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3 - 1 **CHAPTER 3**  **DEFINING THE CLIMATE CHANGE PROBLEM AND R** **ATIONALE FOR RULEMAK ING**  **3 .1**  **Overview of Climate Chan ge Impacts from GHG Emissions**  In 2009, the EPA Administrator found that elevated concentrations of greenhouse gases in the atmosphere may reasonably be anticipated both to endanger public health and to endanger public welfare. It is these adverse impacts that make it necessary for EPA to regulate greenhouse gases from EGU sources. Th i s proposed rule is designed to minimize emissions of greenhouse gases, minimiz e the rate of increase of concentrations of these gases, and therefore reduc e the risk of adverse effects. As the analysis prese nted in Chapter 5 shows, e xisting and anticipated economic conditions in the marketplace will lead electricity generators to choose technologies that meet the proposed standards. However, r ather than relying solely on changeable energy market conditions to provide low emissions from new power plants in the future , though this rule, EPA ensures that new electricity generation will be clean generation. This chapter summarizes the adverse effects on public health and public welfare detailed in the 2009 Endang erment Finding. 1 The major assessments by the U.S. Global C hange Research Program (USGCRP), the Intergovernmental Panel on Climate Change (IPCC), and the National Research Council (NRC) served as the primary scientific basis for these effects. **3 .1.1**  **Publi c Health**  Climate change threatens public health in a number of ways: direct temperature effects, air quality effects, the potential for changes in vector - borne diseases, and the potential for changes in the severity and frequency of extreme weather events. Additionally, susceptible populations may be particularly at risk. Each of these effects will be addressed in turn in this section , based on the 2009 Endangerment Finding . Regarding direct temperature changes, it has already been estimated that unusually hot days and heat waves are becoming more frequent, and that unusually cold days are becoming less frequent. Heat is already the leading cause of weather - related deaths in t he United States. In the future, severe heat waves are projected to intensify in magnitude and duration over the portions of the United States where these events already occur. Heat waves are associated with

1 Endangerment and Caus e or Contribute Findings for Greenhouse Gase s Under Section 202(a) of the Clean Air Act , 74 Fed. Reg. 66,496 (Dec. 15, 2009).***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 2 marked short -term increases in mortality. Hot te mperatures have also been associated with increased morbidity. The projected warming is therefore projected to increase heat related mortality and morbidity, especially among the elderly, young, and frail. The populations most sensitive to hot temperatures are older adults, the chronically sick, the very young, citydwellers, those taking medications that disrupt thermoregulation, the mentally ill, those lacking access to air conditioning, those working or playing outdoors, and socially isolated persons. As warming increases over time, these adverse effects would be expected to increase as the serious heat events become more serious. Increases in temperature are also expected to lead to some reduction in the risk of death related to extreme cold. It is not clear whether reduced mortality in the United States from cold would be greater or less than increased heat - related mortality in the United States due to climate change. However, there is a risk that projections of cold - related deaths, and the potential fo r decreasing their numbers due to warmer winters, can be overestimated unless they take into account the effects of season and influenza, which is not strongly associated with monthly winter temperature. In addition, the latest USGCRP report (2009) refers to a study (Medina - Ramon and Schwartz, 2007) that analyzed daily mortality and weather data in 50 U.S. cities from 1989 to 2000 and found that, on average, cold snaps in the United States increased death rates by 1.6 percent, while heat waves triggered a 5 .7 percent increase in death rates. The study concludes that increases in heat - related mortality due to global warming in the United States are unlikely to be compensated for by decreases in cold - related mortality. Regarding air quality effects, increases in regional ozone pollution relative to ozone levels without climate change are expected due to higher temperatures and weaker circulation in the United States relative to air quality levels without climate change. Climate change is expected to increase regional ozone pollution, with associated risks in respiratory illnesses and premature death. In addition to human health effects, tropospheric ozone has significant adverse effects on crop yields, pasture and forest growth, and species composition. Modeli ng studies discussed in EPA’s Interim Assessment (2009) show that simulated climate change causes increases in summertime ozone concentrations over substantial regions of the country, though this was not uniform, and some areas showed little change or decr eases, though the decreases tend to be less pronounced than the increases. For those regions that showed climate - induced increases, the increase in maximum daily 8 - hour average ozone concentration, a key metric for regulating U.S. air quality, was in the r ange of 2 to 8 ppb, averaged over the summer season. The increases were substantially