REPORT OF THE COUNCIL ON SCIENCE AND PUBLIC HEALTH

 

CSAPH Report 3-I-08

 

 

 

Resolution 442, introduced by the Section on Medical Schools and referred at the 2007 Annual Meeting, asks:

 

That our American Medical Association (AMA) work in coalition with members of the Federation and other health professional organizations to create a report due back at the 2008 Annual Meeting updating AMA policy on climate change so it is consistent with current science; and recommending how the AMA should work in coalition with other health professional organizations to help prevent or reduce climate changes that adversely affect health, and to help prepare current and future U.S. Physicians for climate change and its health effects.

 

Resolution 430, introduced by the American Thoracic Society and referred at the 2008 Annual Meeting, asks:

 

That our AMA: (1) endorse the findings of the 4th Intergovernmental Panel on Climate Change; (2) support research to explore the human health effects of climate change; (3) support state, federal and international policy coordination to develop adaptive strategies to respond to the predicted human health effects of climate change; and (4) encourage Congress and the President to adopt national and international policies to reduce the emissions of greenhouse gases.

 

Current AMA policies on climate change support increased atmospheric modeling research to reduce confusion or uncertainty in climate change predictions, and energy policies that support natural resource integration and efficient energy production. Our AMA also endorses awareness of the potential role of nuclear power for electricity production, pollution reduction efforts, and programs that reduce the health impacts of, as well as maintaining a global perspective on, environmental problems (Policies H-135.972, H-135.977, and H-135.973 [AMA Policy Database]; see also Appendix 1).

 

This report reviews the current scientific information on climate change and discusses some predicted health effects facing various populations as a result of global climate change and modified weather patterns. New policy recommendations for our AMA are also presented.

 

Significant advances have occurred in the understanding of global climate change, and a large volume of published literature on this topic has appeared, particularly in the last half-century.¹ Increased scientific knowledge and improved methodology account for a more thorough portrayal of climate changes and the predicted impacts of such changes.

 

Monitoring of the climate system and weather patterns has been ongoing since the early 19^th century. Most early monitoring systems were individual efforts to identify patterns and trends in specific weather situations, or one variable of a weather system, such as precipitation or air temperature. Several scientists have attempted to produce accurate time series reflecting weather changes over time. In the 1880s Koppen studied the Earth’s annual mean temperature by compiling data from 100 stations located across major latitude belts.² Subsequently, others expanded the use of weather stations to create global time series. In addition, scientists continued to adjust data sets for homogeneity through more advanced statistical designs. These adjustments help to account for differences in instrumentation sensitivity, station changes, and structural environmental changes such as urbanization.³ 

 

Although these individual efforts produced useful data, a more global approach to climate monitoring was clearly needed. Historically, the International Meteorological Association, formed in response to a paper published in 1872, “Suggestions on a Uniform System of Meteorological Observations,” was eventually succeeded by the World Meteorological Organization, which is still in existence. Although over time the number of weather monitoring stations has increased, and approaches used to study changes in weather and temperature patterns have changed, data generated from time series analyses are generally consistent (see The Climate System sectionbelow).⁴

Study of the climate and climate change continued as an international effort in the late 20^th century as groups formed in the effort to decisively confront the effects of humans on the climate system. In 1985 the United Nations Environment Programme (UNEP), the World Meteorological Organization (WMO), and the International Council for Science (ICSU) held a joint conference to study the role of greenhouse gases and their relationship to climate change. Based on a perceived need for more information, the Advisory Group on Greenhouse Gases (AGGG) was created to study this issue. Two years later, the need for additional data on climate change was raised at the 10th congress of the WMO, prompting the WMO executive council, in conjunction with the UNEP, to form a another committee, this one tasked with providing an “objective, balanced, and internationally coordinated scientific assessment of the understanding of the effects of increasing concentrations of greenhouse gases on the Earth’s climate and on ways in which these changes may impact socio-economic problems.” The IPCC was therefore established in 1990, at the executive council meeting of the WMO.⁵

The IPCC is a large international body and has three working groups. The IPCC does not conduct primary research, rather it builds consensus from the collective efforts of scientists worldwide. Working group I focuses on current scientific data, working group II focuses on the environmental and socioeconomic impact of climate change, and working group III is charged with formulating response strategies to these impacts. Each working group maintains a core membership from 13 to 17 countries, with participation from additional sources. A bureau, comprised of the IPCC chair, three IPCC vice chairs, and the co-chairs and vice chairs from each of the working groups oversees all IPCC activity. Currently, the bureau has 27 members, including two co-chairs of a new IPCC Task Force on National Greenhouse Gas Inventories.⁶  To date the IPCC has released four assessment reports on global climate change, as well as several special reports.

