Summary and Assessment

GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS: UNDERSTANDING THE CONTRIBUTIONS TO INFECTIOUS DISEASE EMERGENCE

Humans have long recognized that climatic conditions influence the appearance and spread of epidemic diseases (NRC, 2001). Hippocrates’ observations of seasonal illnesses, in the fifth century B.C.E., formed the basis for his treatise on epidemics. Hippocratic medicine, which attempted to predict the course and outcome of an illness according to its symptoms, also considered winds, waters, and seasons as diagnostic factors. Ancient notions about the effects of weather and climate on disease remain in the medical and colloquial lexicon, in terms such as “cold” for rhinovirus infections; “malaria,” derived from the Latin for “bad air”; and the common complaint of feeling “under the weather.”

Today, evidence that the Earth’s climate is changing (IPCC, 2007b) is leading researchers to view the long-standing relationships between climate and disease from a global perspective. Increased atmospheric and surface temperatures are already contributing to the worldwide burden of disease and premature deaths, and are anticipated to influence the transmission dynamics and geographic distribution of malaria, dengue fever, tick-borne diseases, and diarrheal diseases such as cholera (IPCC, 2007a). Global warming is also accelerating the worldwide

The Forum’s role was limited to planning the workshop, and the workshop summary has been prepared by the workshop rapporteurs as a factual summary of what occurred at the workshop.



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Summary and Assessment GLOBAL CLIMATE CHANGE AND ExTREME WEATHER EVENTS: UNDERSTANDING THE CONTRIBUTIONS TO INFECTIOUS DISEASE EMERGENCE Humans have long recognized that climatic conditions influence the appear- ance and spread of epidemic diseases (NRC, 2001). Hippocrates’ observations of seasonal illnesses, in the fifth century B.C.E., formed the basis for his treatise on epidemics. Hippocratic medicine, which attempted to predict the course and outcome of an illness according to its symptoms, also considered winds, waters, and seasons as diagnostic factors. Ancient notions about the effects of weather and climate on disease remain in the medical and colloquial lexicon, in terms such as “cold” for rhinovirus infections; “malaria,” derived from the Latin for “bad air”; and the common complaint of feeling “under the weather.” Today, evidence that the Earth’s climate is changing (IPCC, 2007b) is leading researchers to view the long-standing relationships between climate and disease from a global perspective. Increased atmospheric and surface temperatures are already contributing to the worldwide burden of disease and premature deaths, and are anticipated to influence the transmission dynamics and geographic distri- bution of malaria, dengue fever, tick-borne diseases, and diarrheal diseases such as cholera (IPCC, 2007a). Global warming is also accelerating the worldwide The Forum’s role was limited to planning the workshop, and the workshop summary has been pre- pared by the workshop rapporteurs as a factual summary of what occurred at the workshop. 

