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Art x Climate was the first-ever gallery of visual art to be included in the National Climate Assessment. This letter outlines the purpose and process of Art x Climate and highlights three Art x Climate artists and their work. The letter concludes with lessons learned from this project: the need for cross-disciplinary respect among the arts and sciences, the wide range of themes and artworks centered around climate change, and the ability of art to facilitate new collaborations and bring more people into the climate change conversation.

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.In this Article, modelling results from a consistent set of sectoral climate change impact models, covering 22 impact sectors of the United States, are summarized. Findings are complex, but largely negative and expensive.

Measurements from several ocean cores reveal that ocean warmth persisted throughout the late Miocene epoch despite CO 2 levels of only 200–350 p.p.m.v., probably driven by a deep thermocline that isolated climate responses from CO 2 variations. When ocean temperature and atmospheric carbon dioxide delinked Geological records of past climate provide the only opportunity to investigate Earth's response to large variations in atmospheric carbon dioxide concentrations. During the late Miocene, between 12 million and 5 million years ago, atmospheric CO 2 levels of only 200 to 350 parts per million by volume were accompanied by almost ice-free conditions in the Northern Hemisphere and the continents were warmer than they are at present, raising questions about the persistence of CO 2 –climate couplings. Using measurements from several ocean cores, LaRiviere et al . show that ocean warmth persisted throughout the late Miocene, probably driven by a thick thermocline that isolated climate responses from CO 2 variations. As the depth of the thermocline declined during the late Miocene, the more familiar relationship between CO 2 and climate was established. Deep-time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration (that is, the atmospheric partial pressure of CO 2 , p CO 2 ) 1 . Although past studies have explored these responses during portions of the Cenozoic era (the most recent 65.5 million years (Myr) of Earth history), comparatively little is known about the climate of the late Miocene (∼12–5 Myr ago), an interval with p CO 2 values of only 200–350 parts per million by volume but nearly ice-free conditions in the Northern Hemisphere 2 , 3 and warmer-than-modern temperatures on the continents 4 . Here we present quantitative geochemical sea surface temperature estimates from the Miocene mid-latitude North Pacific Ocean, and show that oceanic warmth persisted throughout the interval of low p CO 2 ∼12–5 Myr ago. We also present new stable isotope measurements from the western equatorial Pacific that, in conjunction with previously published data 5 , 6 , 7 , 8 , 9 , 10 , reveal a long-term trend of thermocline shoaling in the equatorial Pacific since ∼13 Myr ago. We propose that a relatively deep global thermocline, reductions in low-latitude gradients in sea surface temperature, and cloud and water vapour feedbacks may help to explain the warmth of the late Miocene. Additional shoaling of the thermocline after 5 Myr ago probably explains the stronger coupling between p CO 2 , sea surface temperatures and climate that is characteristic of the more recent Pliocene and Pleistocene epochs 11 , 12 .

The U.S. Southwest is projected to experience increasing aridity due to climate change. We quantify the resulting impacts on ambient dust levels and public health using methods consistent with the Environmental Protection Agency's Climate Change Impacts and Risk Analysis framework. We first demonstrate that U.S. Southwest fine (PM2.5) and coarse (PM2.5‐10) dust levels are strongly sensitive to variability in the 2‐month Standardized Precipitation‐Evapotranspiration Index across southwestern North America. We then estimate potential changes in dust levels through 2099 by applying the observed sensitivities to downscaled meteorological output projected by six climate models following an intermediate (Representative Concentration Pathway 4.5, RCP4.5) and a high (RCP8.5) greenhouse gas concentration scenario. By 2080–2099 under RCP8.5 relative to 1986–2005 in the U.S. Southwest: (1) Fine dust levels could increase by 57%, and fine dust‐attributable all‐cause mortality and hospitalizations could increase by 230% and 360%, respectively; (2) coarse dust levels could increase by 38%, and coarse dust‐attributable cardiovascular mortality and asthma emergency department visits could increase by 210% and 88%, respectively; (3) climate‐driven changes in dust concentrations can account for 34–47% of these health impacts, with the rest due to increases in population and baseline incidence rates; and (4) economic damages of the health impacts could total$47 billion per year additional to the 1986–2005 value of $ 13 billion per year. Compared to national‐scale climate impacts projected for other U.S. sectors using the Climate Change Impacts and Risk Analysis framework, dust‐related mortality ranks fourth behind extreme temperature‐related mortality, labor productivity decline, and coastal property loss. Plain Language Summary The southwestern United States is projected to experience severe, multidecadal droughts due to human‐caused climate change. Mineral dust particles are a major contributor to air pollution in this region due to abundant deserts and drylands. To what extent could airborne dust levels increase as a result of the projected drought conditions? To answer this question, we first investigate the influence of drought conditions across southwestern North America on dust activity in recent years. We then use the observed relationships between dust and droughts to estimate future changes in dust levels—and the associated excess deaths and illnesses—through the end of the century, using projections of temperature and precipitation from global climate models following two plausible (high and intermediate) greenhouse gas emissions scenarios. Under the high emissions scenario, premature mortality associated with dust exposure increases by 220% and hospitalization increases by 160% toward the end of this century, due to combined increases in population, disease rates, and dust levels. The annual economic damages of these health impacts are estimated to be$47 billion per year additional to the present‐day value of $ 13 billion per year, making climate‐driven changes in dust concentrations one of the costliest impacts projected for the United States so far. Key Points Increasing aridity may cause dust levels in the U.S. Southwest to rise by 40% in 2090 under a high greenhouse gas concentration scenario Dust‐related mortality could increase by 220% in 2090 under the high scenario Estimated economic damages from dust‐related mortality make this one of the costliest climate impacts projected for the United States so far

