Climate change-driven dual heatwave-driven drought-wet extremes (DHDWEs)—characterized by abrupt drought-flood transitions under heatwaves—pose growing threats to urban sustainability. Analyzing 334 Chinese cities (1980–2023), we identified newly rising DHDWE frequency (0.34 ± 0.09 events yr−1) and intensity (0.08 ± 0.04 units yr−1), with distinct north-south spatial divergence. We introduced a novel “time tightness” metric to indicate the relative time available for recovery or response between the two extreme phases of a DHDWE, revealing a dangerous downward trend. Panel model analysis shows that DHDWEs cause nonlinear economic losses, with a potential early-warning threshold emerging when time tightness falls below 0.33. Projections under SSP585 suggest DHDWE frequency will surge by 270 ± 120% by 2100, further compressing recovery windows. We therefore propose a Threshold-Alert, Window-Action framework that uses empirical timing thresholds to guide risk prioritization and earlier preparedness, supporting proactive adaptation for cities facing compressed recovery windows and rising economic risk.

China has been vigorously developing the solar photovoltaic (PV) industry to address climate change and air pollution. While aerosols constitute a significant air pollutant that impairs PV generation efficiency, few studies have examined how China’s clean air action (CAA) plan has influenced solar PV performance. To address this gap, we employ the PVLIB-Python model to quantify PV capacity factors and power generation changes across China, due to the CAA plan in China from 2013 to 2020. We find that improved air quality has substantially enhanced PV generation, particularly in eastern China, generating up to 41.3 TWh additional electricity per year, estimated with current PV capacity. The largest increases are in provinces such as Shandong and Henan, with heavier air pollution and higher PV installation. By employing multiple CMIP6 models, we also estimate potential future PV power generation changes in China. We find that with sustainable development and strong climate change mitigation policies, the reduced air pollution and increased solar radiation can potentially increase the PV power generation by 37.4–52.6 TWh per year by the 2050s, without even considering the newly installed PV facilities.

Achieving carbon neutrality and improving air quality are pivotal sustainability strategies for the Global South countries. However, their global climate impacts over a realistic timescale remain unclear. Here we evaluate the climate impacts of China's carbon neutrality and Beautiful China policies using a fully coupled Earth system model and updated future anthropogenic emission scenarios. We find that, for an unexpectedly long time through ~2070, China's air pollutant reductions can cause a large global surface warming (0.12 ± 0.09 K for 2050-2070) that almost offsets the cooling from concurrent CO2 emission reduction (0.16 ± 0.05 K for 2050-2070), compared to a business-as-usual scenario. This warming is mainly attributed to reduced SO2 and organic matter emissions. Moreover, combined air pollutants and CO2 declines create a striking hemispheric temperature change contrast, because of the stronger aerosol-induced heating in the Northern Hemisphere. Considering that most future air pollutant reductions represent synergistic effects of carbon neutrality policies, the associated inevitable warming effect over decades highlights the importance of exploring more aggressive policies including early carbon neutrality, methane reductions, and negative carbon emissions.

Methane is a powerful greenhouse gas with a shorter lifetime than carbon dioxide (CO2), making it an important target for near-term climate action. The Global Methane Pledge (GMP) aims to cut anthropogenic methane emissions by 30% from 2020 levels by 2030. Using an Earth system model with interactive CH4 sources and sinks, we assess the Pledge's impact through 2050. Results show that current GMP commitments deliver only a 10% cut by 2030-well below the target. Only the maximum technically feasible reduction (MTFR) pathway can achieve the 30% goal. By 2050, current GMP commitments lowers methane concentrations by 3% relative to 2025, while MTFR achieves 8%. Both pathways slow warming slightly, avoiding about 0.1 degrees C of global temperature rise, with the Arctic seeing the greatest benefits (up to 2 degrees C less warming). Without wider participation, the GMP with current signatories will fall short of its targets and Paris Agreement goals.