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2 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS hydrological cycle, increasing the intensity, frequency, and duration of droughts; heavy precipitation events; and flooding (IPCC, 2007a). Such extreme weather events have been increasing (IPCC, 2007a) and have been linked to global warm- ing (Hoyos et al., 2006). These weather events may, in turn, contribute to and increase the risk for a wide range of vector- and non-vector-borne diseases in humans, plants, and animals (IPCC, 2007b). The projected health consequences of future climate change and extreme weather events are predominantly negative.1 The most severe impacts are expected to occur in low-income countries where adaptive capacity is weakest. Developed countries are also vulnerable to the health effects of weather extremes, as was demonstrated in 2003 when tens of thousands of Europeans died as a result of record-setting summer heat waves (Kovats and Haines, 2005). Climate change is expected to reinforce additional contributors to infectious disease emergence including global trade and transportation, land use, and human migration (IOM, 2003). The Forum on Microbial Threats of the Institute of Medicine (IOM) held a public workshop in Washington, DC, on December 4 and 5, 2007, to explore the anticipated direct and indirect effects of global climate change and extreme weather events on infectious diseases of humans, animals, and plants and the implications of these health impacts for global and national security. Through invited presentations and discussions, invited speakers considered a range of topics related to climate change and infectious diseases, including the ecological and environmental contexts of climate and infectious diseases; direct and indirect influences of extreme weather events and climate change on infectious diseases; environmental trends and their influence on the transmission and geographic range of vector- and non-vector-borne infectious diseases; opportunities and challenges for the surveillance, prediction, and early detection of climate-related outbreaks of infectious diseases; and the international policy implications of the potentially far-reaching impacts of climate change on infectious disease. Organization of the Workshop Summary This workshop summary report was prepared for the Forum membership in the name of the rapporteurs and includes a collection of individually-authored 1 In a personal communication on June 11, 2008, Diarmid Campbell-Lendrum (WHO) stated: “Some benefits undoubtedly exist, for some populations. But I don’t know of any papers in the health literature, WHO, or otherwise that specifically focus on reviewing the benefits separate from the damages. These are usually referred to in reviews that look at the health effects overall. The health chapter of the IPCC refers to both harms and benefits, and I think this would be the best citation, and source for other studies. In IPCC (2007a), Confalonieri et al. note that the most important benefits are likely to be reduced deaths in winter at high latitudes, increased food production in high latitudes (for moderate climate change), and disruption of transmission cycles of some infectious disease in some places (e.g., where it may become too hot or dry for malaria transmission in some locations).”

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 SUMMARY AND ASSESSMENT papers and commentary. Sections of the workshop summary not specifically attributed to an individual reflect the views of the rapporteurs and not those of the Forum on Microbial Threats, its sponsors, or the IOM. The contents of the unat- tributed sections are based on presentations and discussions at the workshop. The workshop summary is organized into chapters as a topic-by-topic description of the presentations and discussions that took place at the workshop. Its purpose is to present lessons from relevant experience, to delineate a range of pivotal issues and their respective problems, and to offer potential responses as discussed and described by workshop participants. Although this workshop summary provides an account of the individual presentations, it also reflects an important aspect of the Forum philosophy. The workshop functions as a dialogue among representatives from different sectors and allows them to present their beliefs about which areas may merit further attention. The reader should be aware, however, that the material presented here expresses the views and opinions of the individuals participating in the workshop and not the deliberations and conclusions of a formally constituted IOM study committee. These proceedings summarize only the statements of participants in the workshop and are not intended to be an exhaustive exploration of the subject matter or a representation of consensus evaluation. Workshop Context and Scope Encouraged by opening remarks from the Forum’s chair, David Relman, and Harvey Fineberg, President of the IOM, workshop presenters and discus- sants attempted to identify scientific questions that must be answered in order to discern—and, ultimately, to predict—the effects of a changing climate on specific infectious diseases, as well as the technical means to tackle these issues. At the same time, workshop participants grappled with an overarching question: What degree of scientific certainty that global climate change threatens human, animal, and plant health must be achieved before taking actions to mitigate these effects? The National Research Council (NRC) report Under the Weather: Climate, Ecosystems, and Infectious Diseases (2001) has served as both a springboard and a resource for many discussions, including this workshop. The meeting began with a keynote address by Donald Burke of the University of Pittsburgh, who chaired the interdisciplinary committee that produced that influential report (see Burke in Chapter 1). Its key findings, summarized in Box SA-1, reflect consid- erable scientific uncertainty regarding the causal relationship between global climate change and infectious disease emergence.2 2 Emerging infectious diseases are caused by pathogens that (1) have increased in incidence, geo- graphical, or host range; (2) have altered capabilities for pathogenesis; (3) have newly evolved; or (4) have been discovered or newly recognized (Anderson et al., 2004; Daszak et al., 2000; IOM, 1992).