Pollen is an important environmental cause of allergic asthma episodes. Prior work has established a proof of concept for assessing projected climate change impacts on future oak pollen exposure and associated health impacts. This paper uses additional monitor data and epidemiologic functions to extend prior analyses, reporting new estimates of the current and projected future health burden of oak, birch, and grass pollen across the contiguous United States. Our results suggest that tree pollen in the spring currently accounts for between 25,000 and 50,000 pollen‐related asthma emergency department (ED) visits annually (95% confidence interval: 14,000 to 100,000), roughly two thirds of which occur among people under age 18. Grass pollen in the summer season currently accounts for less than 10,000 cases annually (95% confidence interval: 4,000 to 16,000). Compared to a baseline with 21st century population growth but constant pollen, future temperature and precipitation show an increase in ED visits of 14% in 2090 for a higher greenhouse gas emissions scenario, but only 8% for a moderate emissions scenario, reflecting projected increases in pollen season length. Grass pollen, which is more sensitive to changes in climatic conditions, is a primary contributor to future ED visits, with the largest effects in the Northeast, Midwest, and Southern Great Plains regions. More complete assessment of the current and future health burden of pollen is limited by the availability of data on pollen types (e.g., ragweed), other health effects (e.g., other respiratory disease), and economic consequences (e.g., medication costs). Key Points We link pollen, climate, and epidemiological data to estimate the health burden of oak, birch, and grass pollen across the contiguous United States We found that 35,000 to 60,000 asthma emergency department visits (two thirds of these among children) may be linked with pollen each year We project that future climate changes could increase pollen‐related asthma emergency department visits by 14% in 2090

Increasing atmospheric carbon dioxide levels, higher temperatures, altered precipitation patterns, and other climate change impacts have already begun to affect US agriculture and forestry, with impacts expected to become more substantial in the future. There have been numerous studies of climate change impacts on agriculture or forestry, but relatively little research examining the long-term net impacts of a stabilization scenario relative to a case with unabated climate change. We provide an analysis of the potential benefits of global climate change mitigation for US agriculture and forestry through 2100, accounting for landowner decisions regarding land use, crop mix, and management practices. The analytic approach involves a combination of climate models, a crop process model (EPIC), a dynamic vegetation model used for forests (MC1), and an economic model of the US forestry and agricultural sector (FASOM-GHG). We find substantial impacts on productivity, commodity markets, and consumer and producer welfare for the stabilization scenario relative to unabated climate change, though the magnitude and direction of impacts vary across regions and commodities. Although there is variability in welfare impacts across climate simulations, we find positive net benefits from stabilization in all cases, with cumulative impacts ranging from $32.7 billion to $54.5 billion over the period 2015-2100. Our estimates contribute to the literature on potential benefits of GHG mitigation and can help inform policy decisions weighing alternative mitigation and adaptation actions.

