cope with natural disasters.” As shown by India’s nationally determined contributions (NDCs) — the actions it has committed to take to reduce its emissions and adapt to the impacts of climate change — it is among the most vulnerable countries in the world to the impact of accelerated sea level rise from global warming. This is due to its long coastline, large number of islands and population of 170 million living in coastal regions.

The RBI also notes that precipitation and temperature — the two key climate indicators — “play a crucial role in the overall health of the Indian economy.” As well as affecting food production, the extreme weather in agricultural states impacts employment and GDP, with approximately 44% of the working population employed in agriculture and allied sectors which contribute about 20% of GDP, according to M.K. Jain, the deputy governor of the Reserve Bank . Several challenges confronting Indian agriculture, including diminishing and degrading natural resources and unprecedented climate change, need to be tackled for the long-term sustainability and viability of Indian agriculture.

However, there is uncertainty over how large the impacts might be. The Swiss Re Institute , for example, estimates a 35% reduction in the level of India’s GDP by 2050 if greenhouse gas emissions are not reduced globally, and approximately a 6% GDP reduction even if the Paris Agreement goals are met. An Oxford Economics report “Estimating the Economic Impact of Global Warming” has framed the impact differently, estimating that India’s GDP could be 90% lower in 2100 than it would be if there was no climate change, suggesting that climate change has the potential to absorb all of India’s future prospective growth in income per capita. And  Deloitte  has estimated USD 35 trillion of economic losses by 2070. While these different approaches produce diverse estimates, they all show that the impact will be big and require additional investments in both mitigation and adaptation.

India’s Effect on Climate Change

Not only will the changing climate have a significant impact on India, but India is also expected to have a significant impact on the climate. Although historically it has not had high emissions, India rose to the number three spot in the national emissions rankings 15 years ago, behind China and the U.S. The RBI noted that “With the increase in population, the cumulative level of greenhouse gas (GHG) emissions has increased, resulting in a rise of average temperature. According to a study by the International Energy Agency (IEA), India emitted 2,299 million tonnes of carbon dioxide (CO 2 ) in 2018, a rise of 4.8% over the previous year.”

Unfortunately, India’s future potential emissions are not yet aligned with the Paris Agreement goals. India’s NDCs currently correspond to temperature increases above 3°C, according to Climate Action Tracker . (You can find out more about NDCs and their place in the Paris Agreement in this  short article . ) India increased its commitment to reduce greenhouse gas emissions at COP 26, the 2021 annual meeting of the signatories of the Paris Agreement, where it pledged to cut its emissions to net zero by 2070. While this was a large increase in commitment, it isn’t yet aligned with the worldwide goal of cutting emissions to net zero by 2050 needed to limit global warming to 1.5°C.

Maxine Nelson

In advance of COP 27, India has again increased its commitment and pledged to a 45% reduction in GDP emissions intensity by 2030 — marking an 10% increase from the previous pledge. Any emissions reduction is helpful to mitigate climate change. However, as the pledge is based on emissions intensity and not absolute emissions, emissions can continue increasing as the economy expands. This pledge, therefore, doesn’t meet the net-zero goal of reducing emissions by 45% by 2030. Still, the effort required to overcome the challenge of rapidly expanding an economy while decreasing emissions intensity needs to be appreciated.

To further mitigate climate change, India may need to agree to reduce its emissions even more — a big task for a developing economy with average annual energy consumption of a third the global average, and per capita emissions already 10 times lower than that of the U.S., four times lower than China, and three times lower than Europe. With IPCC reports highlighting the urgency of tackling climate change quickly to reduce the loss and damage for humans and ecosystems, it is even more important that emissions reductions are ambitious.

