Taking stock of nationally determined contributions: Continued ratcheting of ambition is critical to limit global warming to 1.5°C

As countries take stock of progress made in accomplishing their climate goals ahead of COP28 this year, it is increasingly apparent that countries must ratchet ambition in policy areas such as non-CO2 gases and carbon dioxide removal, while halting deforestation to lead the globe on a path consistent with the goals of the Paris Agreement.

Deep near-term mitigation of short-lived climate forcers in Oman: grand challenges and prospects

Over time, short-lived climate forcers (SLCFs) have gradually gained prominence as a rationale in the international global mitigation strategy to preserve temperature below 1.5 °C by the end of this century. Scientists cite the short-term gains in air quality and health co-benefits associated with reducing SLCFs as grounds for raising the pressure on governments to eliminate SLCFs rapidly and aggressively. There is little research on whether deep SLCF mitigation during the next decade is feasible in low- and middle-income nations, particularly the hydrocarbon-based economy. This study estimates current and future emissions of potent SLCFs as methane (CH₄) hydrofluorocarbons (HFCs) in Oman using the basic tier 1 approach of the Intergovernmental Panel on Climate Change (IPCC) greenhouse gases (GHG) inventory Guidelines of 2006. Current and future emission of black carbon (BC) was also quantified using specific emission factors. A total of 38,268 Gg of SLFCs were released into the atmosphere in Oman in 2015, accounting for 38.8% of the country's total GHG emissions, and is expected to rise significantly over the next decade to reach 67,777 Gg by 2030. The analysis reveals that the source of Oman's highly potent SLCF emissions is associated with key and critical economic sectors such as the oil and gas industry, heavy road transportation, residential air conditioning (RAC), and industrial refrigeration. These vital economic sectors impose a "Grand Challenge" on the immediate reduction of SLCFs in Oman and the Gulf Cooperation Council (GCC). Accomplishing a rapid, significant reduction in highly potent SLCFs from the three challenging sectors over a 5- to 10-year time period does not appear feasible or realistic in the context of international market mechanisms, socioeconomic factors, and mitigation targets. Achieving a significant reduction in SLCFs for a hydrocarbon-based economy requires a profound economic shift. Creating an effective long-term vision for a post-oil economy over the next two decades provides a sound foundation for implementing economic and societal transformation policies incorporating near-zero-emission measures for the potent SLCFs.

Assessing synergies and trade-offs of diverging Paris-compliant mitigation strategies with long-term SDG objectives

The Sustainable Development Goals (SDGs) and the Paris Agreement are the two transformative agendas, which set the benchmarks for nations to address urgent social, economic and environmental challenges. Aside from setting long-term goals, the pathways followed by nations will involve a series of synergies and trade-offs both between and within these agendas. Since it will not be possible to optimise across the 17 SDGs while simultaneously transitioning to low-carbon societies, it will be necessary to implement policies to address the most critical aspects of the agendas and understand the implications for the other dimensions. Here, we rely on a modelling exercise to analyse the long-term implications of a variety of Paris-compliant mitigation strategies suggested in the recent scientific literature on multiple dimensions of the SDG Agenda. The strategies included rely on technological solutions such as renewable energy deployment or carbon capture and storage, nature-based solutions such as afforestation and behavioural changes in the demand side. Results for a selection of energy-environment SDGs suggest that some mitigation pathways could have negative implications on food and water prices, forest cover and increase pressure on water resources depending on the strategy followed, while renewable energy shares, household energy costs, ambient air pollution and yield impacts could be improved simultaneously while reducing greenhouse gas emissions. Overall, results indicate that promoting changes in the demand side could be beneficial to limit potential trade-offs.

Edge engineering on layered WS2 toward the electrocatalytic reduction of CO2: a first principles study

Transition-metal dichalcogenides (TMDCs) have been modified to show excellent electrocatalytic performance for the CO₂ reduction reaction (CO₂RR). However, little research has been reported on the edge modification of WS₂ and its electrocatalytic CO₂RR. In this work, the edge structure of WS₂ with W atoms exposed in the top layer was established by density functional theory calculations. Through using WS₂-xTM-y (x = 1, 2 or 3; y = 1 or 2; TM = Zn, Fe, Co or Ni) models by doping TM atoms on the top layer of WS₂, the effects of dopant species, doping concentration and adsorption sites on their electrocatalytic activity were investigated. Among the models, the active site for the CO₂RR is the W atoms. The doping of TM atoms would affect the bond strength between W and S atoms. After the doping of TM atoms in WS₂-2TM-1 ones, the electrical conduction of S atoms and the underlying W atoms can greatly be improved. Thus the catalytic activities can be significantly increased, in which the WS₂-2Zn-1 model shows the best catalytic activity. The limiting potential (U_L) of the CO₂RR to CO on the WS₂-2Zn-1 model is -0.51 V and the Gibbs energy change (ΔG) for the adsorption of intermediates on the WS₂-2Zn-1 model is ΔG(COOH*) = -0.37 and ΔG(CO*) = -0.51 eV, respectively. Solvation correction showed that WS₂-2Zn-1 could maintain good catalytic performance in a wide range of pH values. The present results may provide a theoretical basis for the design and synthesis of novel electrocatalysts with high performance for the CO₂RR.

From low carbon to carbon neutrality: A bibliometric analysis of the status, evolution and development trend

With global climate change becoming increasingly serious, carbon neutrality, a key strategy to mitigate climate change, has attracted widespread attention. However, due to the multidisciplinary and complexity of carbon neutrality studies, as well as the diversification of research content, a comprehensive review and systematic synthesis of which is quite limited. In this paper, a bibliometric analysis on the topic of carbon neutrality is conducted to reveal the research progress from a quantitative and visual perspective and describe the evolution of research hotspots. The results show that carbon neutrality research is abundant at both the macro and micro levels. Low carbon development is the premise of carbon neutrality, and emission reduction and carbon sinks are the basis of carbon neutrality. The degree of research varies significantly in different countries, with China dominating in the number of publications, followed by the USA and the UK. The realization of carbon neutrality cannot be fully achieved by one single perspective and requires a comprehensive and systematic analysis of technology, economy, and society. Carbon neutrality is a technology-driven process guided by policy. Economically, carbon taxes and carbon markets are two important market mechanisms for reducing carbon emissions. Technically, researches of negative carbon technologies and renewable energy are growing rapidly. Carbon market, carbon negative technology, circular economy, and green energy will become the focus of future research. This paper helps scholars to understand the overall state of carbon neutrality research and provides a historical reference for future research.

