Global Mean Temperature Rise Research Articles

Radiative forcing geoengineering under high CO2 levels leads to higher risk of Arctic wildfires and permafrost thaw than a targeted mitigation scenario

Radiative forcing geoengineering is discussed as an intermediate solution to partially offset greenhouse gas-driven warming by altering the Earth’s energy budget. Here we use an Earth System Model to analyse the response in Arctic temperatures to radiative geoengineering applied under the representative concentration pathway 8.5 to decrease the radiative forcing to that achieved under the representative concentration pathway 4.5. The three methods Stratospheric Aerosol Injection, Marine Cloud Brightening, and Cirrus Cloud Thinning, mitigate the global mean temperature rise, however, under our experimental designs, the projected Arctic temperatures are higher than if the same temperature was achieved under emission mitigation. The maximum temperature increase under Cirrus Cloud Thinning and Marine Cloud Brightening is linked to carbon dioxide plant physiological forcing, shifting the system into climatic conditions favouring the development of fires. Under Stratospheric Aerosol Injection, the Arctic land with temperatures permanently below freezing decreased by 7.8% compared to the representative concentration pathway 4.5. This study concludes that these specific radiative forcing geoengineering designs induce less efficient cooling of the Arctic than the global mean and worsen extreme conditions compared to the representative concentration pathway 4.5.

The potential environmental and climate impacts of stratospheric aerosol injection: a review

This article reviews scientific evidence for the potential environmental impacts of stratospheric aerosol injection, a form of solar radiation geoengineering.

Effects of multi-observations uncertainty and models similarity on climate change projections

Climate change projections (CCPs) are based on the multimodel means of individual climate model simulations that are assumed to be independent. However, model similarity leads to projections biased toward the largest set of similar models and intermodel uncertainty underestimation. We assessed the influences of similarities in CMIP6 through CMIP3 CCPs. We ascertained model similarity from shared physics/dynamics and initial conditions by comparing simulated spatial temperature and precipitation with the corresponding observed patterns and accounting for intermodel spread relative to the observational uncertainty, which is also critical. After accounting for similarity, the information from 57 CMIP6, 47 CMIP5, and 24 CMIP3 models can be explained by just 11 independent models without significant differences in globally averaged climate change statistics. On average, independent models indicate a lower global-mean temperature rise of 0.25 °C (~0.5 °C–1 °C in some regions) relative to all models by the end of the 21st century under CMIP6’s highest emission scenario.

Change in cooling degree days with global mean temperature rise increasing from 1.5 °C to 2.0 °C

AbstractLimiting global mean temperature rise to 1.5 °C is increasingly out of reach. Here we show the impact on global cooling demand in moving from 1.5 °C to 2.0 °C of global warming. African countries have the highest increase in cooling requirements. Switzerland, the United Kingdom and Norway (traditionally unprepared for heat) will suffer the largest relative cooling demand surges. Immediate and unprecedented adaptation interventions are required worldwide to be prepared for a hotter world.

International planetary sunshade concept with a function-integrated and scalable support structure based on coreless filament winding

Despite all current efforts, climate change is the greatest challenge of the 21st century. Since existing measures will fail to prevent critical tipping points from being reached, in addition to terrestrial geoengineering methods, efforts are underway to explore new ways to implement space-based geoengineering methods into the short-term construction of a buffer solution - the International Planetary Sunshade (IPSS). The IPSS system reduces solar irradiation mitigating the global mean temperature rise while offering a sustainable energy supply. The developement of the system poses multifaceted challenges only to be mastered by a collaboration of space agencies and private companies, while supported by society. Therefore, tackling the IPSS within international roadmaps is essential to exploit synergies, shorten development time, and promote international cooperation. An evolutionary concept achieves stepwise Earth independence by utilizing lunar resources. The feasibility of the IPSS also depends on the foil’s supporting structure. Therefore, a lightweight manufacturing technology that meets several criteria, such as scalability, adaptivity, material compatibility, full automation, on-orbit manufacturing, in-situ resource utilization, and digital design including function integration, must be adopted. Hence, coreless filament winding (CFW) may be a suitable technology for realizing the demanded mass savings. The prerequisite for the superiority of CFW structures is an application- and material-compliant component and fiber net design. Previous experience with CFW cannot be directly transferred to the IPSS system due to the changed requirements for space application. This paper will present a systematic design concept for the IPSS, initially exploring a CFW support structure by discussing segmentation and modularity, proposing a new connection system, and implementing function integration.

