Exposure to ambient air pollution, including ozone and fine particulate matter (PM2.5), is the world's leading environmental health risk factor. Estimating how this burden may change in the future depends on projecting population growth and age structure as well as understanding how future meteorological changes may impact the production and removal of pollutants from the atmosphere. The net impact of these factors on a global scale has not been well-characterized. Here, we leverage recent meteorology, exposure, and mortality output from general circulation, atmospheric chemistry, and health impact models to isolate how changes in meteorology and populations will impact future global air-pollution-related mortality and the associated monetized impacts by the degree of global temperature change. In contrast to previous studies, we estimate that changes in meteorologically driven air pollution, in the absence of pollutant precursor emission changes, will result in 180 000 fewer deaths annually by 2100 relative to current levels, an annual monetized benefit of $7.3 trillion. Reductions are driven by decreases in PM2.5-attributable mortality in populated regions but are substantially offset by global increases in ozone-related mortality. We also highlight striking regional differences in the sign of net pollutant impacts by 2100, with net pollution decreases in the Northern Hemisphere driven by reductions in nitrate aerosol, while increases in both ozone and organic aerosol at higher temperatures lead to net increases in pollutant impacts in the Southern Hemisphere. Lastly, we assess sensitivities of these results to meteorological projections, health impact functions, and 10 000 future warming scenarios.

BACKGROUND:Links between climate change and mental health concerns in the USA are recognised, but research is underdeveloped. Many studies rely on self-reported exposures, non-representative samples, or inconsistent definitions of mental health outcomes, limiting their utility in supporting robust, population-scale projections to inform the public. Few studies have attempted to quantify future impacts, and those that do have largely focused on suicide rather than broader mental health morbidity. To address this gap, we projected the impact of 1-6°C contiguous US warming and the associated precipitation changes on self-reported mental health difficulties, anxiety, and depression symptom-days among adults relative to 2005 baseline climate and 2015 baseline health data. METHODS:We combined epidemiologically derived exposure-response relationships with projections from five CMIP6 climate models to estimate mental health impacts (mental health difficulties, anxiety, and depression symptom-days) in adults under present-day (2022) and end-of-century (2095) sociodemographic scenarios. We used data from the US Centers for Disease Control & Prevention Behavioral Risk Factor Surveillance System (BRFSS) to inform baseline symptom-day incidence rates (2013-23 datasets) and to estimate sex-specific and age group-specific mental health difficulty day allocation ratios for anxiety and depression (2018 Depression and Anxiety Module for Oregon and Tennessee). Analyses covered acute (short-term, over the past month) temperature and precipitation exposures by sex and income, and both acute and chronic (multi-year average maximum temperature) exposures for urban populations. Baseline symptom-day incidence rates were estimated using negative binomial regression analysis of BRFSS 2013-23 data, stratified by month, state, sex, and age group. Economic valuation was based on an original analysis of the Medical Expenditure Panel Survey 2018-21 data to develop fixed-effects regression-based estimates of health-related quality of life losses from anxiety and depression symptom-days. These daily losses are monetised using a scaled value per quality-adjusted life-year, calculated by dividing the United States Environmental Protection Agency Value of a Statistical Life by quality-adjusted life expectancy. We used Monte Carlo simulations to propagate uncertainty across health, climate, and valuation inputs. FINDINGS:Assuming present-day sociodemographics, warming of 1-6°C would result in 401 million to 1·8 billion and 329 million to 1·4 billion excess annual self-reported anxiety and depression symptom-days in adults, respectively, representing a 5-23% increase from baseline. Corresponding annual values of excess anxiety and depression burden are US$13 billion to $57 billion and $11 billion to $47 billion, respectively (2023 US dollars, undiscounted). We estimate an additional two to seven anxiety and one to six depression symptom-days per person-year, with larger burdens-four to 15 and three to 14 symptom-days, respectively-among low-income subpopulations. The greatest impacts are projected to occur in Appalachia. Using 2095 sociodemographics resulted in an increase in symptom days of almost 30% and an increase in monetised impacts of almost 90%. INTERPRETATION:These findings underscore the need for mental health investment in regions with restricted adaptive capacity due to economic hardship. Promoting individual and community resilience is crucial. FUNDING:US Environmental Protection Agency.