 

Climate is a complex and dynamic process influenced by many factors. By definition, climate is the mean and variability of temperature, wind, and precipitation over a long period of time. Periods of 30 years are used most frequently to assess climate variability.⁷ This is in contrast to “weather,” which is used to describe changes in atmospheric conditions (temperature, wind and precipitation) over brief periods of time, such as days or weeks. Changes in climate, such as warming, alter patterns of weather. The climate system is influenced by both internal and external factors, referred to as “forcings.” Internal forcings include volcanic activity and changes in solar radiation, whereas external forcings include human activities affecting climate patterns.

 

Solar radiation is the driving force behind the climate system. Several factors can affect the amount of solar radiation in the atmosphere at any given time. Changes in the orbital patterns of the Earth or changes in the Sun will affect how much radiation actually reaches the planet. In addition, once solar radiation reaches the atmosphere, several factors affect how much is reflected, such as the percentage of cloud cover, the concentration and type of particles in the atmosphere, the amount of vegetation in a region, and the extent of ice and snow cover. The climate hinges on an energy balance that must be maintained. Energy, in the form of solar radiation, is absorbed by the Earth if not reflected back, and thus the Earth must radiate energy in the same proportion that it is absorbed. Complex feedback loops affect the atmospheric circulation (driven by heat and the oceans), and can either amplify or diminish the effects of forcings.⁴

 

The Earth has a natural greenhouse effect that is the result of the thermal radiation emitted by land and air being absorbed by the atmosphere and radiated back to Earth. Without this phenomenon, the Earth would be substantially colder and uninhabitable for humans. The greenhouse effect can be intensified by increases in gases that collect more heat, and to a lesser extent by changes in topography. Gases that trap heat in the atmosphere are routinely called greenhouse gases and are produced in varying quantities from different sources. The most prevalent greenhouse gas is water vapor, followed by carbon dioxide, methane, nitrogen oxide, and ozone and fluorinated gases such as halocarbons, perfluorocarbons, and sulfur hexafluoride. 

 

Although many of these gases emanate from natural sources, some are increasing in concentration as a result of human activity.⁸ The interaction of these gases with aerosols and other climate forcings is of continuing interest and the subject of climate modeling. Increasing greenhouse gas concentrations over humid regions of the globe, such as equatorial regions, has a lesser impact than increasing concentrations over colder or drier climates, such as in the northern latitudes. For every 1°C the atmosphere warms up, it can hold 7% more water vapor. As the air is usually highly saturated with water vapor in equatorial regions, the incremental addition of more CO_2, has considerably less impact.  However when water vapor is increased over a drier region, more upward infrared radiation is trapped, increasing the warming effect.⁴

 

 

Current estimates of the rate, type, and sources of climate change emanate from models. Because the climate system is complex and interdependent on many different forces, scenarios and modeling of current patterns of global climate change remain difficult to assess. Models contain different assumptions and variables, with the intent to accurately predict global climate temperature change (with accuracy defined as how close to a measured or calculated quantity the true value is). “Fingerprint” studies, on the other hand, are defined as those in which data (observations) match model projections, with model inputs including the forcing factors of greenhouse and other trace gases. When models are compared with one another, their relative precision (the degree to which repeated calculations show the same or similar results) may be apparent. As it is impossible to create an Earth-scale scenario to replicate findings, these models are by definition imprecise; however, they can still yield accurate predictions.

 

Models used to predict climate change have evolved over time to include additional variables, resulting in modified projections.^8,9   Many assumptions built into these models are based on paleoclimatic data, including ice core samples and tree ring measurements.   Because of limits in these assumptions, the initial IPCC model predicted a very wide range of potential increases in global temperature. Subsequent assessments incorporated more advanced modeling that resulted in narrower predicted values of atmospheric climate change. Accordingly, the first IPCC assessment report estimated yearly global average surface temperatures (1990-2005) that were higher than the subsequent estimates in the second and third assessment reports. However, all IPCC assessment reports have consistently predicted increases in global surface temperature. 