greater than this during***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 3 the peak pollution episodes that tend to occur over a number of days each summer. The overall effect of climate change was projected to increase ozone levels, compared to what would occur without this climate change, over broad areas of the country, especially on the highest ozone days and in the largest metropolitan areas with the worst ozone problems. Ozone decreases are projected to be less pron ounced, and generally to be limited to some regions of the country with smaller population. In addition to impacts on heat - related mortality and air quality, there is also the potential for increased deaths, injuries, infectious diseases, and stress - relat ed disorders and other adverse effects associated with social disruption and migration from more frequent extreme weather. Vulnerability to these disasters depends on the attributes of the people at risk and on broader social and environmental factors. In creases in the frequency of heavy precipitation events are associated with increased risk of deaths and injuries as well as infectious, respiratory, and skin diseases. Floods are low probability, high - impact events that can overwhelm physical infrastructur e, human resilience, and social organization. Flood health impacts include deaths, injuries, infectious diseases, intoxications, and mental health problems. Increases in tropical cyclone intensity are linked to increases in the risk of deaths, injuries, w aterborne and food borne diseases, as well as post -traumatic stress disorders. Drowning by storm surge, heightened by rising sea levels and more intense storms (as projected by IPCC), is the major killer in coastal storms where there are large numbers of d eaths. Flooding can cause health impacts including direct injuries as well as increased incidence of waterborne diseases . According to the assessment literature, there will also likely be an increase in the spread of several food and water- borne pathogens among susceptible populations depending on the pathogens’ survival, persistence, habitat range and transmission under changing climate and environmental conditions. Food borne diseases show some relationship with temperature, and the range of some zoonoti c disease carriers such as the Lyme disease carrying tick may increase with temperature. Climate change, including changes in carbon dioxide concentrations, could impact the production, distribution, dispersion , and allergenicity of aeroallergens and the growth and distribution of weeds, grasses, and trees that produce them. These changes in aeroallergens***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 4 and subsequent human exposures could affect the prevalence and severity of allergy symptoms. However, the scientific literature does not provide definiti ve data or conclusions on how climate change might impact aeroallergens and subsequently the prevalence of allergenic illnesses in the United States. It has generally been observed that the presence of elevated carbon dioxide concentrations and temperature s stimulate plants to increase photosynthesis, biomass, water use efficiency, and reproductive effort. The IPCC concluded that pollens are likely to increase with elevated temperature and carbon dioxide. **3 .**  **1.2 Public Welfare**  As with public health, there are multiple pathways in which the greenhouse gas air pollution and resultant climate change affect climate - sensitive sectors. These sectors include food production and agriculture; forestry; water resources; sea level rise and coastal areas; energy, infra structure, and settlements; and ecosystems and wildlife. Impacts also arise from climate change occurring outside of the United States, such as national security concerns for the United States that may arise as a result of climate change impacts in other r egions of the world. Each of these effects will be addressed in turn in this section , based on the 2009 Finding. Regarding food production and agriculture, e levated carbon dioxide concentrations can have a stimulatory effect, as may modest temperature incr eases and a longer growing season that results. However, elevated carbon dioxide concentrations may also enhance pest and weed growth. In addition, higher temperature increases, changing precipitation patterns and variability, and any increases in ground - l evel ozone induced by higher temperatures, can work to counteract any direct stimulatory carbon dioxide effect, as well as lead to their own adverse impacts. A USGCRP report (2009) concluded that while for some crops such as grain and oilseed crops there m ay be a beneficial effect overall in the next couple decades, as temperature rises, these crops will increasingly begin to experience failure, especially if climate variability increases and precipitation lessens or becomes more variable. Changes in the intensity and frequency of extreme weather events such as droughts and heavy storms have the potential to have serious negative impact on U.S. food production and agriculture. Changing precipitation patterns, in addition to increasing temperatures and longer growing seasons, can change the demand for irrigation requirements, potentially increasing irrigation demand. With respect to livestock, higher temperatures will very likely reduce livestock production during the summer season in some areas, but t hese losses will very likely be partially offset by warmer temperatures during the winter season. The impact on livestock***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 