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 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS BOX SA-1 Under the Weather Key Findings: Linkages Between Climate and Infectious Diseases • Weather fluctuations and seasonal-to-interannual climate variability influence many infectious diseases. • Observational and modeling studies must be interpreted cautiously. • The potential disease impacts of global climate change remain highly uncertain. • Climate change may affect the evolution and emergence of infectious diseases. • There are potential pitfalls in extrapolating climate and disease relationships from one spatial or temporal scale to another. • Recent technological advances will aid efforts to improve modeling of infec- tious disease epidemiology. SOURCE: NRC (2001). This nuanced assessment has endured, as demonstrated in the 2007 report of Working Group II of the Intergovernmental Panel on Climate Change (IPCC), whose members studied the influence of climate change3 on biological and social systems (IPCC, 2007a). The report states with “very high confidence” that “cli- mate change currently contributes to the global burden of disease and premature deaths,” but notes that “at this early stage the effects are small but are projected to progressively increase in all countries and regions.” Physical Evidence of Climate Change There is little doubt that Earth’s climate is changing as a result of human activities. The IPCC’s Working Group I, which assessed the physical science of climate change, concluded that the “warming of the climate system is unequivo- cal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global aver- age sea level” and that “most of the observed increase in global average tempera- tures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC, 2007b). A more detailed discussion of these findings appears in Appendix SA-1 (see page 43), “A Brief History of Climate Change,” and in Chapter 1. 3 Climate change in IPCC usage, and in this document as well, refers to any change in climate over time, whether due to natural variability or as a result of human activity.

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 SUMMARY AND ASSESSMENT Several workshop participants remarked on the IPCC’s conclusions and called attention to the following general observations suggestive of the broad, profound, and rapidly accelerating impacts of climate change on Earth’s physi- cal systems: • Oceans as heat sinks: Energy from global warming has been absorbed almost entirely by ocean waters, and relatively little has contributed to the melt- ing of glacial ice or increases in air temperatures (Barnett et al., 2005; Levitus et al., 2005). To date, the thermal expansion of seawater accounts for about half of the observed rise in sea level. As sea levels rise, coastal flooding occurs more frequently and groundwater becomes increasingly saline. • Warming at high latitudes: Warming is occurring fastest in boreal and arctic regions,4 where its effects are amplified by the melting of snow, ice, and tundra (which also releases methane, a greenhouse gas), according to speaker Paul Epstein of the Harvard Medical School. Measurements by speaker Compton Tucker of the National Aeronautics and Space Administration (NASA) reveal that Greenland (which he described as a “canary for climate change”) is melting at an accelerating pace that currently results in a net loss of approximately 160 km 3 of ice per year (see Tucker in Chapter 3). • Heat waves: Epstein observed that climate change is not only associated with increases in the extent, breadth, intensity, and frequency of heat waves, but also with disproportionately elevated nighttime temperatures, which have increased twice as fast as average ambient temperatures since 1970. He also noted that as warming increases the levels of atmospheric water vapor, heat waves are more likely to be accompanied by increased humidity (IPCC, 2007b; see also Milly et al., 2005). • Dwindling freshwater supplies: Warmer temperatures mean less water stored in glaciers and snow cover, which yield freshwater for approximately one-sixth of the world’s population (IPCC, 2007a), according to presenter Sir Andrew Haines of the London School of Hygiene and Tropical Medicine. By 2050, he said, annual river runoffs are predicted to decrease by 10 to 30 percent in midlatitude dry regions and in the dry tropics (Milly et al., 2005). • Hydrological extremes: Warming of the global climate system acceler- ates the hydrological cycle, producing more droughts, floods, and other extreme weather events. Warming-induced evaporation causes drought in some places, while higher atmospheric water content leads to more intense downpours else- where (Karl and Trenberth, 2003). Epstein remarked that the confluence of trends toward increased interannual variability in precipitation (IPCC, 2001, 2007b), heavier precipitation events (Groisman et al., 2004), and more winter precipitation falling as rain rather than snow (Frederick and Gleick, 1999; Gleick, 2004; Levin et al., 2002) reflects the 4 North and South Poles.