Quantifying the contribution of major carbon producers to increases in vapor pressure deficit and burned area in western US and southwestern Canadian forests

Increases in burned forest area across the western United States and southwestern Canada over the last several decades have been partially driven by a rise in vapor pressure deficit (VPD), a measure of the atmosphere’s drying power that is significantly influenced by human-caused climate change. Previous research has quantified the contribution of carbon emissions traced back to a set of 88 major fossil fuel producers and cement manufacturers to historical global mean temperature rise. In this study, we extend that research into the domain of forest fires. We use a global energy balance carbon-cycle model, a suite of climate models, and a burned area (BA) model to determine the contribution of emissions traced to the major carbon producers to the long-term increase in VPD during 1901–2021 and to cumulative forest fire area during 1986–2021 in the western US and southwestern Canada. Based on climate model data, we find that emissions traced to these carbon producers contributed 48% (interquartile range (IQR) 38%–63%) of the long-term rise in VPD between 1901 and 2021. BA modeling indicates that these emissions also contributed 37% (IQR 26%–47%) of the cumulative area burned by forest fires between 1986 and 2021 in the western US and southwestern Canada. The increase in VPD in this region is linked to both increased fire activity and the region’s current and prolonged megadrought. As loss and damage from these hazards mounts, this research can inform public and legal dialogues regarding the responsibility carbon producers bear for addressing past, present, and future climate risks associated with fires and drought in the western US and southwestern Canada.

Assessment of Meteorological and Agricultural Drought Indices under Climate Change Scenarios in the South Saskatchewan River Basin, Canada

Climate change has amplified the severity of droughts with potentially adverse impacts on agriculture in western Canada. This study assessed meteorological and agricultural drought in the Southern Saskatchewan River Basin (SSRB) using an array of drought indices, including the Standardized Precipitation Index (SPI), the Standardized Precipitation-Evapotranspiration Index (SPEI), the Self-Calibrated Palmer Drought Severity Index (scPDSI), the Soil Moisture Deficit Index (SMDI), and the Evapotranspiration Deficit Index (ETDI). These indices were evaluated using multiple regional climate model (RCM) projections assuming 1.5, 2.0, and 3.0 °C thresholds of global warming. A modified Soil and Water Assessment Tool (SWAT-M) was used to simulate the soil water content (SWC), actual evapotranspiration (AET), and potential evapotranspiration. The results of a sensitivity analysis using the SUFI-2 method in SWAT-CUP showed that the model performed well with BIAS lower than 10% and NSE and R higher than 0.7, and the range of SWC output closely matched the observed SWC. According to the RCM projections, the annual precipitation increases for all three global temperature thresholds while the annual mean temperature increases at a greater rate than the rise in global mean temperature. The projected PDSI and the SPEI suggest that drought duration and severity will exceed historical values while SPI will remain largely unchanged. Furthermore, severe drought conditions (SMDI < 2.0) are more frequent under the 3.0 °C global temperature scenario. The mean ETDI was historically 0.58 while the projected value is 0.2, 0.1, and −0.2 for the first to third scenarios, respectively. Simulated values, spatial maps, and heat maps of SMDI and ETDI illustrated that Canesm2.CRCM5 projects the driest conditions among all the RCMs. Agricultural drought indices, which incorporate SWC data, show more significant effects than meteorological drought indices. The increasing dryness will potentially impact agricultural crop production, particularly under the third scenario (3 °C) in the SSRB.

Five U.S. Dietary Patterns and Their Relationship to Land Use, Water Use, and Greenhouse Gas Emissions: Implications for Future Food Security.

The U.S. agri-food system is a driver of climate change and other impacts. In order to achieve environmental targets that limit global mean temperature rise ≤2 °C, a shift in American dietary patterns is critical. The purpose of this study was twofold: (1) to determine the environmental impact (i.e., land use, water use, and GHG emissions) related to consumption of five U.S. dietary patterns (i.e., Current U.S., the Healthy U.S., Mediterranean, Healthy Vegetarian, and Vegan), and (2) to determine the specific impact of each food group in each dietary pattern on the three environmental indicators. This study utilized existing datasets to synthesize information related to the study's environmental indicators and food production and connected these data to the current U.S. diet and the USDA-defined diets. Results indicate that the three omnivore diets contributed the greatest to GHG emissions, land use and water use. The Vegan diet scored the lowest across all indicators, although the water required for plant-based protein nearly offset other water gains. For the omnivore diets, red meat and dairy milk contributed the most to each environmental indicator. By considering sustainability as well as health outcomes in their recommendations in the Dietary Guidelines, the USDA can have a critical role in shifting diets necessary to alter climate change trends.