 

Additional improvements have been made in climate modeling methodology since the release of the IPCC’s Third Assessment Report (TAR).   Atmosphere-ocean general circulation models (AOGCMs) are generally well regarded for their ability to predict climate changes at the continental and global level and are the models primarily used to assess climate patterns. Nevertheless, challenges remain for assessing the validity of even the most complete AOGCMs, based on the relative degree of confidence (which is not uniform) for all variables. For example, precipitation values have not been as precisely projected as anticipated, and overall rainfall does not always indicate the shifts in the timing and intensity of precipitation. In addition, some biases remain, especially in simulation of the southern oceans and in some control situations. Additionally, simulation of the Madden-Julian Oscillation (an equatorial traveling pattern of anomalous rainfall that is planetary in scale) is not complete.

 

The Fourth Assessment Report (AR4) also notes that some models have only begun to incorporate more advanced carbon cycle measures as a variable (eg, permafrost, deforestation, oceans). The short- and long-term uptake and environmental storage mechanisms of carbon are better understood but remain difficult to incorporate. Because carbon has a latency period both for its uptake and its release within the environment, the inclusion of carbon cycle measures in future models will continue to be important.

 

Modeling has undergone increased scrutiny, testing, and evaluation in order to generate the most accurate models possible, containing the fewest fundamental errors. Simulations (except as noted above) have improved, and additional processes or variables have been added to various models to improve precision. With respect to the rigor of model evaluation, the IPCC working group I notes:

 

Eighteen modeling groups performed a set of coordinated, standard experiments, and the resulting model output, analyzed by hundreds of researchers worldwide, forms the basis for much of the current IPCC assessment of model results.  The benefits of coordinated model intercomparison include increased communication among modeling groups, more rapid identification and correction of errors, the creation of standardized benchmark calculations and a more complete and systematic record of modeling progress.⁸

 

Recognizing the limits of current models and their ongoing refinement, the overwhelming majority of the scientific community has accepted the IPCC projections and supports them as outlined in the AR4. The IPCC does have a vocal minority of critics who maintain that the IPCC, as a scientific body and in its processes, is flawed.^10,15 While acknowledging that the IPCC process has criticisms, our AMA believes that the IPCC as a scientific body is sound.

 

Due to the limitations of climate modeling, there are several scenarios of how quickly and to what extent the effects will manifest. However, testimony from the National Oceanic and Atmospheric Association (NOAA), Centers for Disease Control and Prevention (CDC), EPA, National Climatic Data Center, Pew Research Center, WHO, and other leading scientific organizations support and cite the IPCC AR4 projections.^16,21 In addition, the majority of scientific studies cite the AR4 projections, including the most recent analysis published by the US Climate Change Science Program.^22,23Accordingly, the IPCC projections are viewed as the most current and accurate by many in the scientific, medical, and public health communities.

 

Overall, the years 1995 to 2006 rank as the warmest in the instrumental record of global surface temperature since 1850. The synthesis report from the AR4 states:

 

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level. Sea level has risen at an average rate of 1.8 mm/year (1.3-2.3) from 1961 and at an even faster [pace] since 1993, at a rate of 3.1 mm/year (2.4-3.8). Arctic sea ice has decreased by 2.7% (2.1-3.3) per decade, and both glacial and snow cover has decreased in both hemispheres, according to satellite data.²²

 

The IPCC report projects that without intervention, global greenhouse gas emissions will continue to increase, as will the rate of warming. Estimates place the rate of climate change for the 21^st century above that which was observed in the 20^th century if greenhouse gas emissions continue at the current rate (or are increased). Currently, the special report on emission scenarios projects an increase of global greenhouse gas emissions of 25% to 90% between 2000 and 2030. This large range is a result of the use of multiple scenarios to model the impacts of different policies and variables on emissions.^22,24

 

A host of continuing environmental disruptions are also predicted. Warming will continue over land and in the northern latitudes. Snow cover area and sea ice will decrease and the permafrost regions will continue to thaw at deeper depths than previously seen, releasing methane, a potent greenhouse gas, which may significantly amplify atmospheric warming. Over the past half century (since 1957) the oceans have accumulated more than 22 times as much heat as has the atmosphere.²⁵ As surface and deep ocean temperatures are the main drivers of weather, it is highly likely (>90% probability) that there will be an increased frequency of hot extremes, heat waves, heavy precipitation, and especially heavy precipitation in the higher latitudes. An increase in tropical cyclone activity is possible (>60% chance), while an increase in wind speeds and durations (intensifying destructiveness) is projected by most models. Higher sea surface temperatures may also generate larger storms (with increased water vapor) and heavier precipitation.²⁶