Ratcheting of climate pledges needed to limit peak global warming

The new and updated emission reduction pledges submitted by countries ahead of COP26 represent a meaningful strengthening of global ambition compared to the 2015 Paris pledges1,2. Yet, limiting global warming below 1.5°C this century will require countries to ratchet ambition for 2030 and beyond2-6. We explore a suite of emissions pathways in which countries ratchet and achieve ambition through a combination of increasing near-term ambition through 2030, accelerating post-2030 decarbonization, and advancing the dates for national net-zero pledges. We show that ratcheting near-term ambition through 2030 will be crucial to limiting peak temperature changes. Delaying ratcheting ambition to beyond 2030 could still deliver end-of-century temperature change of less than 1.5°C, but that would result in higher temperature overshoot over many decades with the potential for adverse consequences. Ratcheting near-term ambition would also deliver benefits from enhanced non-CO2 mitigation and facilitate faster transitions to net-zero emissions systems in major economies.

Decarbonizing the Global Economy—Investigating the Role of Carbon Emission Inertia Using the Integrated Assessment Model MIND

In 2015, the 21st Conference of the Parties reaffirmed the target of keeping the global mean temperature rise below 2 °C or 1.5 °C by 2100 while finding no consensus on how to decarbonize the global economy. In this regard, the speed of decarbonization reflects the (in)flexibility of transforming the energy sector due to engineering, political, or societal constraints. Using economy–energy–climate-integrated assessment models (IAMs), the maximum absolute rate of change in carbon emission allowed from each time step to the next, so-called carbon emission inertia (CEI), governs the magnitude of emission change, affecting investment decisions and economic welfare. Employing the model of investment and endogenous technological development (MIND), we conduct a cost-effectiveness analysis and examine anthropogenic global carbon emission scenarios in line with decarbonizing the global economy while measuring the global mean temperature. We examine the role of CEI as a crucial assumption, where the CEI can vary in four scenarios from 3.7% to 12.6% p.a. We provide what-if studies on global carbon emissions, global mean temperature change, and investments in renewable energy production and show that decarbonizing the global economy might still be possible before 2100 only if the CEI is high enough. In addition, we show that climate policy scenarios with early decarbonization and without negative emissions may still comply with the 2 °C target. However, our results indicate that the 1.5 °C target is not likely to be reached without negative emission technologies. Hence, the window of opportunity is beginning to close. This work can also assist to better interpret existing publications on various climate targets when altering CEI could have played a significant role.

Can updated climate pledges limit warming well below 2°C?

[Figure: see text].

Where is the EU headed given its current climate policy? A stakeholder-driven model inter-comparison

Recent calls to do climate policy research with, rather than for, stakeholders have been answered in non-modelling science. Notwithstanding progress in modelling literature, however, very little of the scenario space traces back to what stakeholders are ultimately concerned about. With a suite of eleven integrated assessment, energy system and sectoral models, we carry out a model inter-comparison for the EU, the scenario logic and research questions of which have been formulated based on stakeholders' concerns. The output of this process is a scenario framework exploring where the region is headed rather than how to achieve its goals, extrapolating its current policy efforts into the future. We find that Europe is currently on track to overperforming its pre-2020 40% target yet far from its newest ambition of 55% emissions cuts by 2030, as well as looking at a 1.0-2.35 GtCO₂ emissions range in 2050. Aside from the importance of transport electrification, deployment levels of carbon capture and storage are found intertwined with deeper emissions cuts and with hydrogen diffusion, with most hydrogen produced post-2040 being blue. Finally, the multi-model exercise has highlighted benefits from deeper decarbonisation in terms of energy security and jobs, and moderate to high renewables-dominated investment needs.

Effects of future climate change on birch abundance and their pollen load

Climate change impacts on the structure and function of ecosystems will worsen public health issues like allergic diseases. Birch trees (Betula spp.) are important sources of aeroallergens in Central and Northern Europe. Birches are vulnerable to climate change as these trees are sensitive to increased temperatures and summer droughts. This study aims to examine the effect of climate change on airborne birch pollen concentrations in Central Europe using Bavaria in Southern Germany as a case study. Pollen data from 28 monitoring stations in Bavaria were used in this study, with time series of up 30 years long. An integrative approach was used to model airborne birch pollen concentrations taking into account drivers influencing birch tree abundance and birch pollen production and projections made according to different climate change and socioeconomic scenarios. Birch tree abundance is projected to decrease in parts of Bavaria at different rates, depending on the climate scenario, particularly in current centres of the species distribution. Climate change is expected to result in initial increases in pollen load but, due to the reduction in birch trees, the amount of airborne birch pollen will decrease at lower altitudes. Conversely, higher altitude areas will experience expansions in birch tree distribution and subsequent increases in airborne birch pollen in the future. Even considering restrictions for migration rates, increases in pollen load are likely in Southwestern areas, where positive trends have already been detected during the last three decades. Integrating models for the distribution and abundance of pollen sources and the drivers that control birch pollen production allowed us to model airborne birch pollen concentrations in the future. The magnitude of changes depends on location and climate change scenario.

Study of the Kuznets environmental curve hypothesis from a global perspective 1960-2019: a semi-parametric panel data proposal

This work uses parametric and semiparametric panel data analysis methodologies to test the hypothesis of the environmental Kuznets curve, in 186 countries in the period 1960-2019. The main results reveal the acceptance of this hypothesis in the relationships of CO2 emissions (kt) and economic growth (GDP) and urbanization (% population) in the parametric models. Using semiparametric methods, the polynomial relations of fourth degree between CO2 emissions and GDP and of third degree between it and urbanization are verified. The economic policy implications derived from these results seem to indicate the need to continue making efforts in the reduction of CO2 emissions, through greater efforts in innovation and research and development, in search of clean and less polluting energies. The relationship between CO2 and economic growth is a major challenge, in terms of achieving a flattening of this relationship.

International Environmental Agreements and CO2 Emissions: Fresh Evidence from 11 Polluting Countries

This study attempts to evaluate the energy and carbon footprint within the framework of international environmental treaties and the efforts made by 11 large polluting countries to mitigate climate change. The econometric methodology accounts for the presence of cross-sectional dependence while it employs second-generation panel unit root tests and cointegrated relationships. To secure the robustness of our findings, we conduct an ARDL approach employing dynamic panel data techniques. Dynamic OLS is also applied to verify the validity of the empirical results. The empirical analysis supports that the reduction in CO2 emissions can be achieved without a slowdown in economic activity for the sample countries. The findings suggest insightful policy implications for policymakers and government officials.