Exposure to ambient air pollution, including ozone and fine particulate matter (PM2.5), is the world's leading environmental health risk factor. Estimating how this burden may change in the future depends on projecting population growth and age structure as well as understanding how future meteorological changes may impact the production and removal of pollutants from the atmosphere. The net impact of these factors on a global scale has not been well-characterized. Here, we leverage recent meteorology, exposure, and mortality output from general circulation, atmospheric chemistry, and health impact models to isolate how changes in meteorology and populations will impact future global air-pollution-related mortality and the associated monetized impacts by the degree of global temperature change. In contrast to previous studies, we estimate that changes in meteorologically driven air pollution, in the absence of pollutant precursor emission changes, will result in 180 000 fewer deaths annually by 2100 relative to current levels, an annual monetized benefit of $7.3 trillion. Reductions are driven by decreases in PM2.5-attributable mortality in populated regions but are substantially offset by global increases in ozone-related mortality. We also highlight striking regional differences in the sign of net pollutant impacts by 2100, with net pollution decreases in the Northern Hemisphere driven by reductions in nitrate aerosol, while increases in both ozone and organic aerosol at higher temperatures lead to net increases in pollutant impacts in the Southern Hemisphere. Lastly, we assess sensitivities of these results to meteorological projections, health impact functions, and 10 000 future warming scenarios.

This research investigates the projected risks of future climate trends on tropical cyclone-induced power outages in the Gulf and Atlantic coast of the United States, focusing on the disproportionate impacts on vulnerable populations and the economic burdens associated with such events. Our methodology integrates four well-documented models to estimate changes in power outage rates, sociodemographic inequities, and economic costs due to tropical cyclone projections. Synthetic tropical cyclones were generated using data from seven global climate models (GCMs), used to compare power outage risks at the census tract level along two periods: hindcast (1995-2014) and late-century (2071-2100) using the SSP5-8.5 scenario. The late-century results from each model were scaled to align with a global warming scenario of 3 °C. We evaluated the uncertainty of these projections by considering the agreement among the GCMs outage projections. Results highlight a significant increase in power outage risks and high agreement in northern Florida, Georgia, the mid-Atlantic, and the North Atlantic coast. Distributional impact analyses indicate higher outage risks for Hispanic, non-White, and low-income populations, while economic projections show annual costs rising from $6.2 billion in the hindcast to over $11 billion for the 3 °C scenario. The findings highlight the need for adaptive strategies and equitable resource allocation to mitigate these growing risks due to future climate projections.

BACKGROUND:Studies have documented the effect of increased nuisance high-tide flooding on traffic disruption and delays as well as infrastructure maintenance and repair costs. Recent research suggests that high-tide flooding is also associated with more extreme outcomes, including increased mortality risk among adults aged 65 years and older. The aim of this study was to leverage these new findings to project future premature deaths and associated economic costs among older adults in coastal areas of the USA throughout the 21st century under various climate change scenarios. METHODS:We estimated the relationship between global sea level rise and high-tide flooding. We then employed five projections of relative mean sea level from the Fifth National Climate Assessment to develop a probabilistic distribution of high-tide flooding scenarios. Combining population and baseline mortality projections with published estimates of the association between high-tide flooding and premature mortality among adults aged 65 years and older in Florida, USA, we generated a distribution of predicted high-tide flooding mortality impacts across coastal areas of the USA. Because this analysis assumes no change in adaptation strategies, we also presented a stylised scenario that assumes additional action is taken to limit mortality risk. FINDINGS:Our main specification (without additional adaptation) anticipates approximately 230 additional deaths of older adults per year in 2020 relative to 2005, corresponding to monetised damages of US$3·1 billion. By 2100, the model projects nearly 10 000 additional deaths in this age group per year under the same scenario, a 43-fold increase relative to modelled 2005 levels. With some protective measures, the model predicts 5700 additional premature deaths, representing a 57% reduction relative to the main results. INTERPRETATION:The cost of premature mortality in older adults is greater in magnitude than other modelled effects of climate-induced high-tide flooding (eg, value of lost time due to traffic delays). Results suggest further action is needed to (1) identify and protect components of road networks critical for emergency access, (2) build additional, more accessible critical care delivery facilities, and (3) manage the retreat of vulnerable populations to areas with better access to critical care facilities. FUNDING:US Environmental Protection Agency.