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 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS overall increase in seasonal (and, apparently, day-to-day) hydrological variabil- ity. He also noted that successive droughts punctuated by heavy rains not only favor flooding, but may also destabilize ecosystems, creating conditions that may be associated with clusters of mosquito-, rodent-, and water-borne disease outbreaks.5 • Higher winds: Circumpolar westerly winds are accelerating, particularly in the Southern Hemisphere (Gillett and Thompson, 2003; IPCC, 2007a), an effect Epstein described as a key sign of climatic instability.6 Moreover, he said, as temperatures rise and pressure gradients build, winds can be expected to increase in intensity, generating stronger windstorms and altering the movement of weather fronts. In June 2008, the U.S. Climate Change Science Program and the Subcom- mittee on Global Change Research released a report entitled Weather and Cli- mate Extremes in a Changing Climate. While the IPCC (2007) report looked at the global effects of climate change on biological and social systems, this report focuses on the effects of climate change in North America, Hawaii, the Caribbean, and the U.S. Pacific Islands. Table SA-1 illustrates observed climate phenomena in the last 50 years and projects the likelihood of continued changes in North America. These phenomena include warmer days and nights, increased precipitation, more intense hurricanes, and larger areas affected by drought. Over the last two decades, hydrometeorological disasters (e.g., hurricanes, droughts, floods) have affected a steadily increasing number of people living in vulnerable areas, most of them in developing countries, as shown in Figure SA-1. This development might be more accurately described as “global weird- ing,” Burke said, in order to capture both the severity and the unpredictability of weather events spawned by global warming. As discussed in subsequent sections of this summary and in Chapter 1, extreme weather conditions increase the risk of transmission for a variety of infectious diseases, including diarrheal diseases, vector-borne diseases, and respiratory infections. Following a weather disaster such as a hurricane, affected areas must often cope with multiple infectious dis- ease outbreaks. Coincident Changes in Climate and Infectious Diseases There are no appropriate, independent controls for the study of global climate change on Earth, Epstein observed. A wide range of methodologies must be har- 5 In some cases, however, flooding may be associated with the destruction of vector breeding sites. 6 Findings indicative of climate instability include (1) increasing rates of change, (2) wider fluctua- tions from norms, and (3) the appearance of major outliers (several standard deviations from the norm; Epstein and McCarthy, 2004).

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7 SUMMARY AND ASSESSMENT TABLE SA-1 Observed Changes in North American Extreme Events, Assessment of Human Influence for the Observed Changes, and Likelihood That the Changes Will Continue Through the Twenty-first Centurya Likelihood of Phenomenon Where and when Linkage of human continued future and direction these changes occurred in activity to observed changes in this of change past 50 years changes century Very likelyd Warmer and fewer Over most land areas, the Likely warmer cold days and nights last 10 years had lower extreme cold days numbers of severe cold and nights and fewer frostsb snaps than any other 10- year period Very likelyd Hotter and more frequent Over most of North Likely for warmer nightsb hot days and nights America Very likelyd More frequent heat Over most land areas, Likely for certain waves and warm spells most pronounced over aspects, e.g., night- northwestern two-thirds of time temperatures; North America and linkage to record high annual temperatureb Very likelyd More frequent and Over many areas Linked indirectly intense heavy downpours through increased and higher proportion water vapor, a critical of total rainfall in heavy factor for heavy precipitation eventsc precipitation events Increases in area affected No overall average change Likely, southwest Likely in USA.c Evidence by drought for North America, but Southwest USA, regional changes are that 1930s and parts of Mexico, and Carribeand evident 1950s droughts were linked to natural patterns of sea surface temperature variability Likelyd More intense hurricanes Substantial increase in Linked indirectly Atlantic since 1970; through increasing sea likely increase in Atlantic surface temperature, since 1950s; increasing a critical factor for intense hurricanes;e a tendency in W. Pacific and decreasing tendency in confident assessment requires further studyc E. Pacific (Mexico West Coast) since 1980e aBased on frequently used family of IPCC emission scenarios. bBased on formal attribution studies and expert judgment. cBased on expert judgment. dBased on model projections and expert judgment. eAs measured by the Power Dissipation Index (which combines storm intensity, duration, and frequency). SOURCE: U.S. Climate Change Science Program and the Subcommittee on Global Change Research (2008).