Historical Variation of IEA Energy and CO2 Emission Projections: Implications for Future Energy Modeling

The World Energy Outlook reports produced by the International Energy Agency have long been considered the “gold standard” in terms of energy modeling and projecting future trends. It is thus extremely important to assess how well its projections are aligned with sustainable development goals as well as closely tracking observed, historical values. In this work we analyzed thirteen sets of World Energy Outlook projections from the last 25 years. Different scenarios were considered for the following regions and countries: world, OECD, OECD Europe, OECD North America, China, India, Russia, and Africa. The maximum variation between the projections for 2030 CO2 emissions from the energy sector, made between 2006 and 2018 for OECD, Europe and North America were found to be comparable with the gap between the Paris Agreement goals and the voluntary (unconditional) nationally determined contributions to remain below a 2 °C global temperature increase. For the same period, projections for the percentage of renewable electricity exhibited maximum variations between 51% and 96%, signaling a huge underestimation. We discuss the significance of overestimating energy demand and underestimating the rate of renewable energy implementation in the context of 2030 climate and energy policy targets, as well as desirable methodological changes to energy modeling under aggressive climate mitigation policies.

Assessing the effects of labor market dynamics on CO2 emissions in global value chains

International production fragmentation has led to substantial changes in labor market, such as job creation/job loss, changing labor market structure and labor productivity. Such changes are perceived to affect CO₂ emissions of those economies that participate in different parts of global value chains. This paper develops an accounting framework relating CO₂ emissions to labor market shaped by global value chains. It analyses the influential factors driving CO₂ emissions, and documents several pervasive empirical patterns. This is based on the recent environmental accounts developed by the European Commission and the World Input-Output Database over 2000-2014. The results show that the growth of CO₂ emissions is primarily reduced by intensity effect, followed by labor market structural change due to participation in value chains, while it is driven by labor productivity effect and job creation. In particular, the foreign job creation effect is mostly emission-increasing, even in those economies with shrinking domestic employment. These results highlight the role of labor market and global value chains in climate policymaking.

The Paris Climate Agreement and future sea-level rise from Antarctica

The Paris Agreement aims to limit global mean warming in the twenty-first century to less than 2 degrees Celsius above preindustrial levels, and to promote further efforts to limit warming to 1.5 degrees Celsius¹. The amount of greenhouse gas emissions in coming decades will be consequential for global mean sea level (GMSL) on century and longer timescales through a combination of ocean thermal expansion and loss of land ice². The Antarctic Ice Sheet (AIS) is Earth's largest land ice reservoir (equivalent to 57.9 metres of GMSL)³, and its ice loss is accelerating⁴. Extensive regions of the AIS are grounded below sea level and susceptible to dynamical instabilities^5-8 that are capable of producing very rapid retreat⁸. Yet the potential for the implementation of the Paris Agreement temperature targets to slow or stop the onset of these instabilities has not been directly tested with physics-based models. Here we use an observationally calibrated ice sheet-shelf model to show that with global warming limited to 2 degrees Celsius or less, Antarctic ice loss will continue at a pace similar to today's throughout the twenty-first century. However, scenarios more consistent with current policies (allowing 3 degrees Celsius of warming) give an abrupt jump in the pace of Antarctic ice loss after around 2060, contributing about 0.5 centimetres GMSL rise per year by 2100-an order of magnitude faster than today⁴. More fossil-fuel-intensive scenarios⁹ result in even greater acceleration. Ice-sheet retreat initiated by the thinning and loss of buttressing ice shelves continues for centuries, regardless of bedrock and sea-level feedback mechanisms^10-12 or geoengineered carbon dioxide reduction. These results demonstrate the possibility that rapid and unstoppable sea-level rise from Antarctica will be triggered if Paris Agreement targets are exceeded.

Oviductal fluid counterbalances the negative effect of high temperature on sperm in an ectotherm model

Global warming is affecting biodiversity; however, the extent to which animal reproductive processes respond to predicted temperature increments remains largely unexplored. The thermal environment has a pronounced impact on metabolic rates of ectotherms; therefore, an interesting question to assess is whether temperature increase might affect specific reproductive mechanisms like sperm performance in ectotherms. Moreover, in many species, oviductal fluid (OF) is known to regulate and maintain sperm quality; however, the role of OF in relation to the effects of high temperature on sperm remains unclear. Our aim was to experimentally test the effect of increased temperature on sperm velocity, swimming path and percentage of motility in neutral conditions at ejaculation (without OF) and in female's reproductive tract fluid (with OF), in a social ectotherm lizard model, Tropidurus spinulosus, which has specific thermal requirements for reproduction. Our results suggest that a rising temperature associated with global warming (+4°C) affects negatively sperm dynamics and survival. However, OF ameliorated the harmful effects of high temperature. This is an important point, as this study is the first to have tested the role of OF in preserving sperm from a warmer pre-fertilization environment. These results contribute to our understanding of how thermal environment changes might affect post-copulatory reproductive mechanisms. This article has an associated First Person interview with the first author of the paper.

A metric for spatially explicit contributions to science-based species targets

The Convention on Biological Diversity's post-2020 Global Biodiversity Framework will probably include a goal to stabilize and restore the status of species. Its delivery would be facilitated by making the actions required to halt and reverse species loss spatially explicit. Here, we develop a species threat abatement and restoration (STAR) metric that is scalable across species, threats and geographies. STAR quantifies the contributions that abating threats and restoring habitats in specific places offer towards reducing extinction risk. While every nation can contribute towards halting biodiversity loss, Indonesia, Colombia, Mexico, Madagascar and Brazil combined have stewardship over 31% of total STAR values for terrestrial amphibians, birds and mammals. Among actions, sustainable crop production and forestry dominate, contributing 41% of total STAR values for these taxonomic groups. Key Biodiversity Areas cover 9% of the terrestrial surface but capture 47% of STAR values. STAR could support governmental and non-state actors in quantifying their contributions to meeting science-based species targets within the framework.

Evaluating the economic impact of water scarcity in a changing world

Water scarcity is dynamic and complex, emerging from the combined influences of climate change, basin-level water resources, and managed systems’ adaptive capacities. Beyond geophysical stressors and responses, it is critical to also consider how multi-sector, multi-scale economic teleconnections mitigate or exacerbate water shortages. Here, we contribute a global-to-basin-scale exploratory analysis of potential water scarcity impacts by linking a global human-Earth system model, a global hydrologic model, and a metric for the loss of economic surplus due to resource shortages. We find that, dependent on scenario assumptions, major hydrologic basins can experience strongly positive or strongly negative economic impacts due to global trade dynamics and market adaptations to regional scarcity. In many cases, market adaptation profoundly magnifies economic uncertainty relative to hydrologic uncertainty. Our analysis finds that impactful scenarios are often combinations of standard scenarios, showcasing that planners cannot presume drivers of uncertainty in complex adaptive systems.