Financing Mitigation and Adaptation

A 2021 RBI Financial Stability Report noted that climate change and the associated mitigating policy commitments are “set to reshape the macroeconomic and financial landscape”. Extensive funding is needed both to reduce future emissions and to finance the adaptation needed to manage the impacts of climate change. In their 2016 NDC, India estimated that at least USD 2.5 trillion (at 2014-15 prices) would be required for meeting its climate change actions between 2016 and 2030. And the International Energy Agency estimates that nearly 60% of India’s CO 2 emissions in the late 2030s will be coming from infrastructure and machines that do not exist today. If this investment is to be sustainable, USD 1.4 trillion extra funding (above that required for current policies) is needed over the next 20 years.

Like most of the world, green bond issuance in India — which could provide some of this funding — is currently a small proportion of all bond issuance.  The rate of issuance is increasing, however, with USD 21.6 billion of green, sustainable or social bonds issued in 2022. And in 2023, the Government of India entered the green finance market issuing USD 2 billion of green bonds to finance their spending on a range of projects including solar power, green hydrogen and afforestation. As they obtained a greenium (lower financing costs than other equivalent bonds), we should expect to see more of these issued in the future.

There are also substantial opportunities in other financial markets, such as the  development of a derivatives market   to aid adaptation via products such as:

• agricultural commodity derivatives, which can help reduce risks by enabling continuous price discovery and providing hedging
• weather derivatives, which can hedge the risks of high-probability, low-risk events

Of course, meeting the needs of climate change financing carries the usual financial risk implications of any lending. An RBI analysis shows that banks’ direct exposure to fossil fuels (through electricity, chemicals and cars) is 10% of total outstanding non-retail bank credit, so it should have a limited impact on the banking system. However, it notes that many other industries indirectly use fossil fuels and their impacts also need to be closely monitored.

Regulatory Response

The RBI has noted that policy measures such as a deepening of the corporate bond market, standardization of green investment terminology, consistent corporate reporting and removing information asymmetry between investors and recipients can make a significant contribution in addressing some of the shortcomings of the green finance market.

Like in most of the rest of the world, there is an increasing regulatory focus on climate risk. The RBI Governor has stated that guidelines will be issued about disclosure of climate-related risks, and also scenario analysis and stress testing. This followed last year’s RBI consultation which asked for inputs on a comprehensive range of topics from climate risk governance to strategy, and risk monitoring, management and mitigation at regulated entities. This consultation, in turn, built on the results of an RBI survey of banks that was also published last year. The survey found that “although banks have begun taking steps in the area of climate risk and sustainable finance, there remains a need for concerted effort and further action in this regard.” It also found that board-level engagement is inadequate, and few banks had a strategy for incorporating climate risk into their risk management framework. To see what leading climate risk firms are doing globally look at GARP’s whitepaper: “ Climate Risk Leadership: Lessons From 4 Annual Surveys .”

Given the widespread impact of climate change, it isn’t just the banking regulator that is looking at how climate risk will affect firms in its jurisdiction. In 2021, the Securities and Exchange Board of India (SEBI) mandated that the largest 1,000 listed firms complete a Business Responsibility and Sustainability Report . The report asks for information like material ESG risks and opportunities and their financial implications; sustainability related targets and performance; and their greenhouse gas emissions. Companies’ value chains also need to be assessed. This requirement is being progressively rolled out from 2023 to 2027, with the largest companies also required to get assurance of their disclosures.

In addition, SEBI has altered the rules for mutual funds , allowing them to have multiple ESG schemes with different strategies; in the past, a mutual fund could only have one ESG fund. This increase in scope follows one for green debt securities , which was expanded to include bonds such as blue bonds (sustainable water management and marine sector), yellow bonds (solar energy generation and transmission), transition bonds and adaptation bonds. Both of these expansions in scope should increase financing for sustainability related initiatives.

Reflecting the fact that addressing climate change is a global problem, needing both local and global solutions, the RBI joined the Network for Greening the Financial System (NGFS) in April 2021. The NGFS’s purpose is to strengthen the global response required to meet the goals of the Paris Agreement and to enhance the role of the financial system to manage risks and to mobilize capital for green and low-carbon investments. These goals align very well with the work India needs to undertake to make not just its financial system resilient to the risks from climate change, but to balance mitigation, adaptation, and economic development across the country.