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 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS Developing countries High-income OECD, Central and Eastern Europe, and the CIS 250 200 150 100 50 0 1975–79 1980–84 1985–89 1990–94 1995–99 2000–04 FIGURE SA-1 People affected by hydrometeorological disaster (millions per year). SOURCE: Reproduced from United Nations Development Programme (2007) with per- mission of Palgrave Macmillan. Figure SA-1, replaced with vector-editable version from source nessed, therefore, in order to assess changes in biological variables—including the geographic range and incidence of diseases—in relation to changes in tem- perature and precipitation (see Chapter 1). Information obtained from a variety of monitoring and mapping techniques can be integrated into geographic infor- mation systems (GISs) and used to identify and compare physical and biological phenomena. By enabling the overlay of multiple sets of data, GISs also provide contributions to descriptive and mathematical models that may be used to project the biological impacts of various climate change scenarios. Additional methods are used to analyze data gathered across scientific disciplines in order to reveal patterns and emerging trends associated with climate change, calculate rates of change (i.e., in the geographic range, prevalence, and incidence of infectious diseases), and compare these observations with predicted outcomes. Many of the methodologies used to study the effects of climate change yield correlations, rather than proof of causation, Epstein acknowledged, but he argued that when observational data from multiple sources (1) match model projections,

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 SUMMARY AND ASSESSMENT (2) are consistent with each other, and (3) can be explained by plausible biologi- cal mechanisms, the preponderance of the evidence warrants further attention and exploration. Moreover, he added, models could be used to test such associations and their apparent underlying mechanisms (see Chapter 1). In particular, Epstein identified three outcome variables as central to under- standing the effect of climate change on the distribution of infectious diseases: shifts in altitude (and latitude), changes in seasonality, and responses to increased weather variability. Shifts in altitude Many animal and plant species are adapted to specific habitats that occupy a narrow range along altitudinal and latitudinal climatic gradients. 7 Increasing temperatures not only melt alpine glaciers and drive the upward migra- tion of plant communities, but also enable insects and other species that serve as infectious disease vectors to occupy higher altitudes (Epstein et al., 1998). 8 Such changes in conditions—which are conducive to changes in the ranges of disease agents and vectors—are occurring at high-altitude locations across the globe: in the Andes, the Sierra Nevada, the East African highlands, the European Alps, and the mountainous regions of India, Nepal, and Papua New Guinea, Epstein observed. Seasonal shifts Climatic warming is expected to lengthen seasonal activity peri- ods for mosquitoes and other insect vectors, thereby increasing opportunities for exposure to infectious diseases such as malaria (Tanser et al., 2003; van Lieshout et al., 2004). Ecological opportunists—including insects and rodents that serve as vectors of, and reservoirs for, infectious diseases—tend to proliferate rapidly in disturbed environments, while large predator species (infectious disease hosts) suf- fer under unstable environmental conditions, Epstein said. Responses to increased weather variability Increased climate variability, along with habitat fragmentation and pollution, is likely to alter predator-prey relation- ships, which in turn influence infectious disease transmission dynamics. Such disequilibrium is thought to have precipitated the 1993 outbreak of a rodent-borne infection, hantavirus pulmonary syndrome, in the Four Corners region of the south- western United States. That year, early, heavy rains ended an intense drought (dur- ing which predator populations declined) and provided new food for rodents, whose populations then expanded rapidly (Calisher et al., 2005; Patz et al., 1996). 7 Plant and animal species first adapt to temperature changes by shifting their elevational ranges. A 1 km change in altitude is estimated to correspond to a geographic shift of 600 km north or south (Peters and Lovejoy, 1994). Highlands are considered sentinel regions for monitoring the biological response to global climate change. 8While some vectors may already be present at higher altitudes, higher temperatures may shorten the extrinsic incubation period, allowing the vector to transmit disease.