Lyme disease (LD) is the most common vector-borne disease in the United States (U.S.). This paper assesses how climate change may influence LD incidence in the eastern and upper Midwestern U.S. and the associated economic burden. We estimated future Ixodes scapularis habitat suitability and LD incidence with a by-degree approach using variables from an ensemble of multiple climate models. We then applied estimates for present-day and projected habitat suitability for I. scapularis, present-day presence of Borrelia burgdorferi, and projected climatological variables to model reported LD incidence at the county level among adults, children, and the total population. Finally, we applied an estimate of healthcare expenses to project economic impacts. We show an overall increase in LD cases with regional variation. We estimate an increase in incidence in New England and the upper Midwestern U.S. and a concurrent decrease in incidence in Virginia and North Carolina. At 3°C of national warming from the 1986–2015 baseline climate, we project approximately 55,000 LD cases, a 38-percent increase from present-day estimates. At 6°C of warming, our most extreme scenario, we project approximately 92,000 LD cases in the region, an increase of 145 percent relative to current levels. Annual LD-related healthcare expenses at 3°C of warming are estimated to be 236 million (2021 dollars), approximately 38 percent greater than present-day. These results may inform decision-makers tasked with addressing climate risks, the public, and healthcare professionals preparing for treatment and prevention of LD.

Developing future climate projections begins with choosing future emissions scenarios. While scenarios are often based on storylines, here instead we produce a probabilistic multi-million-member ensemble of radiative forcing trajectories to assess the relevance of future forcing thresholds. We coupled a probabilistic database of future greenhouse gas emission scenarios with a probabilistically calibrated reduced complexity climate model. In 2100, we project median forcings of 5.1 watt per square meters (5th to 95th percentiles of 3.3 to 7.1), with roughly 0.5% probability of exceeding 8.5 watt per square meters, and a 1% probability of being lower than 2.6 watt per square meters. Although the probability of 8.5 watt per square meters scenarios is low, our results support their continued utility for calibrating damage functions, characterizing climate in the 22(nd) century (the probability of exceeding 8.5 watt per square meters increases to about 7% by 2150), and assessing low-probability/high-impact futures.

Evidence of the physical and economic impacts of climate change is a critical input to policy development and decision-making. In addition to the magnitude of potential impacts, detailed estimates of where, when, and to whom those damages may occur; the types of impacts that will be most damaging; uncertainties in these damages; and the ability of adaptation to reduce potential risks are all interconnected and important considerations. This study utilizes the reduced-complexity model, the Framework for Evaluating Damages and Impacts (FrEDI), to rapidly project economic and physical impacts of climate change across 10 000 future scenarios for multiple impact sectors, regions, and populations within the contiguous United States (US). Results from FrEDI show that net national damages increase overtime, with mean climate-driven damages estimated to reach USD 2.9 trillion (95 % confidence interval (CI): USD 510 billion to USD 12 trillion) annually by 2090. Detailed FrEDI results show that for the analyzed sectors the majority of annual long-term (e.g., 2090) damages are associated with climate change impacts to human health, including mortality attributable to climate-driven changes in temperature and air pollution (O3 and PM2.5) exposure. Regional results also show that annual long-term climate-driven damages vary geographically. The Southeast (all regions are as defined in Fig. 5) is projected to experience the largest annual damages per capita (mean: USD 9300 per person annually; 95 % CI: USD 1800-USD 37 000 per person annually), whereas the smallest damages per capita are expected in the Southwest (mean: USD 6300 per person annually; 95 % CI: USD 840-USD 27 000 per person annually). Climate change impacts may also broaden existing societal inequalities, with, for example, Black or African Americans being disproportionately affected by additional premature mortality from changes in air quality. Lastly, FrEDI projections are extended through 2300 to estimate the net present climate-driven damages within US borders from marginal changes in greenhouse gas emissions. Combined, this analysis provides the most detailed illustration to date of the distribution of climate change impacts within US borders.