Maxine Nelson , Ph.D, Senior Vice President, GARP Risk Institute, currently focusses on sustainability and climate risk management. She has extensive experience in risk, capital and regulation gained from a wide variety of roles across firms including Head of Wholesale Credit Analytics at HSBC. She also worked at the U.K. Financial Services Authority, where she was responsible for counterparty credit risk during the last financial crisis.

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• Published: 19 March 2024

Effective climate action must integrate climate adaptation and mitigation

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This work was supported by the UK Economic and Social Research Council through the Place-Based Climate Action Network (P-CAN) (ref. ES/S008381/1).

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Comprehensive analysis of the impacts of climate and land use changes on flood damage (Case study: AqQala, Iran)

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Arash Majidi , Seyed Abbas Hosseini , Sara Nazif , Bagher Ghermezcheshmeh; Comprehensive analysis of the impacts of climate and land use changes on flood damage (Case study: AqQala, Iran). Journal of Water and Climate Change 2024; jwc2024094. doi: https://doi.org/10.2166/wcc.2024.094

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Population growth, community development, and waste generation impact climate, land use, water resources, and urban heat island effect. This research assesses the impacts of climate and land use changes on flood damage for different return periods (RPs) in AqQala area, Iran. Climate change anticipation is conducted using the CMCC-ESM2 model under shared socioeconomic pathways (SSPs) 126, 370, and 585 of the Intergovernmental Panel on Climate Change (IPCC) sixth assessment report (Coupled Model Intercomparison Project Phase 6 – CMIP6). The LARS-WG model is used to downscale climatic information, and land use mapping is processed through Landsat satellite images in ENVI 5.3. The Markov chain method is implemented for 2050 and 2080 via TerrSet. Hydrographs and inundation maps are generated by an Autodesk Storm and Sanitary Analysis (SSA) and a Hydrologic Engineering Center's River Analysis System (HEC-RAS) models. Results show an increase in average annual precipitation (up to 46%) and temperatures (up to 3.39 °C) under different SSP scenarios until 2080. The result indicates that land use changes are more significant than climate change. Peak flood discharge and damages could escalate by 38 and 29%, respectively, in the worst-case scenario. Eco-friendly design and implementation are crucial for improving the situation.

The influences of climate and land use changes on flood damage on different return periods were assessed.

Climate change anticipation is implemented by applying the CMCC-ESM2 model of CMIP6.

It is found that the impact of land use change regarding flood damage is more fatal than climate change.

The necessity of dynamic adaptive policies to mitigate the future flood damage.

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ASU scientists use new technologies to monitor, mitigate heat exposure risk

Studies pave the way for further extreme heat risk mitigation actions, future studies.

ASU Associate Professor Ariane Middel pulls MaRTy, which she uses to conduct shade research, along a sidewalk on the Tempe campus. Photo by Deanna Dent/ASU

With central Arizona temperatures hitting triple digits again, heat research experts are working to better understand the effects of extreme heat on cities and their populations.

"Extreme heat poses a pressing global health concern, with urban areas particularly at risk due to the heat-island effect and the more recent hotter summers due to climate change," said Konrad Rykaczewski , associate professor of mechanical engineering in the Ira A. Fulton Schools of Engineering at Arizona State University. 

An ASU team, led by Rykaczewski, along with colleagues Jennifer Vanos and Ariane Middel, are currently working on a four-year, $2 million National Science Foundation project to better quantify the impact of heat on the human body.

Now, in some of their first results, they have pioneered  better measurements of the heat’s effect on the human body with a customized outdoor thermal manikin, called ANDI, coupled with a state-of-the-art mobile biometeorological station developed by Middel’s team, called MaRTy .

Read more about MaRTy and ANDI

•  Do trees provide the best shade for urban environments?