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0 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS While it is anticipated that climate change will influence infectious disease emergence, several workshop participants emphasized that direct causal connec- tions have yet to be established between climate change and infectious diseases, and that accurate predictions of infectious disease behavior cannot yet be made on the basis of climate projections alone. Climate and Health “Climate change will affect the health of humans as well as the ecosystems and species on which we depend, and . . . these health impacts will have economic consequences,” predicts a recent report published by the Center for Health and the Global Environment (2005), edited by Epstein and Evan Mills (see Chapter 1 for the executive summary of this report, Climate Change Futures: Health, Ecologi- cal and Economic Dimensions). The report highlights a broad range of known and anticipated health consequences of climate change for humans, animals, and plants. In addition to influencing the location and frequency of infectious disease emergence and outbreaks, these effects include increased pest damage of crop plants, which in turn could contribute to human malnutrition; greater concentra- tions of pollen and fungi in the air, raising the risk of allergic symptoms and asthma; and higher rates of injury and death due to weather disasters and fires. Indeed, as Epstein (2005) has concluded, “it would appear that we may be under- estimating the breadth of biologic responses to changes in climate.” Figure SA-2 illustrates the multiple pathways by which variations in cli- mate affect the health of humans, animals, and plants. Direct influences include long-term regional changes in average temperature and precipitation, as well as extreme weather events such as floods, droughts, or violent storms. Climate change may also exert health effects indirectly, by altering ecosystems in ways that, for example, affect the geographic distribution or transmission dynamics of infectious diseases. Direct and Indirect Effects of Climate on Infectious Diseases Climate exerts both direct and indirect influences on the transmission and geographic distribution of infectious diseases, such as those shown in Table SA-2 (NRC, 2001). Direct effects of climate on infectious disease occur through the following mechanisms: • Pathogen replication rate. This is particularly true of vector-borne diseases of warm-blooded animals, due to the exposure of pathogens to ambient weather conditions for part of their life cycle. • Pathogen dissemination. This occurs when floods contaminate drinking water reservoirs, resulting in diarrheal diseases, and also when dry winds distrib- ute soil-borne pathogens.

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Adverse Health Effects Heat-Related Illnesses and Deaths Extreme Weather Related Health Effects Changes in Intermediate Factors Regional and Local Air Pollution Concentration Air Pollution Weather Change and Distribution Related Health Effects Natural and Climate Variability Extreme Weather Human Influences and Change Pollen Production Allergic Diseases Temperature on Climate Precipitation Infectious Diseases Water- and Microbial Contamination Food-Borne Diseases and Transmission Vector- and Rodent-Borne Diseases Crop Yield Malnutrition Mitigation Policies Storm Surge-Related Coastal Flooding Drowning and Injuries Change in Health Problems of Sea Level Coastal Aquifer Salinity Displaced Populations Moderating Influences and Adaptation Measures Mitigation Policies for Reduction Moderating Influences Adaptation Measures of Greenhouse Gas Emissions Population Density and Growth Vaccination Programs Energy Efficiency Level of Technological Development Disease Surveillance Use of Renewable Energy Sources Standard of Living and Local Environmental Condition Protective Technologies Forest Preservation Preexisting Health Status Weather Forecasting and Warning Systems Quality and Access to Health Care Emergency Management and Disaster Preparedness Public Health Infrastructure Public Health Education and Prevention Legislation and Administration FIGURE SA-2 Potential health effects of climate variability and change. SOURCE: Reprinted with permission from the American Medical Association from Haines and Patz (2004). Copyright 2004. All rights reserved; adapted from Patz et al. (2000). 