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.

Declining greenhouse gas emissions in the US diet (2003–2018): Drivers and demographic trends

The food system is a major driver of climate change, and many have noted that a shift in consumption patterns is necessary to achieve greenhouse gas (GHG) emission reduction targets that can limit global mean temperature rise ≤2 °C. Beef is the largest GHG emitting commodity in the United States, and in recent years national consumption has been declining. Little is understood about how this change in consumption and other dietary trends have influenced the overall GHGs associated with the US diet. The objective of this study is to estimate the GHGs of changing dietary patterns from individual self-selected diets in the United States from 2003 to 2018 and evaluate trends and potential disparities among demographic subgroups. Life cycle emissions factors (representing food production impacts) for food commodities from dataFIELD were used to estimate GHGs associated with food items described by US adults (>20 years, n = 39,750) in the National Health and Nutrition Examination Survey (NHANES). From 2003 to 2018, the mean GHG emissions associated with the US diet fell by more than 35%, from 4.02 kg CO2e per day per capita, to 2.45 kg CO2e per day per capita, despite average caloric intake remaining relatively stable over the same period. Average beef consumption declined 40% per capita over the study period, which contributed to more than 50% of the observed GHG savings in the diet over the study period. All demographic variables included in this analysis (age, gender, race/ethnicity, and ratio of family income to the federal poverty level) exhibited a reduction in GHG emissions associated with their diets. However, GHGs and overall rate of change differed across demographic subgroups. Black women had the lowest GHG emissions associated with their diet, 1.92 kg CO2e per capita per day. Men aged 20–34 had the largest rate of reduction in GHGs associated with diet changes, with an average annual decline of 210g CO2e per day per capita over the study period. Despite GHGs associated with the US diet falling over the last 15 years, the US diet is still exceeding established GHG limits to meet global targets, such as the Paris Agreement. Additional research is needed to better understand motivations and drivers that have reduced emissions in the diet over this period, particularly in demographic subgroups that showed both low impact and a rapid decline in emissions.

Carbon tax as the most appropriate carbon pricing mechanism for developing countries and strategies to design an effective policy

<abstract> <p>The global consensus on the threat of climate change risk leads to an agreement to mitigate higher greenhouse gas emissions and limit global mean temperature rise to below 2 ℃ and, ideally, below 1.5 ℃ by 2050. In achieving the mean temperature target, international organisations like the World Bank, Organisation of Economic Co-operation Development and United Nations strongly suggest that policymakers implement a carbon pricing policy. A carbon tax is a market-based policy that has gained attention from many policymakers to reduce carbon emissions and increase the government's revenue. Designing a feasible carbon tax framework is crucial to ensure effectiveness and public acceptability. However, policy design in developing countries may be more complicated than in developed countries due to insufficient income and resources, social inequity, and poverty. This paper discusses the features of a carbon tax and the dimensions of designing an effective carbon tax policy for developing nations. A simplified framework for carbon tax implementation in developing countries is provided. The framework should be a foundation for developing countries to implement and develop a feasible and acceptable carbon tax policy.</p> </abstract>

Carbon tax as the most appropriate carbon pricing mechanism for developing countries and strategies to design an effective policy

<abstract> <p>The global consensus on the threat of climate change risk leads to an agreement to mitigate higher greenhouse gas emissions and limit global mean temperature rise to below 2 ℃ and, ideally, below 1.5 ℃ by 2050. In achieving the mean temperature target, international organisations like the World Bank, Organisation of Economic Co-operation Development and United Nations strongly suggest that policymakers implement a carbon pricing policy. A carbon tax is a market-based policy that has gained attention from many policymakers to reduce carbon emissions and increase the government's revenue. Designing a feasible carbon tax framework is crucial to ensure effectiveness and public acceptability. However, policy design in developing countries may be more complicated than in developed countries due to insufficient income and resources, social inequity, and poverty. This paper discusses the features of a carbon tax and the dimensions of designing an effective carbon tax policy for developing nations. A simplified framework for carbon tax implementation in developing countries is provided. The framework should be a foundation for developing countries to implement and develop a feasible and acceptable carbon tax policy.</p> </abstract>