• Meet the world's first outdoor sweating, breathing and walking manikin

• Follow @ ASUMaRTy and @ ASUThermalANDI on X

The team used insights from this complex, one-of-a-kind instrumental suite to develop cost-effective, simple ways to measure heat radiation at outdoor locations with low-cost sensors (cylinders) to provide critical microclimate data in at-risk areas.

The studies, published in the journals International Journal of Biometeorology  and Science of the Total Environment , showcase innovative approaches to understanding and combating the growing challenges of extreme heat.

Together, these groundbreaking tools offer ways to capture heat fluxes on the human body more accurately during high-temperature events, significantly affecting human comfort and health.

T heir results add to prior computational work published in International Journal of Biometeorology , where the researchers showed that the cylindrical sensor shape can provide accurate prediction of radiation fluxes experienced by all body types within the adult population in the United States.

Innovative approaches to heat measurement

The summer heat in central Arizona is often compared to turning on an oven. Just like an oven, heat can be measured by factors such as air temperature, humidity, thermal radiation and heat circulation or convection.

“Widely available weather forecasts and real-time reports do not provide information on local microclimate s that can change across small distances within a city,” said Ariane Middel , an ASU associate professor in the School of Arts, Media and Engineering and the School for Computing and Augmented Intelligence.

"Also, air temperature or simple heat indices, such as the heat index or humidex, do not quantify the heat load on the human body. In particular, turbulent wind flow and solar radiation hitting a sun-exposed person significantly impact heat stress but are not accounted for,” she said.

Middel adds that outdoor heat exposure has never been measured with realistic human body shapes in extremely hot outdoor conditions. This data gap leads to unvalidated assumptions underlying radiation sensors and disagreement in often-used theoretical convection models.

Thermal manikin mimics human exposure

A state-of-the-art thermal manikin, called ANDI, was equipped with sensors across 35 body zones, and deployed in various urban outdoor settings. This was the very first time a thermal manikin has been used in outdoor settings.

“We leveraged a one-of-a-kind thermal manikin alongside high-end wind sensors and the MaRTy cart to verify our measurements,” lead researcher Rykaczewski said.

MaRTy is a sophisticated mobile technology that can make “gold standard” measurements to verify the air temperature, humidity, wind speed and six-directional shortwave and longwave radiation that ANDI would experience.

Like legacy manikins, ANDI’s shell contains temperature sensors and can be resistively heated. But in addition, ANDI’s shell has heat flux sensors that can be water-cooled with built-in liquid channels thereby enabling convective and direct radiative flux measurements in hot conditions unattainable with prior instrumentation.”

The manikin, MaRTy and anemometers were used during the 2023 summer heat wave in the Valley and deployed for over 20 days in Tempe, under extremely hot conditions (air temperatures up to 47 C, or 117 F, and high sunlight).

They measured radiation and convection heat exchange at ANDI’s skin surface at three different locations chosen to provide unobstructed solar radiation as well as two types of shade (industrial, under a building and natural shade, provided by native Palo Verde trees).

“Usually, thermal manikins are operated in pristine climatic chambers while their support systems are in adjacent labs,” Rykaczewski said. “In contrast, the entire ANDI system — including power and control electronics and water chiller (totaling over 1,000 pounds) — is mobile and ruggedized to operate in extreme heat and dust.”

What did they find? First, their approach showed human bodies can be modeled as cylinders for more accurate heat exposure assessments, even in highly turbulent conditions and under intense solar radiation.

“Using ANDI convection measurements and new geometry-rooted analysis, we demonstrated that different body parts are well-approximated by cylinders, even in turbulent flow that is difficult to generate in a wind tunnel,” Rykaczewski said.

“We were also able to determine that a cylinder with about a 7-inch diameter would be equivalent to a whole human body. With this equivalent diameter, we showed that we can use classical engineering correlations to accurately calculate the heating or cooling of the whole body by complex air flows, indoor and outdoor. This generally applicable approach resolves about 70 years’ worth of highly conflicting convection correlation in the literature.”