Observational evidence reveals a pronounced wetting trend over Central Asia in recent decades, with the most substantial increases occurring during winter and summer. Yet the extent to which the drivers of these changes differ seasonally remains unknown. Here, we use single-forcing experiments from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP) to examine the effects of various external forcings on winter and summer precipitation across Central Asia and to explore the physical mechanisms underlying seasonal precipitation changes. We find that greenhouse gas (GHG) forcing mainly increases winter precipitation by enhancing atmospheric moisture content through warming. In contrast, in summer, Asian sulfate aerosols enhance precipitation by modulating the westerly jet, which strengthens atmospheric moisture transport into the region. Asian black carbon exerts an opposing influence that partially offsets the sulfate-induced effect. Further attribution analysis based on CMIP6 simulations reinforces these sensitivity results and shows that GHG forcing is the primary driver of winter precipitation increases whereas anthropogenic aerosols dominate summer trends. Future CMIP6 projections suggest that under moderate- to high-emission scenarios, winter precipitation will continue to rise due to increasing GHG concentrations, while summer precipitation may decline across much of Central Asia as a result of reduced aerosol emissions following Asian clean air policies. These findings highlight a distinct seasonality in the drivers of recent precipitation increase and suggest a plausible divergence in future winter and summer precipitation trends.

Abstract Improved management of nitrogen could provide environmental benefits. Crop yields can be affected by reactive nitrogen emissions (NH 3 , NO X , and N 2 O) as they influence climate, ozone formation, and nitrogen deposition thus crop fertilization. Here we constructed a integrated framework to evaluate the benefits of improving agricultural nitrogen management for reducing reactive nitrogen emissions and their consequent impacts on crop yields through above‐mentioned pathways, with impacts monetized addressing dynamic food prices. Considering three levels of increasingly stringent nitrogen management scenarios from 2020 to 2050, we find that anthropogenic emissions of NH 3 , NO X , and N 2 O could be reduced by 44.5%, 61.1%, and 35.2%, respectively, by 2050 relative to 2020. With the most effective nitrogen management strategies, crop yields during 2040–2050 are projected to increase by up to 22.5%, 13.1%, 22.9%, and 16.6% for maize, rice, soybeans, and wheat, respectively, corresponding to average economic gains of 10.2, 11.8, 11.8, and 7.4 billion dollars. These results indicate that enhanced nitrogen management can substantially increase crop production, providing a strong rationale for integrating nitrogen emission limits into policy frameworks.

In recent years, the Earth has likely experienced an accelerated warming trend, raising growing interest in the possible contributing factors. From 2013 to 2023, global anthropogenic air pollutant emissions declined significantly and brought enormous public health benefits, but the contribution of reduced aerosol masking of greenhouse warming to recent trends remains uncertain. Using two state-of-the-art global climate models, we show that global air pollutant emission reductions during 2013-2023 caused a global effective radiative forcing of 0.16 W/m2 (90% CI: 0.13 to 0.20), with international shipping, China, and other land regions contributing 0.05 W/m2 (0.00 to 0.09), 0.07 W/m2 (0.03 to 0.11), and 0.05 W/m2 (0.00 to 0.09), respectively. International shipping contributes disproportionately to radiative forcing relative to its emission reductions, highlighting its high forcing efficiency. The combined forcings are estimated to have contributed a warming of 0.044 °C (0.012 to 0.076) over 2013-2023, accounting for 52% (14 to 90%) of the observed warming acceleration (0.084 °C/decade) relative to the 1970-2012 trend. Especially strong reductions in aerosol-cloud interactions are found over the North Pacific, driven primarily by the downwind impacts of East Asian emission reductions. Aerosol unmasking contributes to the recent acceleration of warming and highlights the importance of accurately quantifying air pollutant emission changes for future climate projections.

Climate change alters the frequency and intensity of wildfires, but its impact on the seasonal patterns of wildfires remains underexplored. Here, we quantify historical changes in wildfire seasonality across different ecoregions in North America and assess how climate change may affect these seasonal patterns. Our study finds that boreal and taiga forests have experienced a clear advance in seasonal wildfire activity, whereas Mediterranean and desert regions show delayed and extended late-season burning. Prairie and humid forest regions exhibit comparatively muted change. Attribution analysis shows that atmospheric dryness is the dominant control, while antecedent temperature, precipitation, and soil moisture indirectly shape wildfire risk through vegetation and fuel continuity at different lag times. These findings provide a basis for interpreting future region-specific changes in wildfire seasonality and emphasize the need for region-specific assessments of future wildfire activity. Plain Language Summary Wildfire seasons across North America are shifting in different ways as the climate changes. We combined satellite records, climate projections, and statistical models to examine how wildfire seasons have changed and how they may shift under future warming. Our analysis shows that wildfire seasons are moving earlier in northern forests, barely changing in grasslands, and shifting later in drought-prone western regions. These differences occur because each region responds differently to warming, drying, and changes in vegetation. Our findings highlight that wildfire risk will evolve in distinct ways across ecosystems, underscoring the need for region-specific planning and adaptation.