The impacts of water scarcity depend on physical basin characteristics and global economic dynamics. Here, the authors show scenario assumptions can yield either highly positive or negative economic impacts due to water scarcity, and the drivers of these impacts are basin-specific and cannot be determined a priori.

Impacts of long-term temperature change and variability on electricity investments

Long-term temperature change and variability are expected to have significant impacts on future electric capacity and investments. This study improves upon past studies by accounting for hourly and monthly dynamics of electricity use, long-term socioeconomic drivers, and interactions of the electric sector with rest of the economy for a comprehensive analysis of temperature change impacts on cooling and heating services and their corresponding impact on electric capacity and investments. Using the United States as an example, here we show that under a scenario consistent with a socioeconomic pathway 2 (SSP2) and representative concentration pathway 8.5 (RCP 8.5), mean temperature changes drive increases in annual electricity demands by 0.5-8% across states in 2100. But more importantly, peak temperature changes drive increases in capital investments by 3-22%. Moreover, temperature-induced capital investments are highly sensitive to both long-term socioeconomic assumptions and spatial heterogeneity of fuel prices and capital stock characteristics, which underscores the importance of a comprehensive approach to inform long-term electric sector planning.

The potential land requirements and related land use change emissions of solar energy

Although the transition to renewable energies will intensify the global competition for land, the potential impacts driven by solar energy remain unexplored. In this work, the potential solar land requirements and related land use change emissions are computed for the EU, India, Japan and South Korea. A novel method is developed within an integrated assessment model which links socioeconomic, energy, land and climate systems. At 25-80% penetration in the electricity mix of those regions by 2050, we find that solar energy may occupy 0.5-5% of total land. The resulting land cover changes, including indirect effects, will likely cause a net release of carbon ranging from 0 to 50 gCO₂/kWh, depending on the region, scale of expansion, solar technology efficiency and land management practices in solar parks. Hence, a coordinated planning and regulation of new solar energy infrastructures should be enforced to avoid a significant increase in their life cycle emissions through terrestrial carbon losses.

Mechanistic insights into carbon dioxide utilization by superoxide ion generated electrochemically in ionic liquid electrolyte

Understanding the reaction mechanism that controls the one-electron electrochemical reduction of oxygen is essential for sustainable use of the superoxide ion (O2˙-) during CO2 conversion. Here, stable generation of O2˙- in butyltrimethylammonium bis(trifluoromethylsulfonyl)imide [BMAmm+][TFSI-] ionic liquid (IL) was first detected at -0.823 V vs. Ag/AgCl using cyclic voltammetry (CV). The charge transfer coefficient associated with the process was ∼0.503. It was determined that [BMAmm+][TFSI-] is a task-specific IL with a large negative isovalue surface density accrued from the [BMAmm+] cation with negatively charged C(sp2) and C(sp3). Consequently, [BMAmm+][TFSI-] is less susceptible to the nucleophilic effect of O2˙- because only 8.4% O2˙- decay was recorded from 3 h long-term stability analysis. The CV analysis also detected that O2˙- mediated CO2 conversion in [BMAmm+][TFSI-] at -0.806 V vs. Ag/AgCl as seen by the disappearance of the oxidative faradaic current of O2˙-. Electrochemical impedance spectroscopy (EIS) detected the mechanism of O2˙- generation and CO2 conversion in [BMAmm+][TFSI-] for the first time. The EIS parameters in O2 saturated [BMAmm+][TFSI-] were different from those detected in O2/CO2 saturated [BMAmm+][TFSI-] or CO2 saturated [BMAmm+][TFSI-]. This was rationalized to be due to the formation of a [BMAmm+][TFSI-] film on the GC electrode, creating a 2.031 × 10-9 μF cm-2 double-layer capacitance (CDL). Therefore, during the O2˙- generation and CO2 utilization in [BMAmm+][TFSI-], the CDL increased to 5.897 μF cm-2 and 7.763 μF cm-2, respectively. The CO2 in [BMAmm+][TFSI-] was found to be highly unlikely to be electrochemically converted due to the high charge transfer resistance of 6.86 × 1018 kΩ. Subsequently, O2˙- directly mediated the CO2 conversion through a nucleophilic addition reaction pathway. These results offer new and sustainable opportunities for utilizing CO2 by reactive oxygen species in ionic liquid media.

Juliana A, Hartin C. Improving reduced complexity model assessment and usability

Reduced complexity climate models are useful tools with practical policy applications, yet evaluation of their performance and application is nascent. We call for stakeholder-driven development and assessment to address user needs, including provision of open-source code and guidance to inform model selection and application.

Pathway to Complete Energy Sector Decarbonization with Available Iridium Resources using Ultralow Loaded Water Electrolyzers

We present ultralow Ir-loaded (ULL) proton exchange membrane water electrolyzer (PEMWE) cells that can produce enough hydrogen to largely decarbonize the global natural gas, transportation, and electrical storage sectors by 2050, using only half of the annual global Ir production for PEMWE deployment. This represents a significant improvement in PEMWE's global potential, enabled by careful control of the anode catalyst layer (CL), including its mesostructure and catalyst dispersion. Using commercially relevant membranes (Nafion 117), cell materials, electrocatalysts, and fabrication techniques, we achieve at peak a 250× improvement in Ir mass activity over commercial PEMWEs. An optimal Ir loading of 0.011 mg_Ir cm^-2 operated at an Ir-specific power of ∼100 MW kg_Ir^-1 at a cell potential of ∼1.66 V versus RHE (85% higher heating value efficiency). We further evaluate the performance limitations within the ULL regime and offer new insights and guidance in CL design relevant to the broader energy conversion field.

The quest for improved air quality may push China to continue its CO2 reduction beyond the Paris Commitment

China is challenged with the simultaneous goals of improving air quality and mitigating climate change. The "Beautiful China" strategy, launched by the Chinese government in 2020, requires that all cities in China attain 35 μg/m³ or below for annual mean concentration of PM_2.5 (particulate matter with aerodynamic diameter less than 2.5 μm) by 2035. Meanwhile, China adopts a portfolio of low-carbon policies to meet its Nationally Determined Contribution (NDC) pledged in the Paris Agreement. Previous studies demonstrated the cobenefits to air pollution reduction from implementing low-carbon energy policies. Pathways for China to achieve dual targets of both air quality and CO₂ mitigation, however, have not been comprehensively explored. Here, we couple an integrated assessment model and an air quality model to evaluate air quality in China through 2035 under the NDC scenario and an alternative scenario (Co-Benefit Energy [CBE]) with enhanced low-carbon policies. Results indicate that some Chinese cities cannot meet the PM_2.5 target under the NDC scenario by 2035, even with the strictest end-of-pipe controls. Achieving the air quality target would require further reduction in emissions of multiple air pollutants by 6 to 32%, driving additional 22% reduction in CO₂ emissions relative to the NDC scenario. Results show that the incremental health benefit from improved air quality of CBE exceeds 8 times the additional costs of CO₂ mitigation, attributed particularly to the cost-effective reduction in household PM_2.5 exposure. The additional low-carbon energy polices required for China's air quality targets would lay an important foundation for its deep decarbonization aligned with the 2 °C global temperature target.