5 productivity due to increased variability in weather patterns will likely be far greater than effects associated with the average chan ge in climatic conditions. For the forestry sector there are similar factors to consider. There is the potential for beneficial effects due to elevated c oncentrations of carbon dioxide, increased temperature s , and nitrogen deposition, but there is also the potential for adverse effects from increasing temperatures, changing precipitation patterns, increased insects and disease, and the potential for more frequent and severe extreme weather events. According to the science assessment reports on which the Adm inistrator relied for the 2009 Finding, climate change has very likely increased the size and number of wildfires, insect outbreaks, and tree mortality in the Interior West, the Southwest, and Alaska, and will continue to do so. If existing trends in prec ipitation continue, it is expected that forest productivity will likely decrease in the Interior West, the Southwest, eastern portions of the Southeast, and Alaska, and that forest productivity will likely increase in the northeastern United States, the La ke States, and in western portions of the Southeast. An increase in drought events will very likely reduce forest productivity wherever such events occur. The sensitivity of water resources to climate change is very important given the increasing demand for adequate water supplies and services for agricultural, municipal, and energy and industrial uses, and the current strains on this resource in many parts of the country. According to the assessment literature, climate change has already altered, and will likely continue to alter, the water cycle, affecting where, when, and how much water is available for all uses. With higher temperatures, the water - holding capacity of the atmosphere and evaporation into the atmosphere increase, and this favors increased climate variability, with more intense precipitation and more droughts. Climate change is causing and will increasingly cause shrinking snowpack induced by increasing temperature. In the western United States, there is already well - documented evidence of shrinking snowpack due to warming. Earlier meltings, with increased runoff in the winter and early spring, increase flood concerns and also result in substantially decreased summer flows. This pattern of reduced snowpack and changes to the flow regime pose very serious risks to major population regions, such as California, that rely on snowmelt - dominated watersheds for their water supply. While increased precipitation is expected to increase water flow levels in some eastern areas, this may be tempered by i ncreased variability in the***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 6 precipitation and the accompanying increased risk of floods and other concerns such as water pollution. Climate change will likely further constrain already over - allocated water resources in some regions of the United States, i ncreasing competition among agricultural, municipal, industrial, and ecological uses. Although water management practices in the United States are generally advanced, particularly in the West, the reliance on past conditions as the basis for current and fu ture planning may no longer be appropriate, as climate change increasingly creates conditions well outside of historical observations. Increased incidence of extreme weather and floods may also overwhelm or damage water treatment and management systems, re sulting in water quality impairments. According to the assessment literature, sea level is rising along much of the U.S. coast and the rate of change will very likely increase in the future, exacerbating the impacts of progressive inundation, storm - surge flooding, and shoreline erosion. A large percentage of the U.S. po pulation lives in these coastal areas . The most vulnerable areas are the Atlantic and Gulf Coasts, the Pacific Islands, and parts of Alaska. Cities such as New Orleans, Miami, and New York a re particularly at risk, and could have difficulty coping with the sea level rise projected by the end of the century under a higher emissions scenario. Population growth and the rising value of infrastructure increases the vulnerability to climate variabi lity and future climate change in coastal areas. Adverse impacts on islands present concerns for Hawaii and the U.S. territories. Reductions in Arctic sea ice increases extreme coastal erosion in Alaska, due to the increased exposure of the coastline to st rong wave action. In the Great Lakes, where sea level rise is not a concern, both extremely high and low water levels resulting from changes to the hydrological cycle have been damaging and disruptive to shoreline communities. Coastal wetland loss is bein g observed in the United States where these ecosystems are squeezed between natural and artificial landward boundaries and rising sea levels. Up to 21 percent of the remaining coastal wetlands in the U.S. mid - Atlantic region are potentially at risk of inun dation between 2000 and 2100. Coastal habitats will likely be increasingly stressed by climate change impacts interacting with development and pollution. Although increases in mean sea level over the 21st century and beyond will inundate unprotected, low - lying areas, the most devastating impacts are likely to be associated with storm surge. Superimposed on expected rates of sea level rise, projected storm i ntensity, wave height, and storm surge suggest more severe coastal flooding and erosion