High end emissions and forcing scenarios used to drive climate models provide key insights into possible high-risk climate change impacts in the 21st century and beyond. Given rapid and ongoing societal changes (e.g., population growth, energy demand, technology, etc.), debates are increasing on the continued relevance of higher forcing scenarios, such as those designed to reach 8.5 W/m2 by the end of the century (e.g., RCP8.5 and SSP5-8.5). Here, we determine an updated probability of exceeding 8.5 W/m2 by 2100 by generating a multi-million-member ensemble from a newly developed database of probabilistic greenhouse gas (GHG) emissions scenarios, augmented here with improved characterization of aerosols and minor GHGs, coupled with the newest version of a reduced complexity climate model, with parameter distributions calibrated to match the IPCC 6th Assessment Report. The probability of exceeding 8.5 W/m2 this century is estimated to be less than 1%: however, we discuss important rationales for the continued use of 8.5 W/m2 scenarios, including for generating high temperature scenarios for use in calibrating damage functions, characterizing climate in the 22nd century (probability of exceeding 8.5 W/m2 increases to ~7% by 2150), and assessing low-probability/high-impact futures.

Atmospheric methane directly affects surface temperatures and indirectly affects ozone, impacting human welfare, the economy, and environment. The social cost of methane (SC-CH4) metric estimates the costs associated with an additional marginal metric ton of emissions. Current SC-CH4 estimates do not consider the indirect impacts associated with ozone production from changes in methane. We use global model simulations and a new BenMAP webtool to estimate respiratory-related deaths associated with increases in ozone from a pulse of methane emissions in 2020. By using an approach consistent with the current SC-CH4 framework, we monetize and discount annual damages back to present day values. We estimate that the methane-ozone mechanism is attributable to 760 (95% CI: 330-1200) respiratory-related deaths per million metric tons of methane globally, for a global net present damage of $1800/mT (95% CI: $760-$2800/Mt CH4; 2% Ramsey discount rate); this would double the current SC-CH4 if included. These physical impacts are consistent with recent studies, but comparing direct costs is challenging. Economic damages are sensitive to uncertainties in the exposure and health risks associated with tropospheric ozone, assumptions about future projections of NOx emissions, socioeconomic conditions, and mortality rates, monetization parameters, and other factors. Our estimates are highly sensitive to uncertainties in ozone health risks. We also develop a reduced form model to test sensitivities to other parameters. The reduced form tool runs with a user-supplied emissions pulse, as well as socioeconomic and precursor projections, enabling future integration of the methane-ozone mechanism into the SC-CH4 modeling framework.

Methane directly contributes to air pollution, as an ozone precursor, and to climate change, generating physical and economic damages to different systems, namely agriculture, vegetation, energy, human health, or biodiversity. The methane-related damages to climate, measured as the Social Cost of Methane, and to human health have been analyzed by different studies and considered by government rulemaking in the last decades, but the ozone-related damages to crop revenues associated to methane emissions have not been incorporated to policy agenda. Using a combination of the Global Change Analysis Model and the TM5-FASST Scenario Screening Tool, we estimate that global marginal agricultural damages range from ~ 423 to 556 $2010/t-CH 4 , of which 98 $2010/t-CH 4 occur in the USA, which is the most affected region due to its role as a major crop producer, followed by China, EU-15, and India. These damages would represent 39–59% of the climate damages and 28–64% of the human health damages associated with methane emissions by previous studies. The marginal damages to crop revenues calculated in this study complement the damages from methane to climate and human health, and provides valuable information to be considered in future cost-benefits analyses.

This study provides estimates of climate change impacts on U.S. agricultural yields and the agricultural economy through the end of the 21st century, utilizing multiple climate scenarios. Results from a process-based crop model project future increases in wheat, grassland, and soybean yield due to climate change and atmospheric CO2 change; corn and sorghum show more muted responses. Results using yields from econometric models show less positive results. Both the econometric and process-based models tend to show more positive yields by the end of the century than several other similar studies. Using the process-based model to provide future yield estimates to an integrated agricultural sector model, the welfare gain is roughly $16B/year (2019 USD) for domestic producers and $6.2B/year for international trade, but domestic consumers lose $10.6B/year, resulting in a total welfare gain of $11.7B/year. When yield projections for major crops are drawn instead from econometric models, total welfare losses of more than $28B/year arise. Simulations using the process-based model as input to the agricultural sector model show large future production increases for soybean, wheat, and sorghum and large price reductions for corn and wheat. The most important factors are those about economic growth, flooding, international trade, and the type of yield model used. Somewhat less, but not insignificant factors include adaptation, livestock productivity, and damages from surface ozone, waterlogging, and pests and diseases.