Rethinking electric vehicle subsidies, rediscovering energy efficiency

Existing regulations regarding fuel energy intensity (MJ/km, litres/100 km, or its inverse, miles per gallon) of light-duty vehicles (LDVs: cars, SUVs, and pickup trucks) for 2025 or 2030 either fall short of the longterm technical potential, or contain numerous loopholes that undermine their effectiveness. At the same time, governments are subsidizing the purchase of electric vehicles (EVs) while the market share of SUVs and pickup trucks grows. This paper reviews the feasible fuel and/or electricity energy intensity of LDVs, and argues that the severity of impending anthropogenic global warming merits a strong policy approach that (i) prescribes significant improvements in the energy intensity of non-electric LDVs and plugin hybrid EVs (PHEVs) when running on fuel, (ii) is independent of the number of electric vehicles sold, and (iii) is accompanied by an overall limit on fleet-average CO₂ emissions that applies to all manufacturers irrespective of the average size and mass of vehicles sold. Subsidies for EVs should be scaled back or eliminated, relying instead in the near term on deep across-the-board improvements in the fuel efficiency of LDVs that will have beneficial spillover effects on the eventual energy intensity of EVs and mineral requirements following a delayed market scale-up.

Implications of near-term mitigation on China's long-term energy transitions for aligning with the Paris goals

In the international community, there are many appeals to ratcheting up the current nationally determined contributions (NDCs), in order to narrow the 2030 global emissions gap with the Paris goals. Near-term mitigation has a direct impact on the required efforts beyond 2030 to control warming within 2°C or 1.5°C successfully. In this study, implications of near-term mitigation on China's long-term energy transitions until 2100 for aligning with the Paris goals, are quantified using a refined Global Change Assessment Model (GCAM) with six mitigation scenarios. Results show that intensifying near-term mitigation will alleviate China's transitional challenges during 2030-2050 and long-term reliance on carbon dioxide removal technologies (CDR). Each five-year earlier peaking of CO₂ allows almost a five-year later carbon neutrality of China's energy system. To align with 2°C (1.5°C), peaking in 2025 instead of 2030 reduces the requirement of CDR over the century by 17% (13%). Intensifying near-term mitigation also tends to have economic benefits to China's Paris-aligned energy transitions. Under 2°C (1.5°C), peaking in 2025 instead of 2030, with larger near-term mitigation costs by 1.3 (1.6) times, has the potential to reduce China's aggregate mitigation costs throughout the century by 4% (6%). Although in what way China's NDC is to be updated is determined by decision-makers, transitional and economic benefits suggest China to try its best to pursue more ambitious near-term mitigation in accordance with its latest national circumstances and development needs.

Climate Change and Public Policies in the Brazilian Amazon State of Mato Grosso: Perceptions and Challenges

This study examines how key stakeholders in agriculture in a number of municipalities in the Brazilian Amazon state of Mato Grosso are incorporating and adapting to public policies on climate change. Fieldwork and semi-structured interviews conducted in 2014 and 2018 with key stakeholders in the region were analyzed to assess the effectiveness of public policies incorporating climate change factors. Data obtained from documents from national institutions complemented these interviews. The results show that although local government claims that its mission is economic, social and sustainable development, and although public institutions and stakeholders repeat internationally recognized protocols and agreements in their communications, in actual fact, these are not reflected by any change in institutional behavior.

Impact of Climate Change on Olive Crop Production in Italy

The effects of climate change on agricultural systems raise important uncertainties about the future productivity and suitability of crops, especially in areas suffering from intense environmental changes. Olive groves occupy Mediterranean areas characterized by seasonal temporary droughts, which cause this cultivation to be highly dependent on local microclimatic conditions. Olive crop production can be reliably estimated using pollen intensity metrics together with post-pollination environmental conditions. In this study, we applied this kind of statistics-based models to identify the most relevant meteorological variables during the post-pollination periods for olive fruit production. Olive pollen time-series for the period of 1999–2012 was analyzed in 16 Italian provinces. Minimum and maximum temperature during spring and summer (March–August) showed a negative relationship with olive production, while precipitation always showed a positive correlation. The increase in aridity conditions observed in areas of Italy during the summer represents an important risk of decreasing olive crop production. The effect of climate change on the olive production trend is not clear because of the interactions between human and environmental factors, although some areas might show an increase in productivity in the near future under different climate change scenarios. However, as more drastic changes in temperature or precipitation take place, the risk to olive production will be considerably greater.

Self-preservation strategy for approaching global warming targets in the post-Paris Agreement era

A strategy that informs on countries’ potential losses due to lack of climate action may facilitate global climate governance. Here, we quantify a distribution of mitigation effort whereby each country is economically better off than under current climate pledges. This effort-sharing optimizing approach applied to a 1.5 °C and 2 °C global warming threshold suggests self-preservation emissions trajectories to inform NDCs enhancement and long-term strategies. Results show that following the current emissions reduction efforts, the whole world would experience a washout of benefit, amounting to almost 126.68–616.12 trillion dollars until 2100 compared to 1.5 °C or well below 2 °C commensurate action. If countries are even unable to implement their current NDCs, the whole world would lose more benefit, almost 149.78–791.98 trillion dollars until 2100. On the contrary, all countries will be able to have a significant positive cumulative net income before 2100 if they follow the self-preservation strategy.

The emission allocation strategies of global scenarios do not specify the potential benefits from extra climate mitigation efforts. Here the authors show that compared to the current Nationally Distributed Contributions, the proposed self-preservation strategy might generate 126–616 trillion dollars of additional benefits by 2100.

Could congressionally mandated incentives lead to deployment of large-scale CO2 capture, facilities for enhanced oil recovery CO2 markets and geologic CO2 storage?

In passing the Bipartisan Budget Act of 2018, Congress reformed and strengthened a section of the tax code, 45Q, which provides tax credits of up to $35/ton CO₂ for the capture and utilization of CO₂ in qualifying applications such as enhanced oil recovery (EOR) and up to $50/ton CO₂ for CO₂ that is captured and permanently stored in a geologic repository. Earlier versions of the tax credit with lower credit values generated limited interest. This change to the tax code could potentially alter U.S. energy systems. This paper examines the effect of the increased 45Q credits on CO₂ capture, utilization and storage (CCUS) deployment in the United States and on petroleum and power production. A range of potential outcomes is explored using five modeling tools. The paper goes on to explore the potential impact of possible modifications of the current tax credit including extension of its availability in time, the period over which 45Q tax credits can be utilized for any given asset and increases in the value of the credit as well as interactions with technology availability and carbon taxation. The paper concludes that 45Q tax credits could stimulate additional CCUS beyond that which is already underway.