Net zero electricity systems in global economies by life cycle assessment (LCA) considering ecosystem, health, monetization, and soil CO2 sequestration impacts

Electrification of all sectors needs net zero electricity (NZE) to slash greenhouse gas emissions (GHG), 38% of the global annual energy-related GHG of 34 Gt CO2eq. NZE is to avoid climate catastrophe, predicted at 2.7 °C rise in global mean temperature by 2100 (at 50% probability). There is no consensus approach to the sustainable development of NZE systems. This study has developed a novel, rigorous, holistic life cycle assessment methodology for a sustainable NZE roadmap or pathway. It identifies the leading fifteen countries with the highest gross domestic products with over 90% GHG. It compiles Ecoinvent life cycle inventory for in-country NZE systems and calculates their life cycle impacts using ReCiPe, Impact 2002+, and Environmental Prices methods. The global mean ranking of non-fossil systems is (kg CO2eq/GJ, US$/GJ): hydro-run-of-river (1.49, 0.73), hydro-reservoir (7.77, 0.91), wind:1–3 MW (7.37, 3.9), solar-20MW (13.94, 4.18), solar-50MW (15.29, 4.84), wind:>3 MW (9.55, 9.68), geothermal (19.99, 9.84), and bioenergy (12.09, 36.28). In decreasing order of significance, sustainability determinants are particulate emissions, land use, human toxicity, climate change, acidification, and ionisation radiation. To hit NZE (0.02–0.24 kg CO2eq/kWh), Brazil, the USA, Spain, Germany, France, Canada, Japan, Italy, and the UK need 52–95% decarbonization. Russia, Indonesia, Mexico, and Turkey can achieve 61%, 31%, 6%, and 4% decarbonization to 0.24–0.56 kg CO2eq/kWh, while with 0.52 and 0.65 kg CO2eq/kWh, China's and India's transitioning may slow down by this time. Robust NZE relies on improving health in developing countries, de-fossilized resource-technology diversification, and natural soil organic carbon sequestration, enhancing biodiversity and forestation.

Long-term temperature and sea-level rise stabilization before and beyond 2100: Estimating the additional climate mitigation contribution from China’s recent 2060 carbon neutrality pledge

As the largest emitter in the world, China recently pledged to reach a carbon peak before 2030 and carbon neutrality before 2060, which could accelerate the progress of mitigating negative climate change effects. In this study, we used the Minimum Complexity Earth Simulator and a semi-empirical statistical model to quantify the global mean temperature and sea-level rise (SLR) response under a suite of emission pathways that are constructed to cover various carbon peak and carbon neutrality years in China. The results show that China will require a carbon emission reduction rate of no less than 6%/year and a growth rate of more than 10%/year for carbon capture capacity to achieve carbon neutrality by 2060. Carbon peak years and peak emissions contribute significantly to mitigating climate change in the near term, while carbon neutrality years are more influential in the long term. Mitigation due to recent China’s pledge alone will contribute a 0.16 °C–0.21 °C avoided warming at 2100 and also lessen the cumulative warming above 1.5 °C level. When accompanied by coordinated international efforts to reach global carbon neutrality before 2070, the 2 °C target can be achieved. However, the 1.5 °C target requires additional efforts, such as global scale adoption of negative emission technology for CO2, as well as a deep cut in non-CO2 GHG emissions. Collectively, the efforts of adopting negative emission technolgy and curbing all greenhouse gas emissions will reduce global warming by 0.9 °C −1.2 °C at 2100, and also reduce SLR by 49–59 cm in 2200, compared to a baseline mitigation pathway already aiming at 2 °C. Our findings suggest that while China’s ambitious carbon-neutral pledge contributes to Paris Agreement’s targets, additional major efforts will be needed, such as reaching an earlier and lower CO2 emission peak, developing negative emission technology for CO2, and cutting other non-CO2 GHGs such as N2O, CH4, O3, and HFCs.