hazards. Higher sea***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 7 level provides an elevated base for storm surges to build upon and diminishes the rate at which low - lying areas drain, thereby increasing the risk o f flooding from rainstorms. In New York City and Long Island, flooding from a combination of sea level rise and storm surge could be several meters deep. Projections suggest that the return period of a 100 -year flood event in this area might be reduced to 4–60 years by the 2080s. Additionally, some major urban centers in the United States, such as areas of New Orleans are situated in low - lying flood plains, presenting increased risk from storm surges. With respect to infrastructure, climate change vulnerab ilities of industry, settlement , and society are mainly related to changes in intensity and frequency of extreme weather events rather than to gradual climate change. Extreme weather events could threaten U.S. energy infrastructure (transmission and distri bution), transportation infrastructure (roads, bridges, airports and seaports), water infrastructure, and other built aspects of human settlements. Moreover, soil subsidence caused by the melting of permafrost in the Arctic region is a risk to gas and oil pipelines, electrical transmission towers, roads, and water systems. Within settlements experiencing climate change stressors, certain parts of the population may be especially vulnerable based on their circumstances. These include the poor, the elderly, the very young, those already in poor health, the disabled, those living alone, and/or indigenous populations dependent on one or a few resources. In Alaska, indigenous communities are likely to experience disruptive impacts, including shifts in the range or abundance of wild species crucial to their livelihoods and well - being. Climate change is exerting major influences on natural environments and biodiversity, and these influences are generally expected to grow with increased warming. Observed changes in the life cycles of plants and animals include shifts in habitat ranges, timing of migration patterns, and changes in reproductive timing and behavior. The underlying assessment literature finds with high confidence that substantial changes in the structu re and functioning of terrestrial ecosystems are very likely to occur with a global warming greater than 2 to 3 °C above pre - industrial levels, with predominantly negative consequences for biodiversity and the provisioning of ecosystem goods and services. With global average temperature changes above 2 °C, many terrestrial, freshwater, and marine species (particularly endemic species) are at a far greater risk of extinction than in the geological past. Climate change and ocean acidification will likely impa ir a wide range of planktonic and other marine calcifiers such as corals. Even without ocean acidification effects,***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 8 increases in sea surface temperature of about 1 –3 °C are projected to result in more frequent coral bleaching events and widespread mortalit y. In the Arctic, wildlife faces great challenges from the effects of climatic warming, as projected reductions in sea ice will drastically shrink marine habitat for polar bears, ice - inhabiting seals, and other animals. Some common forest types are projected to expand, others are projected to contract, and others, such as spruce - fir, are likely to disappear from the contiguous United States. Changes in plant species composition in response to climate change can increase ecosystem vulnerability to other disturbances, including wildfires and biological invasion. Disturbances such as wildfires and insect outbreaks are increasing in the United States and are likely to intensify in a warmer future with warmer winters, drier soils and longer growing seasons. The areal extent of drought - limited ecosystems is projected to increase 11 percent per °C warming in the United States. In California, temperature increases greater than 2°C may lead to conversion of shrubland into desert and grassland ecosystems and evergreen conifer forests into mixed deciduous forests. Greater intensity of extreme events may alter disturbance regimes in coastal ecosystems leading to changes in diversity and ecosystem functioning. Species inhabiting salt marshes, mangroves, and coral reefs ar e likely to be particularly vulnerable to these effects. According to the USGCRP report of June 2009 and other sources, climate change impacts in certain regions of the world may exacerbate problems that raise humanitarian, trade, and national security i ssues for the United States. 2 The IPCC identifies the most vulnerable world regions as the Arctic, because of the effects of high rates of projected warming on natural systems; Africa, especially the sub - Saharan region, because of current low adaptive capa city as well as climate change; small islands, due to high exposure of population and infrastructure to risk of sea - level rise and increased storm surge; and Asian mega - deltas due to large populations and high exposure to sea level rise, storm surge, and r iver flooding. Climate change has been described as a potential threat multiplier with regard to national security issues. While some of these international risks do not readily lend themselve s to precise analyses or future projections, given the unavoidab le global nature of t he climate change problem it is appropriate and prudent to consider how impacts in other world regions may present risks to the U.S. population.