Assessments of high-forcing climate scenarios provide unique insight into possible high-risk climate change impacts in the 21st century and beyond. Given rapid and ongoing societal changes (e.g., population growth, energy demand, technology, etc.), debates are increasing on the continued relevance of these 'high-forcing' scenarios, such as those designed to reach 8.5 W/m2 by the end of the century (e.g., RCP8.5 and SSP5-8.5). Here, we determine an updated probability of exceeding 8.5 W/m2 by 2100 by generating a multi-million-member ensemble from a newly developed database of probabilistic greenhouse gas (GHG) emissions scenarios, augmented here with improved characterization of aerosols and minor GHGs, coupled with the newest version of a reduced complexity climate model, with parameter distributions calibrated to match the IPCC 6th Assessment Report. The probability of exceeding 8.5 W/m2 this century is estimated to be less than 1%, however, we discuss important rationales for the continued use of 8.5 W/m2 scenarios, including for generating high temperature scenarios for use in calibrating damage functions, characterizing climate in the 22nd century (probability of exceeding 8.5 W/m2 increases to ~7% by 2150), and assessing low-probability/high-impact futures.

Workers in climate exposed industries such as agriculture, construction, and manufacturing face increased health risks of working on high temperature days and may make decisions to reduce work on high-heat days to mitigate this risk. Utilizing the American Time Use Survey (ATUS) for the period 2003 through 2018 and historical weather data, we model the relationship between daily temperature and time allocation, focusing on hours worked by high-risk laborers. The results indicate that labor allocation decisions are context specific and likely driven by supply-side factors. We do not find a significant relationship between temperature and hours worked during the Great Recession (2008-2014), perhaps due to high competition for employment, however during periods of economic growth (2003-2007, 2015-2018) we find a significant reduction in hours worked on high-heat days. During periods of economic growth, for every degree above 90 on a particular day, the average high-risk worker reduces their time devoted to work by about 2.6 minutes relative to a 90-degree day. This effect is expected to intensify in the future as temperatures rise. Applying the modeled relationships to climate projections through the end of century, we find that annual lost wages resulting from decreased time spent working on days over 90 degrees across the United States range from $36.7 to $80.0 billion in 2090 under intermediate and high emission futures, respectively.

Coccidioidomycosis, or valley fever, is an infectious fungal disease currently endemic to the southwestern United States. Symptoms of valley fever range in severity from flu-like illness to severe morbidity and mortality. Warming temperatures and changes in precipitation patterns may cause the area of endemicity to expand northward throughout the western United States, putting more people at risk for contracting valley fever. This may increase the health and economic burdens from this disease. We developed an approach to describe the relationship between climate conditions and valley fever incidence using historical data and generated projections of future incidence in response to both climate change and population trends using the Climate Change Impacts and Risk Analysis (CIRA) framework developed by the U.S. Environmental Protection Agency. We also developed a method to estimate economic impacts of valley fever that is based on case counts. For our 2000-15 baseline time period, we estimated annual medical costs, lost income, and economic welfare losses for valley fever in the United States were $400,000 per case, and the annual average total cost was $3.9 billion per year. For a high greenhouse gas emission scenario and accounting for population growth, we found that total annual costs for valley fever may increase up to 164% by year 2050 and up to 380% by 2090. By the end of the twenty-first century, valley fever may cost $620,000 per case and the annual average total cost may reach $18.5 billion per year. This work contributes to the broader effort to monetize climate change-attributable damages in the United States.