State-level drivers of future fine particulate matter mortality in the United States

Future fine particulate matter (PM₂.₅) concentrations and resulting health impacts will be largely determined by factors such as energy use, fuel choices, emission controls, state and national policies, and demographcs. In this study, a human-earth system model is used to estimate PM_2.5 mortality costs (PMMC) due to air pollutant emissions from each US state over the period 2015 to 2050, considering current major air quality and energy regulations. Contributions of various socioeconomic and energy factors to PMMC are quantified using the Logarithmic Mean Divisia Index. National PMMC are estimated to decrease 25% from 2015 to 2050, driven by decreases in energy intensity and PMMC per unit consumption of electric sector coal and transportation liquids. These factors together contribute 68% of the decrease, primarily from technology improvements and air quality regulations. States with greater population and economic growth, but with fewer clean energy resources, are more likely to face significant challenges in reducing future PMMC from their emissions. In contrast, states with larger projected decreases in PMMC have smaller increases in population and per capita GDP, and greater decreases in electric sector coal share and PMMC per unit fuel consumption.

Pollutant gas and particulate material emissions in ethanol production in Brazil: social and environmental impacts

The replacement of fossil-based fuels by renewable fuels (biofuels) was proposed in the IPCC report, as an alternative to reduce greenhouse gas emission and reach out to a low-carbon economy. On this perspective, the Brazilian government had implemented a renewable energy program based on the use of ethanol in the transport sector. This work evaluates the scenario of pollutant gas emissions and particulate material that comes from the biomass burning process involved in ethanol production cycle, in the city of Campos dos Goytacazes, Brazil. The gases and particulate material emitted by sugarcane and bagasse burning processes-the last one in energy co-generation mills-were analyzed. A laboratory-controlled burning of both samples was realized in an oven with temperature ramp from 250 to 400 °C, at a regular rate of 50 °C. The gas samples were collected directly from the oven's exhaust pipe. The particulates obtained were the residual material taken out of the burned samples: a powder with the aspect of soot. A photoacoustic spectroscopy system coupled with quantum cascade laser and electrochemical analyzers was used to measure the emission of polluting gases such as N₂O, CO₂, CO, NO_x (NO, NO₂), and SO₂ in ppmv range. Fluorescent X-ray spectrometry was applied to evaluate the chemical composition of particulate material, enabling the identification of elements such as Si, Al, Ca, K, Fe, S, P, Ti, Mn, Cu, Zn, Sc, V, Cu, and Sr.

Reducing carbon dioxide emissions; Does renewable energy matter?

The study employed panel cointegration techniques to investigate the relationship between renewable energy and carbon dioxide emissions for 28 Sub-Sahara African countries spanning the period 1980-2014. The findings based on the Fully Modified OLS and GMM estimation techniques show that both renewable and nonrenewable energy contribute to carbon dioxide emissions in the countries studied in the long run but only nonrenewable energy has a significant positive effect on carbon dioxide emissions in the short run. The results show that a percentage increase in nonrenewable energy consumption leads to an increase of 1.07% and 1.9% in CO₂ emissions in the short and long run respectively. Additionally, economic growth contributes to environmental degradation while urbanization has a negative effect on carbon dioxide emissions. A percentage increase in GDP leads to 1.3% and 1.82% increase in emissions in the short and long run respectively. The results also show that less democratic states are more likely to pollute the environment than more democratic states. Further, there is no statistically significant effect of non-renewable energy in the short-run for more democratic nations.

Can China Peak Its Non-CO2 GHG Emissions before 2030 by Implementing Its Nationally Determined Contribution?

Non-CO₂ greenhouse gas (GHG) emissions account for about ¹/₄ of global GHG emissions, and the trend of these emissions, as well as their mitigation potential and abatement cost, are of interest to both scientific researchers and decision makers. We present an integrated model, China Multigas Optimal Reduction Evaluation model (China-MORE), of the nitrous oxide (N₂O), methane (CH₄), and fluorinated gases (F-gases) emissions of China, with which we analyze the non-CO₂ emission reduction implications of China's Paris pledges. We find that China's non-CO₂ emissions can peak before 2030 under its Paris pledges, where the cobenefit of coal control policy is the largest contributor to this emissions trajectory due to reduction of CH₄ from coal mines. Based on the mitigation cost curve, we show that while the non-CO₂ emission reductions are cost-effective at a lower reduction rate, they can only be reduced up to 60-70% due to physical constraints of the reduction technologies, leaving 1.4 Gt CO₂-eq of residual emissions in 2050. The growth of non-CO₂ emissions in China is largely driven by household consumption of cooling technologies, vehicles, and food. Our findings imply that deep reductions can only be achieved through the deployment of mitigation technologies at a reasonable cost, along with policies to induce behavioral change.

Quantifying operational lifetimes for coal power plants under the Paris goals

A rapid transition away from unabated coal use is essential to fulfilling the Paris climate goals. However, many countries are actively building and operating coal power plants. Here we use plant-level data to specify alternative trajectories for coal technologies in an integrated assessment model. We then quantify cost-effective retirement pathways for global and country-level coal fleets to limit long-term temperature change. We present our results using a decision-relevant metric: the operational lifetime limit. Even if no new plants are built, the lifetimes of existing units are reduced to approximately 35 years in a well-below 2 °C scenario or 20 years in a 1.5 °C scenario. The risk of continued coal expansion, including the near-term growth permitted in some Nationally Determined Contributions (NDCs), is large. The lifetime limits for both 2 °C and 1.5 °C are reduced by 5 years if plants under construction come online and 10 years if all proposed projects are built.

Electrochemical CO2 Reduction into Chemical Feedstocks: From Mechanistic Electrocatalysis Models to System Design

The electrochemical reduction of CO₂ is a promising route to convert intermittent renewable energy to storable fuels and valuable chemical feedstocks. To scale this technology for industrial implementation, a deepened understanding of how the CO₂ reduction reaction (CO₂ RR) proceeds will help converge on optimal operating parameters. Here, a techno-economic analysis is presented with the goal of identifying maximally profitable products and the performance targets that must be met to ensure economic viability-metrics that include current density, Faradaic efficiency, energy efficiency, and stability. The latest computational understanding of the CO₂ RR is discussed along with how this can contribute to the rational design of efficient, selective, and stable electrocatalysts. Catalyst materials are classified according to their selectivity for products of interest and their potential to achieve performance targets is assessed. The recent progress and opportunities in system design for CO₂ electroreduction are described. To conclude, the remaining technological challenges are highlighted, suggesting full-cell energy efficiency as a guiding performance metric for industrial impact.