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 SUMMARY AND ASSESSMENT BOX SA-3 Under the Weather Recommendations for Future Research and Surveillance • Research on the linkages between climate and infectious diseases must be strengthened. • Further development of disease transmission models is needed to assess the risks posed by climatic and ecological changes. • Epidemiological surveillance programs should be strengthened. • Observational, experimental, and modeling activities are all highly interdepen- dent and must progress in a coordinated fashion. • Research on climate and infectious disease linkages inherently requires inter- disciplinary collaborations. SOURCE: NRC (2001). APPENDIx SA-1 A BRIEF HISTORY OF CLIMATE CHANGE Long-Term Trends As illustrated in Figure SA-16, human history spans several periods of cli- matic upheaval (WHO et al., 2003). However, the warmth of the last half-century is unusual; indeed, evidence suggests that the last time the polar regions remained significantly warmer than they are today—approximately 125,000 years ago— reductions in polar ice volume caused global sea levels to rise by 4 to 6 meters. Recent Changes Over the last century, global average temperatures and sea levels have risen significantly, while snow cover in the Northern Hemisphere has declined (see Fig- ure SA-17; National Geographic Society, 2007). The total temperature increase from 1850-1899 to 2001-2005, estimated at 0.76°C (0.57°C to 0.95°C), occurred during a warming trend that appears to be gaining momentum. The rate of warm- ing for the last 50 years was double that during the previous half-century, and 11 of the last 12 years (1995-2006) rank among the 12 warmest years in the instru- mental record of global surface temperature (since 1850). Over the last 50 years, cold days, cold nights, and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent. Measurements conducted since 1961 show that the average temperature of the global ocean has increased to depths of at least 3,000 meters and that oceans have absorbed more than 80 percent of the heat added to the climate system.

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 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS 5 4 Average temperature over past 10 000 years = 15°C IPCC (2001) forecast: +2–3°C, with band 3 of uncertainty 2 Mesopotamia Temperature change (°C) flourishes Agriculture 1 emerges Vikings in Greenland 0 Holocene Medieval Optimum 1940 21st Warm –1 Little ice age century: in Europe very rapid (15th–18th rise –2 centuries) End of –3 last ice age –4 Younger Dryas –5 20 000 10 000 2000 1000 300 100 Now +100 Number of years before present (quasi-log scale) FIGURE SA-16 Variation in Earth’s average surface temperature over the past 20,000 years. SOURCE: Reprinted from WHO et al. (2003) with permission from the World Health Organization. Copyright 2003. Figure SA-16 replaced with download from source, ALL type is now vector Such warming causes seawater to expand, contributing to sea level rise, as have widespread decreases in glaciers and ice caps. Global average sea level rose at an average rate of 1.8 mm per year between 1961 and 2003 and at a rate of about 3.1 mm per year between 1993 and 2003. Current estimates indicate that sea levels rose 0.17 m over the course of the twentieth century (see Figure SA-18; IPCC, 2007). Present Effects and Future Projections A warmer global climate system accelerates the hydrological cycle, increas- ing the likelihood of extreme weather phenomena such as droughts, heavy pre- cipitation, heat waves, hurricanes, typhoons, and cyclones (see Figure SA-19; National Geographic Society, 2007). More intense and longer droughts, which have been observed over wider areas since the 1970s and particularly in the trop- ics and subtropics, have been associated with higher global temperatures, but also

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FIGURE SA-17 The Arctic is experiencing the fastest rate of warming as its reflective covering of ice and snow shrinks. In the midlatitudes, there are now fewer cold nights; heat waves are more common. The Indian Ocean and the western Pacific Ocean are warmer than at any point in the last 11,500 years. Against the trend: Pockets of the oceans are cooled by deepwater upwellings. Ozone loss over the South Pole may SA-17 color have cooled parts of Antarctica. SOURCE: Reprinted from National Geographic Society (2007) with permission from the National Geographic Society.  Broadside bitmapped

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 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS FIGURE SA-18 Observed changes in (A) global average surface temperature; (B) global average sea level rise from tide gauge (blue) and satellite (red) data; and (C) Northern SA-18 color Hemisphere snow cover for March-April. All changes are relative to corresponding aver- Bitmapped ages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (A and B) and from the time series (C). SOURCE: Figure SPM.3 in IPCC (2007).