Climate change and ozone change are two major channels through which climate policies influence agricultural production, yet most studies assess climate or ozone in isolation, which can limit the accuracy of estimated climate policy effects. Here we use an integrated model to quantify how carbon neutrality policies pledged by 153 countries affect yields of maize, rice, soybean and wheat and the associated economic outcomes. We show that excluding ozone change may understate the benefits of existing carbon neutrality policies for the four main crops, by up to 38.7%. By including the combined effect of ozone and climate, carbon neutrality policies can prevent 0.5-41.5% in losses, and more than 70% of the crop area would experience crop gains compared with the no policy scenario. For countries that still experience agricultural losses, we discuss options to reduce food security risks in terms of mitigation policies, adaptation measures and agricultural trade agreements.

Reactive nitrogen (Nr) management links climate policy, air quality and food production, yet its combined impacts remain poorly quantified. Here, we conduct ensemble simulations with two global climate models, Goddard Institute for Space Studies (GISS) and Community Earth System Model (CESM), to evaluate the air quality and climate co-benefits of Nr mitigation. By mid-century, both models simulate positive aerosol radiative forcing (RF) and negative ozone RF, yielding a net positive RF of 150 mW m−2 (95% CI: 120–180 mW m−2) in GISS and 60 mW m−2 (10–120 mW m−2) in CESM. Global air quality also improves, with global area-weighted mean PM2.5 concentrations decreasing by 0.16 µg m−3 (0.07–0.25 µg m−3) and 0.13 µg m−3 (0.05 to 0.21 µg m−3) and global area-weighted mean maximum daily 8-h average ozone decreasing by 1.69 ppb (1.48–1.89 ppb) and 0.99 ppb (0.88–1.10 ppb) in GISS and CESM, respectively. Regional PM2.5 reductions exceed 5 µg m−3. Moreover, more than 80% of avoided premature deaths occur across 0–60°N. Although efficient nitrogen management induces a modest, transient near-term climate penalty, long-term climate benefits from lower N2O emissions eventually offset this effect and deliver major air quality, health, and ecosystem co-benefits.

Global air pollution policies have drastically lowered anthropogenic emissions, yet climate change threatens regional air quality through poorly understood natural feedbacks. Extreme heat accelerates biogenic volatile organic compound and soil nitrogen emissions, fueling ozone and secondary organic aerosol formation. Although standalone impacts of these biogenic sources are documented, chemical interactions between co-elevated vegetation and soil fluxes remain unconstrained. Here we show that a temperature-driven synergistic mechanism between biogenic terpenoids and soil nitrogen emissions severely exacerbated secondary air pollution during China's unprecedented 2022 heatwave. Integrating ground observations, satellite data, and chemical transport modeling, we demonstrate that a massive surge in biogenic terpenoids enhances atmospheric oxidation capacity by generating reactive peroxy radicals. These radicals accelerate the conversion of soil nitric oxide to nitrogen dioxide without consuming ozone, driving a 21% regional ozone increase across the Yangtze River Basin and boosting secondary organic aerosol loads by up to 4 μg m−3. These findings reveal a potent natural feedback loop that counteracts anthropogenic mitigation gains, underscoring the necessity of integrating coupled ecological dynamics into future climate adaptation and pollution control strategies.