Regional Temperature Response in Central Asia to National Committed Emission Reductions

National committed greenhouse gas emission reduction actions are the center of the Paris Agreement, and are known as 'Intended Nationally Determined Contributions' (INDC) that aim to slow down global warming. The climate response to INDC emission reduction is a focus in climate change science. In this study, data from 32 global climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) were applied to investigate the changes in the mean and extreme high temperatures in Central Asia (CA) under the INDC scenario above the present-day level. The results show that the magnitude of warming in CA is remarkably higher than the global mean. Almost all the regions in CA will experience more intense, more frequent, and longer-lasting extreme high-temperature events. In comparison with the INDC scenario, the reduced warming of the 2.0 °C/1.5 °C target scenarios will help avoid approximately 44-61%/65-80% of the increase in extreme temperature events in terms of the intensity, frequency, and duration in CA. These results contribute to an improved understanding of the benefits of limiting global warming to the 2.0 °C/1.5 °C targets, which is paramount for mitigation and adaptation planning.

Influences of 1.5 °C and 2.0 °C global warming scenarios on water use efficiency dynamics in the sandy areas of northern China

Water use efficiency (WUE) is an important variable used in hydrometeorology study to reveal the links between carbon-water cycles in sandy ecosystems which are highly sensitive to climate change and can readily reflect the effects of it. In light of the Paris Agreement, it is essential to identify the regional impacts of 0.5 °C of additional global warming to inform climate adaptation and mitigation strategies. Using the modified Carnegie-Ames-Stanford Approach (CASA) and Advection-Aridity (AA) models with global warming values of 1.5 °C and 2.0 °C above preindustrial levels from Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2b) datasets, we conducted a new set of climate simulations to assess the effects of climate on WUE (the ratio of net primary productivity (NPP) to actual evapotranspiration (ETa)) in different sandy land types (mobile sandy land, MSL; semimobile/semifixed sandy land, SMSF; and fixed sandy land, FSL) during the period of baseline (1986-2005) and future (2006-2100). The spatiotemporal patterns of ETa, NPP, and WUE mostly showed increasing trends; the value of WUE decreased (6.40%) only in MSL with an additional 0.5 °C of warming. Meteorological and vegetation factors determined the variations in WUE. With warming, only the correlation between precipitation and WUE decreased in the three sandy land types, and the leaf area index (LAI) increased with an additional 0.5 °C of warming. The desertification degree comprehensively reflects the linkages among the standardized precipitation evapotranspiration index (SPEI), LAI and WUE. Simulation results indicated the sandy area extent could potential increase by 20 × 10⁴ km² per decade on average during 2016-2047 and that the increase could be gradual (2.60 × 10⁴ km² per decade) after 2050 (2050-2100). These results highlight the benefits of limiting the global mean temperature change to 1.5 °C above preindustrial levels and can help identify the risk of desertification with an additional 0.5 °C of warming.

The Paris pledges and the energy-water-land nexus in Latin America: Exploring implications of greenhouse gas emission reductions

In the 2015 Paris Agreement, nations worldwide pledged emissions reductions (Nationally Determined Contributions-NDCs) to avert the threat of climate change, and agreed to periodically review these pledges to strengthen their level of ambition. Previous studies have analyzed NDCs largely in terms of their implied contribution to limit global warming, their implications on the energy sector or on mitigation costs. Nevertheless, a gap in the literature exists regarding the understanding of implications of the NDCs on countries' Energy-Water-Land nexus resource systems. The present paper explores this angle within the regional context of Latin America by employing the Global Change Assessment Model, a state-of-the-art integrated assessment model capable of representing key system-wide interactions among nexus sectors and mitigation policies. By focusing on Brazil, Mexico, Argentina and Colombia, we stress potential implications on national-level water demands depending on countries' strategies to enforce energy-related emissions reductions and their interplays with the land sector. Despite the differential implications of the Paris pledges on each country, increased water demands for crop and biomass irrigation and for electricity generation stand out as potential trade-offs that may emerge under the NDC policy. Hence, this study underscores the need of considering a nexus resource planning framework (known as "Nexus Approach") in the forthcoming NDCs updating cycles as a mean to contribute toward sustainable development.

Climate damages and adaptation potential across diverse sectors of the United States

There is a growing capability to project the impacts and economic effects of climate change across multiple sectors. This information is needed to inform decisions regarding the diversity and magnitude of future climate impacts and explore how mitigation and adaptation actions might affect these risks. Here, we summarize results from sectoral impact models applied within a consistent modelling framework to project how climate change will affect 22 impact sectors of the United States, including effects on human health, infrastructure and agriculture. The results show complex patterns of projected changes across the country, with damages in some sectors (for example, labour, extreme temperature mortality and coastal property) estimated to range in the hundreds of billions of US dollars annually by the end of the century under high emissions. Inclusion of a large number of sectors shows that there are no regions that escape some mix of adverse impacts. Lower emissions, and adaptation in relevant sectors, would result in substantial economic benefits.

Case for equity between Paris Climate agreement's Co-benefits and adaptation

There are heightened debates on limited opportunity of the global adaptation policy goals of the Paris Climate Agreement (PaCA) to match efforts at mitigation and adaptation. This has been attributed partially to the overstatement in Article 7 Paragraph 4 of the PaCA that "greater levels of mitigation" reduces the cost of additional adaptation through mitigation Co-benefits. Therefore, the paper explores how Article 7 of the PaCA partially faults the natural synergy between mitigation and adaptation to equally reduce aggregate emission, although mitigation could help reduce adaptation to physical exposure. Co-benefits are non-climate ancillary benefits from emission reduction that is human-centered. Article 7 of the PaCA overtly favors efforts at mitigation compared to adaptation, yet how much mitigation benefits match adaptation cost including human dimension issues remain speculative and also constrained emission leakages. Thus, the sole attribution of avoiding additional adaptation cost to increased mitigation efforts is far from the reality as adaptation could offset its own additional cost through benefits that reduce emissions, and synonymous to mitigation Co-benefits. For example, the adaptation intentions of ecosystem-based adaptation (Eba), urban NEXUS, integrated water resources management (IWRM) and climate smart agriculture (CSA) in aspects of biodiversity conservation, energy redistribution from human activity, water purification and nutrient recycling are also major sources of emission sink. Therefore, the Article 7 of the PaCA could be enhanced by broadening the definition of Co-benefits to reflect the two-way equity-bound efforts at mitigation and adaptation towards reduced emission leakages and additional adaptation cost.