The potential effects of 21st century climate change on ozone (O-3) concentrations in the United States are investigated using global climate simulations to drive higher-resolution regional meteorological and chemical transport models. Community Earth System Model (CESM) and Coupled Model version 3 (CM3) simulations of the Representative Concentration Pathway 8.5 scenario are dynamically downscaled using the Weather Research and Forecasting model, and the resulting meteorological fields are used to drive the Community Multiscale Air Quality model. Air quality is modeled for five 11-year periods using both a 2011 air pollutant emission inventory and a future projection accounting for full implementation of promulgated regulatory controls. Across the U.S., CESM projects daily maximum temperatures during summer to increase 1-4 degrees C by 2050 and 2-7 degrees C by 2095, while CM3 projects warming of 2-7 degrees C by 2050 and 4-11 degrees C by 2095. The meteorological changes have geographically varying impacts on O-3 concentrations. Using the 2011 emissions dataset, O-3 increases 1-5 ppb in the central Great Plains and Midwest by 2050 and more than 10 ppb by 2095, but it remains unchanged or even decreases in the Gulf Coast, Maine, and parts of the Southwest. Using the projected emissions, modeled increases are attenuated while decreases are amplified, indicating that planned air pollution control measures ameliorate the ozone climate penalty. The relationships between changes in maximum temperature and changes in O-3 concentrations are examined spatially and quantified to explore the potential for developing an efficient approach for estimating air quality impacts of other future climate scenarios. Implications: The effects of climate change on ozone air quality in the United States are investigated using two global climate model simulations of a high warming scenario for five decadal periods in the 21st century. Warming summer temperatures simulated under both models lead to higher ozone concentrations in some regions, with the magnitude of the change increasing with temperature over the century. The magnitude and spatial extent of the increases are attenuated under a future emissions projection that accounts for regulatory controls. Regional linear regression relationships are developed as a first step toward development of a reduced form model for efficient estimation of the health impacts attributable to changes in air quality resulting from a climate change scenario.

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.

Wildfire activity in the western United States (US) has been increasing, a trend that has been correlated with changing patterns of temperature and precipitation associated with climate change. Health effects associated with exposure to wildfire smoke and fine particulate matter (PM2.5) include short- and long-term premature mortality, hospital admissions, emergency department visits, and other respiratory and cardiovascular incidents. We estimate PM2.5 exposure and health impacts for the entire continental US from current and future western US wildfire activity projected for a range of future climate scenarios through the 21st century. We use a simulation approach to estimate wildfire activity, area burned, fine particulate emissions, air quality concentrations, health effects, and economic valuation of health effects, using established and novel methodologies. We find that climatic factors increase wildfire pollutant emissions by an average of 0.40% per year over the 2006-2100 period under Representative Concentration Pathway (RCP) 4.5 (lower emissions scenarios) and 0.71% per year for RCP8.5. As a consequence, spatially weighted wildfire PM2.5 concentrations more than double for some climate model projections by the end of the 21st century. PM2.5 exposure changes, combined with population projections, result in a wildfire PM2.5-related premature mortality excess burden in the 2090 RCP8.5 scenario that is roughly 3.5 times larger than in the baseline period. The combined effect of increased wildfire activity, population growth, and increase in the valuation of avoided risk of premature mortality over time results in a large increase in total economic impact of wildfire-related PM2.5 mortality and morbidity in the continental US, from roughly $7 billion per year in the baseline period to roughly $36 billion per year in 2090 for RCP4.5, and $43 billion per year in RCP8.5. The climate effect alone accounts for a roughly 60% increase in wildfire PM2.5-related premature mortality in the RCP8.5 scenario, relative to baseline conditions.

BackgroundExtreme heat exposure can lead to premature death. Climate change is expected to increase the frequency, intensity, and duration of extreme heat events, resulting in many additional heat-related deaths globally, as well as changing the nature of extreme cold events. At the same time, vulnerability to extreme heat has decreased over time, probably due to a combination of physiological, behavioural, infrastructural, and technological adaptations. We aimed to account for these changes in vulnerability and avoid overstated projections for temperature-related mortality. We used the historical observed decrease in vulnerability to improve future mortality estimates.MethodsWe used historical mortality and temperature data from 208 US cities to quantify how observed changes in vulnerability from 1973 to 2013 affected projections of temperature-related mortality under various climate scenarios. We used geographically structured meta-regression to characterise the relationship between temperature and mortality for these urban populations over the specified time period. We then used the fitted relationships to project mortality under future climate conditions.FindingsBetween Oct 26, 2018, and March 9, 2020, we established that differences in vulnerability to temperature were geographically structured. Vulnerability decreased over time in most areas. US mortalities projected from a 2°C increase in mean temperature decreased by more than 97% when using 2003–13 data compared with 1973–82 data. However, these benefits declined with increasing temperatures, with a 6°C increase showing only an 84% decline in projected mortality based on 2003–13 data.InterpretationEven after accounting for adaptation, the projected effects of climate change on premature mortality constitute a substantial public health risk. Our work suggests large increases in temperature will require additional mitigation to avoid excess mortality from heat events, even in areas with high air conditioning coverage in place.FundingThe US Environmental Protection Agency and Abt Associates.