Abstract. Many halocarbons are powerful greenhouse gases and also influence climate indirectly through depletion of stratospheric ozone which opposes their direct greenhouse effect. Changes in effective radiative forcing (ERF) from historical ozone depletion have been diagnosed from model experiments with perturbed halocarbons run under the sixth Coupled Model Intercomparison Project. This is more negative than the offline stratospheric-temperature-adjusted radiative forcing (SARF). Including effects of ozone depletion on the methane lifetime makes the historical net ERF of ozone depleting substances consistent with zero. The Integrated Ozone Depletion (IOD) metric has been used to apportion this ERF between the halocarbon species and thereby derive indirect 100-year Global Warming Potentials (GWP100s) for a suite of halocarbons. The indirect GWP100 for CFC-11 is enough to make the net GWP100 likely negative, whereas the indirect contribution for CFC-12 is smaller due to a combination of longer stratospheric lifetime and fewer chlorine atoms. use of the online ERF, rather than the offline SARF, allows the model physics to account for changes in stratospheric temperature (as well as tropospheric temperature, water vapour and clouds) rather than estimating stratosphere temperature changes using fixed dynamical heating. This online calculation of radiative forcing rather than offline leads to approximately double the indirect GWPs compared to World Meteorological Organization assessments. This formalism can be used with other estimates of ozone ERF, as the indirect GWPs scale linearly with this quantity.

Escalating wildfire frequency increases population exposure to wildfire smoke. To evaluate the association between wildfire-specific particulate matter (PM2.5) and acute health impacts a retrospective cohort study was conducted utilizing National COVID Cohort Collaborative health records from 109,012 patients across 58 US health systems from 2020 to 2021. County-level wildfire-specific PM2.5 concentrations were estimated using a fire emissions database and chemical transport modeling. Generalized linear mixed-effects models were used to analyze the association between weekly county-level wildfire-specific PM2.5 exposure (up to 50 μg/m3) and hospital encounters for a series of cardiac, pulmonary, obstetric and neonatal outcomes. Statistically significant increases in weekly encounters per county of residence were observed for every 10 μg/m3 rise in weekly maximum wildfire-specific PM2.5 for acute myocardial infarction (0.084, 95% CI, 0.023-0.146), cardiac arrest (0.011, 95% CI, 0.001-0.021), heart failure (0.083, 95% CI, 0.024-0.142), atrial fibrillation (0.115, 95% CI, 0.014-0.216), COPD exacerbation (0.034, 95% CI, 0.001-0.066) and pulmonary embolism (0.048, 95% CI, 0.003-0.094). COVID infection status was not found to have a modifying effect on these relationships. There was no significant increase in COVID pneumonia admissions in response to increasing wildfire smoke. These findings demonstrate quantifiable increases in acute cardiorespiratory morbidity associated with wildfire smoke exposure.

Surface ozone concentrations typically increase with temperature, but emerging evidence indicates a decline at extreme-high temperatures. This reversal challenges the prevailing expectation of monotonic ozone increase under global warming and highlights a narrow temperature range in which peak ozone is most likely to occur, which is crucial for predicting extreme pollution events. Despite its importance, the global extent and underlying mechanism of this ozone-temperature reversal remain unclear. Using thousands of monitoring sites across the Northern Hemisphere, we demonstrate that this reversal is widespread and robust. Once temperatures exceed a threshold peak-ozone temperature, enhanced buoyancy-driven convection clears ozone and its precursors, thereby decreasing surface ozone. We show that this peak-ozone temperature corresponds closely to the theoretically derived onset of thermally driven convection and is governed by atmospheric thermodynamic conditions. Climate projections indicate that the peak-ozone temperature will rise due to enhanced convection inhibition under global warming. This upward shift delays the onset of ozone reversal, resulting in higher peak ozone levels and longer periods of elevated ozone exposure during heatwaves. Future mitigation efforts must anticipate the growing risk of co-occurrence of ozone pollution and heat extremes as surface ozone will peak both at higher temperatures and with higher values.