2 ‘‘In an increasingly interdependent world, U.S. vulnerability to climate change is linked to the fates of other nations. For example, conflicts or mass migrations of people resulting from food scarcity and other resource limits, health impacts or environmental stresses in other parts of the world could threaten U.S. national security.’’ (Karl et al., 2009).***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 9 **3 .1.**  **3 Recent Assessments**  Since the Endangerment Finding was released, more recent assessments have produced similar conclusions to those of the assessments upon which the Finding was based. In May 2010, the NRC published its comprehensive assessment, “Advancing the Science of Climate Change” (2010). It concluded that “climate change is occurring, is caused largely by human activities, and poses significant risks for — and in many cases is already affecting — a broad range of human and natural systems.” Furthermore, the NRC stated that this conclusion is based on findings that are “consistent with the conclusions of recent assessments by the U.S. Global Change Research Program, the Intergovernmental Panel on Climate Change’s Fourth Assessment Report, and other assessments of the state of scientific knowledge on climate change.” These are t he same assessments that served as the primary scientific references underlying the Administrator’s Endangerment Finding. Another NRC assessment, “Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millen n ia , ” was publish ed in 2011. This report found that climate change due to carbon dioxide emissions will persist for many centuries. The report also estimate a number of specific climate change impacts, finding that every degree Celsius of warming could lead to increases in the heaviest 15 percent of daily rainfalls of 3 to 10 percent, decreases of 5 to 15 percent in yields for a number of crops (absent adaptation measures that do not presently exist), decreases of Arctic sea ice extent of 25 percent in September and 15 perc ent annually averaged, along with changes in precipitation and stream flow of 5 to 10 percent in many regions and river basins. The assessment also found that for an increase of 4 degrees C nearly all land areas would experience average summers warmer than all but 5 percent of summers in the 20 th century, that for an increase of 1 to 2 degrees C the area burnt by wildfires in western North America will likely more than double, that coral bleaching and erosion will increase due both to warming and ocean acid ification, and that sea level will rise 1.6 to 3.3 feet by 2100 in a 3 degree C scenario. The assessment notes that many important aspects of climate change are difficult to quantify but that the risk of adverse impacts is likely to increase with increasin g temperature, and that the risk of surprises can be expected to increase with the duration and magnitude of warming. In the 2010 report cited above, the NRC stated that some of the largest potential risks associated with future climate change may come not from relatively smooth changes that are reasonably well understood, but from extreme events, abrupt changes, and surprises that might occur when climate or environmental system thresholds are crossed. Examples cited as warranting more research include th e release of large quantities of GHGs stored in permafrost***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 10 (frozen soils) across the Arctic, rapid disintegration of the major ice s heets , irreversible drying and desertification in the subtropics, changes in ocean circulation, and the rapid release of des tabilized methane hydrates in the oceans . On ocean acidification, t he same report noted the potential for broad, “catastrophic” impacts on marine ecosystems. O cean acidity has increased 25 percent since p re - industrial times, and is projected to continue increasing . By the time atmospheric CO 2 content doub les over its preindustrial value, there would be virtually no place left in the ocean that can sustain coral reef growth. Ocean acidification could have dramatic consequences for polar food webs includ ing salmon, the report said. Importantly, these recent NRC assessments represent another independent and critical inquiry of the state of climate change science, separate and apart from the previous IPCC, NRC, and USGCRP assessments. **3 .2**  **References** 40 CFR Chapter I [EPA– HQ –OAR– 2009–0171; FRL

–9091–8] RIN 2060–ZA14, “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act , ” Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulat ions. Karl, T., J. Melillo, and T. Peterson (Eds.) (2009) . Global Climate Change Impacts in the United States . Cambridge University Press, Cambridge, United Kingdom. Medina - Ramon, M. and J. Schwartz, 2007: Temperature, temperature extremes, and mortality: a study of acclimatization and effect modification in 50 U.S. cities. Occupational and Environmental Medicine, 64(12), 827 - 833. National Research Council ( 2010) . Advancing the Science of Climate Change . National Academy Press . Washington, DC. National Research Council (2011) . Climate Stabilization Targets : Emissions, Concentrations, and Impacts over Decades to Mille n nia . National Academy Press, Washington, DC. U.S. Environmental Protection Agency (2009) . Assessment of the Impacts of Global Change on Reg ional U.S. Air Quality: A Synthesis of Climate Change Impacts on Ground- Level Ozone . An Interim Report of the U.S. EPA Global Change Research Program. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R–07/094.***E.O. 12866 Review – Revised Version – Do Not Cite, Quote, or Release During Review***

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3 - 11 U.S. Global Change Research Progr am ( USGCRP ) . Global Climate Change Impacts in the United States. Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson, (eds.). Cambridge University Press, 2009.