Half a degree and rapid socioeconomic development matter for heatwave risk

While every society can be exposed to heatwaves, some people suffer far less harm and recover more quickly than others from their occurrence. Here we project indicators of global heatwave risk associated with global warming of 1.5 and 2 °C, specified by the Paris agreement, for two future pathways of societal development representing low and high vulnerability conditions. Results suggest that at the 1.5 °C warming level, heatwave exposure in 2075 estimated for the population living in low development countries is expected to be greater than exposure at the warming level of 2 °C for the population living in very high development countries. A similar result holds for an illustrative heatwave risk index. However, the projected difference in heatwave exposure and the illustrative risk index for the low and very high development countries will be significantly reduced if global warming is stabilized below 1.5 °C, and in the presence of rapid social development.

Climate extremes, exposure and vulnerability all contribute to global difference in heatwave risk. Here the authors investigated the inequality in global heatwave risk under both 1.5 and 2 °C scenarios and found that heatwave risk for the poor under 1.5 °C scenario exceeds that risk for the rich under 2 °C scenario.

Social science perspectives on drivers of and responses to global climate change

This article provides a review of recent anthropological, archeological, geographical, and sociological research on anthropogenic drivers of climate change, with a particular focus on drivers of carbon emissions, mitigation and adaptation. The four disciplines emphasize cultural, economic, geographic, historical, political, and social-structural factors to be important drivers of and responses to climate change. Each of these disciplines has unique perspectives and makes noteworthy contributions to our shared understanding of anthropogenic drivers, but they also complement one another and contribute to integrated, multidisciplinary frameworks. The article begins with discussions of research on temporal dimensions of human drivers of carbon emissions, highlighting interactions between long-term and near-term drivers. Next, descriptions of the disciplines' contributions to the understanding of mitigation and adaptation are provided. It concludes with a summary of key lessons offered by the four disciplines as well as suggestions for future research. This article is categorized under: Climate Economics > Economics and Climate Change.

Evaluating climate geoengineering proposals in the context of the Paris Agreement temperature goals

Current mitigation efforts and existing future commitments are inadequate to accomplish the Paris Agreement temperature goals. In light of this, research and debate are intensifying on the possibilities of additionally employing proposed climate geoengineering technologies, either through atmospheric carbon dioxide removal or farther-reaching interventions altering the Earth’s radiative energy budget. Although research indicates that several techniques may eventually have the physical potential to contribute to limiting climate change, all are in early stages of development, involve substantial uncertainties and risks, and raise ethical and governance dilemmas. Based on present knowledge, climate geoengineering techniques cannot be relied on to significantly contribute to meeting the Paris Agreement temperature goals.

Research and debate are intensifying on complementing CO₂ emissions reductions with hypothetical climate geoengineering techniques. Here, the authors assess their potentials, uncertainties and risks, and show that they cannot yet be relied on to significantly contribute to meeting the Paris Agreement temperature goals.

Nuclear energy: Between global electricity demand, worldwide decarbonisation imperativeness, and planetary environmental implications

For decades, nuclear energy has been considered an important option for ensuring global energy security, and it has recently started being promoted as a solution for climate change mitigation. However, nuclear power remains highly controversial due to its associated risks - nuclear accidents and problematic radioactive waste management. This review aims to assess the viability of global nuclear energy economically (energy-wise), climatically and environmentally. To this end, the nuclear sector's energy- and climate-related advantages were explored alongside the downsides that mainly relate to radioactive pollution. Economically, it was found that nuclear energy is still an important power source in many countries around the world. Climatically, nuclear power is a low-carbon technology and can therefore be a viable option for the decarbonization of the world's major economies over the following decades, if coupled with other large-scale strategies such as renewable energies. These benefits are however outweighed by the radioactive danger associated to nuclear power plants, either in the context of the nuclear accidents that have already occurred or in that of the large amounts of long-lived nuclear waste that have been growing for decades and that represent a significant environmental and societal threat.

Health co-benefits from air pollution and mitigation costs of the Paris Agreement: a modelling study

BACKGROUND

Although the co-benefits from addressing problems related to both climate change and air pollution have been recognised, there is not much evidence comparing the mitigation costs and economic benefits of air pollution reduction for alternative approaches to meeting greenhouse gas targets. We analysed the extent to which health co-benefits would compensate the mitigation cost of achieving the targets of the Paris climate agreement (2°C and 1·5°C) under different scenarios in which the emissions abatement effort is shared between countries in accordance with three established equity criteria.

METHODS

Our study had three stages. First, we used an integrated assessment model, the Global Change Assessment Model (GCAM), to investigate the emission (greenhouse gases and air pollutants) pathways and abatement costs of a set of scenarios with varying temperature objectives (nationally determined contributions, 2°C, or 1·5°C) and approaches to the distribution of climate change methods (capability, constant emission ratios, and equal per capita). The resulting emissions pathways were transferred to an air quality model (TM5-FASST) to estimate the concentrations of particulate matter and ozone in the atmosphere and the resulting associated premature deaths and morbidity. We then applied a monetary value to these health impacts by use of a term called the value of statistical life and compared these values with those of the mitigation costs calculated from GCAM, both globally and regionally. Our analysis looked forward to 2050 in accordance with the socioeconomic narrative Shared Socioeconomic Pathways 2.

FINDINGS

The health co-benefits substantially outweighed the policy cost of achieving the target for all of the scenarios that we analysed. In some of the mitigation strategies, the median co-benefits were double the median costs at a global level. The ratio of health co-benefit to mitigation cost ranged from 1·4 to 2·45, depending on the scenario. At the regional level, the costs of reducing greenhouse gas emissions could be compensated with the health co-benefits alone for China and India, whereas the proportion the co-benefits covered varied but could be substantial in the European Union (7-84%) and USA (10-41%), respectively. Finally, we found that the extra effort of trying to pursue the 1·5°C target instead of the 2°C target would generate a substantial net benefit in India (US$3·28-8·4 trillion) and China ($0·27-2·31 trillion), although this positive result was not seen in the other regions.

INTERPRETATION

Substantial health gains can be achieved from taking action to prevent climate change, independent of any future reductions in damages due to climate change. Some countries, such as China and India, could justify stringent mitigation efforts just by including health co-benefits in the analysis. Our results also suggest that the statement in the Paris Agreement to pursue efforts to limit temperature increase to 1·5°C could make economic sense in some scenarios and countries if health co-benefits are taken into account.

FUNDING

European Union's Horizon 2020 research and innovation programme.