Methane is a potent greenhouse gas which has substantially contributed to climate change since the pre-industrial era, second only in importance to carbon dioxide. Due to its short atmospheric lifetime and high global warming potential, methane emissions have disproportionately large impacts on near-term climate change. Beyond its direct role as a greenhouse gas, methane also has other important implications for climate, human health, air quality and vegetation, largely due to its impact on tropospheric ozone. Thus, reducing methane emissions has been identified as a key policy lever for delaying the worst impacts of near-term climate change with expected co-benefits for health and air quality. The most notable of these efforts is the Global Methane Pledge which aims to achieve a 30% reduction in global anthropogenic methane emissions by 2030 as compared to 2020. And yet, in many respects, methane mitigation has been overlooked relative to other climate mitigation strategies. Existing modelling evidence for the estimating the potential climate benefits of methane mitigation rely extensively on idealised climate emulators or comprehensive modelling studies based on a limited number of models and ensemble members. Both approaches have important limitations. Hence, there is a pressing need for a co-ordinated intermodel comparison project which uses state-of-the-art ESMs in which all modelling groups prescribe identical reductions in methane concentrations or emissions, all modelling groups use the same baseline scenario, and sufficient ensemble members are simulated to investigate the broader climate and health impacts of methane mitigation. MethaneMIP has been envisioned to undertake these tasks.In this talk I will introduce the MethaneMIP protocol and the two new methane reduction scenarios ‘Technical Measures’ and ‘Ambitious’, which are both branched from SSP2-4.5 and cover the period 2020-2050. The overarching aim of MethaneMIP is to provide a policy-relevant state-of-the-art estimate of the climate and health impacts of methane mitigation, and a robust quantification of the uncertainties, as well as furthering our understanding of methane’s role in the climate system. Over ten modelling centres from across the world are participating in MethaneMIP, with simulations for the core MethaneMIP experiments currently underway. For the first time, I will present the preliminary results of MethaneMIP as pertaining to the research questions it was set up to address, including: What are the best estimates of the expected climate and health benefits of plausible methane mitigation by mid-century? Which near-term climate events projected to occur may be delayed or avoided by curbing methane emissions? What are potential impacts of successful implementation of the Global Methane Pledge? When should we expect the climate or health signal from reduced methane to be detectable in the presence of internal variability? I will finish by discussing the implications of MethaneMIP for climate policy, as well as introducing the flagship emissions-driven MethaneMIP simulations which will be performed later this year.

We have used the NASA Goddard Institute for Space Studies (GISS) Earth system model GISS-E2.1 to study the future budgets and trends of global and regional CH _4 under different emission scenarios, using both the prescribed GHG concentrations as well as the interactive CH _4 sources and sinks setup of the model, to quantify the model performance and its sensitivity to CH _4 sources and sinks. We have used the Current Legislation (CLE) and the maximum feasible reduction (MFR) emission scenarios from the ECLIPSE V6b emission database to simulate the future evolution of CH _4 sources, sinks, and levels from 2015 to 2050. Results show that the prescribed GHG version underestimates the observed surface CH _4 concentrations during the period between 1995 and 2023 by 1%, with the largest underestimations over the continental emission regions, while the interactive simulation underestimates the observations by 2%, with the biases largest over oceans and smaller over the continents. For the future, the MFR scenario simulates lower global surface CH _4 concentrations and burdens compared to the CLE scenario, however in both cases, global surface CH _4 and burden continue to increase through 2050 compared to present day. In addition, the interactive simulation calculates slightly larger O _3 and OH mixing ratios, in particular over the northern hemisphere, leading to slightly decreased CH _4 lifetime in the present day. The CH _4 forcing is projected to increase in both scenarios, in particular in the CLE scenario, from 0.53 W m ^−2 in the present day to 0.73 W m ^−2 in 2050. In addition, the interactive simulations estimate slightly higher tropospheric O _3 forcing compared to prescribed simulations, due to slightly higher O _3 mixing ratios simulated by the interactive models. While in the CLE, tropospheric O _3 forcing continues to increase, the MFR scenario leads to a decrease in tropospheric O _3 forcing, leading to a climate benefit. Our results highlight that in the interactive models, the response of concentrations are not necessarily linear with the changes in emissions as the chemistry is non-linear, and dependent on the oxidative capacity of the atmosphere. Therefore, it is important to have the CH _4 sources and chemical sinks to be represented comprehensively in climate models.

Anthropogenic emissions of black carbon (BC) aerosols are generally thought to warm the climate. However, the magnitude of this warming remains highly uncertain due to limited knowledge of BC sources; optical properties; and atmospheric processes such as transport, removal, and cloud interactions. Here, we assess and constrain estimates of the historical warming influence of BC using recent observations and emission inventories. Based on simulations from four climate models, we show that the current global mean surface temperature change from anthropogenic BC due to aerosol-radiation interaction spans a factor of three- from +0.02 +/- 0.02 K to +0.06 +/- 0.05 K. Rapid atmospheric adjustments reduce the instantaneous radiative forcing by nearly 50% (multi-model mean), substantially lowering the net warming. Yet, recent satellite constraints suggest a stronger effect, highlighting the need for a more comprehensive reassessment of BC's climate influence.