The research also showed that regardless of ANDI’s body orientation, MaRTy and ANDI radiation measurements agreed, even under high solar conditions. This agreement validated the main assumption underlying the data, that from radiation perspective, a human body can be treated as a cylinder.

Paving a path for affordable sensors

While radiation accounts for much of the human heat exposure, it is rarely used as a heat metric due to the lack of cost-effective and accurate sensors.

Knowing how specific towns, streets and housing communities are affected by heat can better help first responders mitigate threats to human health.

Based on the new insights from the ANDI radiation measurements, the ASU scientists could develop a simple device that can serve as a portable, street-level heat weather station.

Rykaczewski and his team wanted to demonstrate a simple and easy-to-fabricate three-cylinder shortwave and longwave radiometer that also measures the cylinders’ convection. Using off-the-shelf, cost-effective and readily available materials, they fabricated two combinations of three cylinders with varying surface properties.

This homemade heat weather station melds the concepts of a traditional globe-shaped radiometer with a cylindrical representation of the human body, offering a more realistic assessment of heat exposure than classical methods.

These cylinder-shaped devices were spray-painted black, white or left in a natural aluminum finish. To first test the device, the team went to the rooftop of their research home — the Walton Center for Planetary Health — to perform sunrise-to-sunset measurements. The measurements were paired with MaRTy , again serving as the gold reference standard.

From the rooftop tests, the research team found that their homemade devices could closely replicate the results from MaRTy and be a reasonable approximation.

Next, they extensively tested the devices at 14 outdoor sites, chosen to mimic pedestrian walking areas throughout the Phoenix metro area.

These were taken during the July 2023 record-setting heat wave in Tempe, where temperatures exceeded 110 degrees Fahrenheit for 30 straight days. Temperatures were measured from noon to 2:30 p.m., and stable in temperature from 109 to 113 degrees Fahrenheit (43 to 45 degrees Celsius).

The sites were chosen for their differences in exposure, which varied from fully sun-exposed areas over distinct surfaces (such as asphalt, concrete and grass) to partially exposed urban canyons and courtyards, and spaces covered by a variety of natural (native and non-native trees) and industrial shade (fabric sun sail, perforated metal sheet and movable solar panels).

“We demonstrated that shortwave and longwave radiation measured with the three cylinders closely match MaRTy’s,” Middel said. “This novel method is a promising, cost-effective and easy-to-fabricate approach to assess human heat exposure, including radiation and wind, without $25,000 equipment (the cost of MaRTy).”

Now, the ASU researchers are refining their radiation measurement approach and extending to measuring convection to deploy again for the summer of 2024.

“The novel setup could be used in affordable weather stations and deployed across urban landscapes to build human-relevant heat sensing networks,” Middel said.

Future directions

The insights gained from these studies can further empower city planners, policymakers and emergency response teams with the data needed to enhance heat action plans and effectively reduce heat-related health risks.

"By leveraging hyperlocal biometeorological data, we can significantly improve emergency responses and heat mitigation strategies," said Jennifer Vanos , a co-researcher in the study and associate professor in the School of Sustainability at ASU.

These tools' affordability and ease of deployment make them ideal for widespread use. They promise to transform how cities understand and respond to the challenges of extreme heat. 

Looking ahead, the research teams at ASU plan to expand their studies to include dynamic, real-world scenarios, such as the impact of clothing and different postures on heat exposure.

“Thus far, we only conducted measurements with the manikin in a static standing position, emphasizing front wind exposure,” Rykaczewski said. “Both the radiative and the convective heat exposure can be impacted by changes in posture (e.g., sitting vs. standing), the subject’s motion and the presence of clothing.”  

Next, the ASU team wants to build on the recently introduced suite of instruments to measure the dynamics of physiological responses — like core and skin temperatures or sweat rate — to specific combinations of hot microclimates (quantified using MaRTy and anemometers) with human factors such as metabolic rates (adjusted for with ANDI) and clothing.

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