Energy system transformations and carbon emission mitigation for China to achieve global 2 °C climate target

The Paris Agreement calls for countries to pursue efforts to limit global-mean temperature rise to 2 °C compared to the pre-industrial level. To achieve this, it is essential to accelerate the low-carbon transition of energy system. China is the largest carbon emitter and plays a decisive role in mitigating global climate change. The transition pathways for China to contribute to meeting the global 2 °C target, however, have not been extensively explored. Here we develop a bottom-up national energy technology model (C3IAM/NET), a linear optimization model, to reveal the energy consumption, carbon emissions and technology pathway at the national and sectoral levels in line with the 2 °C climate target. Results show that China's carbon emissions need to peak at the year 2023 and reduce to 3.56 GtCO2 by mid-century. During the 2020–2050 planning horizon, the remaining carbon budget is estimated to be controlled within 234 GtCO2, with a cumulative emission reduction of 165.3 GtCO2, of which the power sector bearing the largest share of responsibility, followed by the industry, transportation and building sectors. We project that China's primary energy consumption needs to peak before 2040 and the proportion of non-fossil energy in energy structure needs to reach 76% by 2050, and about 88.4% of electricity production comes from renewables and nuclear energy.

Heat Waves Alter Macrophyte-Derived Detrital Nutrients Release under Future Climate Warming Scenarios.

In addition to a rise in global air and water mean temperatures, extreme climate events such as heat waves are increasing in frequency, intensity, and duration in many regions of the globe. Developing a mechanistic understanding of the impacts of heat waves on key ecosystem processes and how they differ from just an increase in mean temperatures is therefore of utmost importance for adaptive management against effects of global change. However, little is known about the impact of extreme events on freshwater ecosystem processes, particularly the decomposition of macrophyte detritus. We performed a mesocosm experiment to evaluate the impact of warming and heat waves on macrophyte detrital decomposition, applied as a fixed increment (+4 °C) above ambient and a fluctuating treatment with similar energy input, ranging from 0 to 6 °C above ambient (i.e., simulating heat waves). We showed that both warming and heat waves significantly accelerate dry mass loss of the detritus and carbon (C) release but found no significant differences between the two heated treatments on the effects on detritus dry mass loss and C release amount. This suggests that moderate warming indirectly enhanced macrophyte detritus dry mass loss and C release mainly by the amount of energy input rather than by the way in which warming was provided (i.e., by a fixed increment or in heat waves). However, we found significantly different amounts of nitrogen (N) and phosphorus (P) released between the two warming treatments, and there was an asymmetric response of N and P release patterns to the two warming treatments, possibly due to species-specific responses of decomposers to short-term temperature fluctuations and litter quality. Our results conclude that future climate scenarios can significantly accelerate organic matter decomposition and C, N, and P release from decaying macrophytes, and more importantly, there are asymmetric alterations in macrophyte-derived detrital N and P release dynamic. Therefore, future climate change scenarios could lead to alterations in N/P ratios in the water column via macrophyte decomposition processes and ultimately affect the structure and function of aquatic ecosystems, especially in the plankton community.

A process‐based soil erosion model ensemble to assess model uncertainty in climate‐change impact assessments

AbstractThe impact of climate change on future soil loss is commonly assessed with soil erosion models, which are suggested to be an important source of uncertainty. Here, we present a novel soil erosion model ensemble to assess model uncertainty in climate‐change impact assessments. The model ensemble consists of five continuous process‐based soil erosion models that run at a daily time step (i.e., DHSVM, HSPF, INCA, MMF, SHETRAN). The models were implemented in the SPHY hydrological model and simulate detachment by raindrop impact, detachment by runoff, and immediate deposition. The soil erosion model ensemble was applied in a semiarid catchment in the southeast of Spain. We applied three future climate scenarios based on global mean temperature rise (+1.5, +2 and +3°C). Data from two contrasting regional climate models were used to assess how an increase and a decrease in projected extreme precipitation affect model uncertainty. Soil loss is projected to increase (up to 95%) and decrease (up to −30%) under climate change, mostly reflecting the change in extreme precipitation. Model uncertainty is found to increase with increasing slope, extreme precipitation and runoff, which reveals some inherent differences in model assumptions among the five models. Moreover, the model uncertainty increases in all climate change scenarios, independent of the projected change in annual precipitation and extreme precipitation. This stresses the importance to consider model uncertainty through model ensembles of climate, hydrology, and soil erosion in climate‐change impact assessments.