Future climate change is expected to lengthen and intensify pollen seasons in the U.S., potentially increasing incidence of allergic asthma. We developed a proof‐of‐concept approach for estimating asthma emergency department (ED) visits in the U.S. associated with present‐day and climate‐induced changes in oak pollen. We estimated oak pollen season length for moderate (Representative Concentration Pathway (RCP) 4.5) and severe climate change scenarios (RCP8.5) through 2090 using five climate models and published relationships between temperature, precipitation, and oak pollen season length. We calculated asthma ED visit counts associated with 1994–2010 average oak pollen concentrations and simulated future oak pollen season length changes using the Environmental Benefits Mapping and Analysis Program, driven by epidemiologically derived concentration‐response relationships. Oak pollen was associated with 21,200 (95% confidence interval, 10,000–35,200) asthma ED visits in the Northeast, Southeast, and Midwest U.S. in 2010, with damages valued at$10.4 million. Nearly 70% of these occurred among children age <18 years. Severe climate change could increase oak pollen season length and associated asthma ED visits by 5% and 10% on average in 2050 and 2090, with a marginal net present value through 2090 of $ 10.4 million (additional to the baseline value of $346.2 million). Moderate versus severe climate change could avoid >50% of the additional oak pollen‐related asthma ED visits in 2090. Despite several key uncertainties and limitations, these results suggest that aeroallergens pose a substantial U.S. public health burden, that climate change could increase U.S. allergic disease incidence, and that mitigating climate change may have benefits from avoided pollen‐related health impacts. Key Points Aeroallergens pose a substantial U.S. public health burden Climate change could increase U.S. allergic disease incidence Mitigating climate change may have benefits from avoided pollen‐related health impacts

Key Points Despite improvements to better characterize risk in climate assessments, scientists' certainty in findings is often misinterpreted U.S. climate assessments often report high confidence and likelihood findings and rarely report low certainty, potentially severe impacts Alternative representations of calibrated language may alleviate confusion caused by the common use of colloquial likelihood terms The use of calibrated language in climate assessments has evolved over time and is an important tool for better characterizing climate risk. Despite improvements in communication, likelihood and confidence terms continue to be misinterpreted by nontechnical audiences. Public understanding of scientific certainty in climate impacts, particularly at the extreme tails of likelihood distribution, is inadequate. This study evaluates the use of calibrated language in the four most recent U.S. climate assessments. Across the assessments, there is inconsistent use, definition, location, and formatting designating a term as calibrated. Authors include additional, undefined certainty categories bridging qualitative confidence categories (e.g., \"medium to high\") and likelihood terms with no associated statistical value (e.g., \"highly likely\"). Confidence and likelihood levels are more frequently reported for terms at the high end of certainty distributions, with at least 70% of all instances of confidence terms reporting high or very high confidence in three of the assessments. Almost all (>98%) likelihood language reported is in the likely (>66%) category or above and no likelihood terms below 50% are reported in any of the assessment's Key Messages. There is significant room for improvement in the representation of likelihood, as the word “likely” is frequently used with ambiguous intent; at least half of all instances of likelihood terms are used with noncalibrated, potentially colloquial intent in three of the assessments. The study concludes with a set of recommendations for improving the use of calibrated language and communication of risk in the development of future assessment products. Plain Language Summary It is important for scientists to describe how certain they are about climate change science so that people can make informed decisions about how to reduce greenhouse gas emissions or prepare for climate impacts. Scientists who evaluate and summarize key findings from a broad review of climate change literature describe their certainty in these findings in scientific assessments using calibrated language. Calibrated language uses specific terminology to express varying degrees of confidence in a statement and how statistically likely an effect or impact is to occur. However, many people outside scientific fields are unfamiliar with calibrated language and often misinterpret their meaning. This study identifies three issues with how calibrated language is used in U.S. climate assessments. First, there is inconsistent use of calibrated language across reports, with authors sometimes using terms that are not defined. Second, these reports focus on findings with high confidence and high likelihood, potentially leaving out information on low probability but highly dangerous impacts. Finally, use of likelihood terms is particularly problematic because the word “likely” is commonly used as part of everyday conversation and different people assign different definitions to it based on their own language, culture, or field of work. It is therefore hard for readers to know, when they come across the word “likely,” whether that word is meant colloquially or whether it has a specific statistical definition associated with it. This paper suggests some ways in which future U.S. climate assessments can be improved to address these three issues.