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FIGURE SA-19 Drought is seizing more territory in the wake of mounting temperatures. Drying trends in the last 30 years are evident in the rain forests of Africa and South America and in already dry regions such as southern Europe and western North America. In wet areas, precipitation increasingly arrives in heavy downpours, raising theSA-19flooding. Winter rain is replacing snow, an ominous development for risk of Color hundreds of millions of people who depend on spring snowmelt for their water Bitmappedsupply. 7 SOURCE: Reprinted from National Geographic Society (2007) with permission from the National Geographic Society. Broadside

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 GLOBAL CLIMATE CHANGE AND EXTREME WEATHER EVENTS with changes in wind patterns and decreases in snowpack and snow cover. Periods of heavy precipitation have occurred with greater frequency over most land areas in parallel with increases in atmospheric water vapor. Over the next two decades, the Earth is expected to warm by an additional 0.2°C. Even if the concentrations of all greenhouse gases and aerosols (both of which cause the atmosphere to trap heat) could be kept the same levels as in 2000, warming would still be expected to proceed at about half the present rate. Contin- ued greenhouse gas emissions at or above current rates are very likely to induce changes in the global climate system during the twenty-first century of even greater magnitude than has been observed during the late twentieth century. REFERENCES Summary and Assessment References Anderson, P. K., A. A. Cunningham, N. G. Patel, F. J. Morales, P. R. Epstein, and P. Daszak. 2004. Emerging infectious diseases of plants: pathogen pollution, climate change and agrotechnology drivers. Trends in Ecology and Evolution 19(10):535-544. Anyamba, A., J. P. Chretien, J. Small, C. J. Tucker, and K. J. Linthicum. 2006. Developing global climate anomalies suggest potential disease risks for 2006-2007. International Journal of Health Geographics 5:60. Barnett, T. P., D. W. Pierce, K. M. AchutaRao, P. J. Gleckler, B. D. Santer, J. M. Gregory, and W. M. Washington. 2005. Penetration of human-induced warming into the world’s oceans. Sci- ence 309(5732):284-287. BBC News. 2007. The rise of bluetongue disease. BBC News, http://news.bbc.co.uk/2/hi/uk_ news/7009288.stm (accessed June 20, 2008). Borgerson, S. G. 2008. Arctic meltdown: the economic and security implications of global warming. Foreign Affairs 87(2):63-77. Calisher, C. H., J. J. Root, J. N. Mills, J. E. Rowe, S. A. Reeder, E. S. Jentes, K. Wagoner, and B. J. Beaty. 2005. Epizootiology of Sin Nombre and El Moro Canyon hantaviruses, southeastern Colorado, 1995-2000. Journal of Wildlife Diseases 41(1):1-11. CDC (Centers for Disease Control and Prevention). 2004. Giardiasis fact sheet, http://www.cdc. gov/ncidod/dpd/parasites/giardiasis/factsht_giardia.htm#child_diagnosed (accessed March 17, 2008). ———. 2005. Cholera: frequently asked questions, http://www.cdc.gov/ncidod/dbmd/diseaseinfo/ cholera_g.htm (accessed March 17, 2008). ———. 2007a. Cryptosporidium infection fact sheet, http://www.cdc.gov/ncidod/dpd/parasites/ cryptosporidiosis/factsht_cryptosporidiosis.htm (accessed March 17, 2008). ———. 2007b. Rift Valley fever outbreak—Kenya, November 2006-January 2007. Morbidity and Mortality Weekly Report 56(4):73-76. Center for Health and the Global Environment. 2005. Climate change futures: health, ecological and economic dimensions. Cambridge, MA: Harvard Medical School. CGIAR (Consultative Group for International Agricultural Research). 2008. http://www.cgiar.org/ (accessed March 16, 2008). Chretien, J. P., A. Anyamba, S. A. Bedno, R. F. Breiman, R. Sang, K. Sergon, A. M. Powers, C. O. Onyango, J. Small, C. J. Tucker, and K. J. Linthicum. 2007. Drought-associated chi- kungunya emergence along coastal East Africa. American Journal of Tropical Medicine and Hygiene 76(3):405-407.

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