Global analysis of sea level rise risk to airports

Major airports are already at risk of coastal flooding. Sea level rise associated with a global mean temperature rise of 2 °C would place 100 airports below mean sea level, whilst 1238 airports are in the Low Elevation Coastal Zone. A global analysis has assessed the risk to airports in terms of expected annual disruption to routes. The method integrates globally available data of airport location, flight routes, extreme water levels, standards of flood protection and scenarios of sea level rise. Globally, the risk of disruption could increase by a factor of 17–69 by 2100, depending on the rate of sea level rise. A large number of airports are at risk in Europe, Norther American and Oceania, but risks are highest in Southeast and East Asia. These coastal airports are disproportionately important to the global airline network, by 2100 between 10 and 20% of all routes are at risk of disruption. Sea level rise therefore poses a systemic risk to global passenger and freight movements. Airports already benefit from substantial flood protection that reduces present risk by a factor of 23. To maintain risk in 2100 at current levels could cost up to $57BN. Although the cost of protecting larger airports is higher, busier airports are typically well protected and more likely to have better access to adaptation finance. However, 995 coastal airports operate 5 commercial routes or fewer. More detailed consideration of these airports shows that regions, especially low lying islands, will experience disproportionate impacts because airports can provide important economic, social, and medical lifelines. Route disruption was used as the risk metric due to its global coverage and relationship with direct economic impacts. Further work should collate a wider range of impact metrics that reflect the criticality of an airport in terms of the isolation and socio-economic context of the location it serves.

Increase in Population Exposure Due to Dry and Wet Extremes in India Under a Warming Climate

AbstractDry and wet extremes affect agricultural production, infrastructure, and socioeconomic well‐being of about 1.4 billion people in India. Despite the profound implications of dry and wet extremes, their changes in the observed and projected climate in India are not well quantified. Here, using the observations from multiple sources, we show that the area affected by dry extremes during the monsoon season (June–September) and water‐year (June–May) has significantly increased (~1% per decade; p value < 0.05) over the last six decades (1951–2015) in India. On the other hand, the area affected by wet extremes does not exhibit any significant trend over the same time period. Dry and wet extremes in the monsoon season are corroborated with the positive phase and negative phase of the sea surface temperature (SST) anomalies in the tropical Pacific Ocean (Niño 3.4 region). Global climate models (GCMs) project an increase of more than 25–30% (±3–6%) in the combined area affected by the dry and wet extremes in India by the end of the 21st century. The frequency of both dry and wet extreme years is also projected to increase in the majority of India (>80%) under a warmer world if the global mean temperature rises above 1.5°C (or 2°C) from a preindustrial level. Moreover, the population exposed to the dry and wet extremes is likely to increase threefold under the projected 2°C warmer world. Therefore, limiting global mean temperature rise below 2°C can substantially reduce the area and population exposure due to dry and wet extremes in India.

Large Chinese land carbon sink estimated from atmospheric carbon dioxide data.

Limiting the rise in global mean temperatures relies on reducing carbon dioxide (CO2) emissions and on the removal of CO2 by land carbon sinks. China is currently the single largest emitter of CO2, responsible for approximately 27 per cent (2.67petagrams of carbon per year) of global fossil fuel emissions in 20171. Understanding of Chinese land biosphere fluxes has been hampered by sparse data coverage2-4, which has resulted in a wide range of a posteriori estimates of flux. Here we present recently available data on the atmospheric mole fraction of CO2, measured from six sites across China during 2009 to 2016. Using these data, we estimate a mean Chinese land biosphere sink of -1.11±0.38petagrams of carbon per year during 2010 to 2016, equivalent to about 45 per cent of our estimate of annual Chinese anthropogenic emissions over that period. Our estimate reflects a previously underestimated land carbon sink over southwest China (Yunnan, Guizhou and Guangxi provinces) throughout the year, and over northeast China (especially Heilongjiang and Jilin provinces) during summer months. These provinces have established a pattern of rapid afforestation of progressively larger regions5,6, with provincial forest areas increasing by between 0.04 million and 0.44 million hectares per year over the past 10 to 15years. These large-scale changes reflect the expansion of fast-growing plantation forests that contribute to timber exports and the domestic production of paper7. Space-borne observations of vegetation greenness show a large increase with time over this study period, supporting the timing and increase in the land carbon sink over these afforestation regions.