 

Increasing rates of atmospheric CO₂ are also concerning. James Hansen, a noted physicist and director of NASA’s Goddard Institute for Space Studies, states that the safe level of atmospheric CO₂ is no more than 350 ppm, far less than previous estimates of 450 ppm. Current concentrations of atmospheric carbon are estimated to be between 385 to 390 ppm, and rising at a rate of about 2 ppm per year. Increasing atmospheric concentrations of carbon dioxide will lead to increased ocean acidification, reducing ocean pH by 0.14 to 0.35 units over the next century. This will affect marine shell-forming organisms and those dependent on them. Additionally, these increases will extend subtropical climate zones, causing glaciers to recede and diminishing fresh water supplies.²⁷

 

Irreversible effects are also predicted. Predictions of species extinction vary from 20% to 30% of those assessed to be at increased risk for extinction to 40% to 50% of assessed species, depending on the extent of global climate change.²²  Biodiversity is important for maintaining an adaptable and sustainable environment. The stability and prosperity of human society, along with the Earth's ecological balance, directly depend on the extent and status of biological diversity.

 

While some consider the IPCC to be somewhat “alarmist” in nature, there is also new scientific evidence that some of the IPCC’s predictions have actually underestimated potential climate changes. The sea level predictions of the IPCC have been confirmed by many scientists as inaccurate and as a result may have underestimated the actual rates of sea level rise. Originally, the IPCC predicted sea level rise due to thermal expansion of water and specifically did not consider sea level rise due to ice sheet melting, which is a nonlinear, chaotic, positive-feedback process and thus difficult to model. ²⁸ Because an increase in glacial melting has occurred at a higher than predicted rate as well, this will also increase sea level rise. The downstream effect of increased glacial melting may be a decrease in the overall reflectivity of the earth, which may trigger even more acute climate changes.

 

It is also possible that the range in which disease vectors (such as mosquitoes) exist may be underestimated when models using average temperatures are employed to support the projections. A rise in minimum temperatures accompanying climate change allows greater insect activity at night and over wintering. In both hemispheres the minimum temperature increased over the last half of the 20^th century.²⁹

The predicted climate changes in the AR4 present a catastrophic picture of global life if “business as usual” continues. Without mitigation or adaptive strategies, estimates of species extinction range from 20% to 50% and the sea level rise could displace up to 100 million people.^3,22

Climate does vary naturally. The earth was warmer in classical Greek and Roman times, cooled during the middle ages, and has been warming since the 16^th century based on glacial retreat data, but manmade activities have influenced the rate and extent of this process. Scientifically, changes in atmospheric concentrations of greenhouse gases and aerosols, land cover, and solar radiation can alter the balance of the climate system with either a warming or cooling effect. The question then becomes: To which component of this complex system can we attribute these changes? The IPCC synthesis report indicates that greenhouse gas emissions due to human activities have grown by 70% between 1970 and 2004.  Furthermore, atmospheric concentrations of CO₂, CH₄, and N₂O have increased since 1750 and now exceed preindustrial values based on ice core samples. Therefore, there is very high confidence (9 out of 10 chance of being correct) that the net effect of human activities since 1750 has been warming.²²

 

Each new assessment report builds on data from the previous report. The TAR attributed increases in average temperature to human activities, and the AR4 attributes additional developments to these activities. These include a portion of the sea level rise during the last half of the 20^th century, changes in wind patterns, increased temperatures for extreme hot nights, increased risk of heat waves, decreased temperatures for cold days and nights, the frequency of heavy precipitation events, and the size of the area affected by drought. These findings are the key fingerprint studies central to the conclusion that human activities are contributing to global warming. Most of these attributions are labeled as “very likely” or “likely.” In regard to heat waves, heavy precipitation events, and increased area of drought, the attribution is “more likely than not.” Probability-wise, these descriptors translate to a >90%, >66%, and >50% likelihood of event occurrence, respectively. Because 100% certainty about attributing a specific event to one source is lacking, the AR4 also notes:

 

More complete attribution of observed natural system responses to anthropogenic warming is currently prevented by the short time scales of many impact studies, greater natural climate variability at regional scales, contributions of non-climate factors, and limited spatial coverage of studies. ²²

 

Because attribution is less than 100% certain, some believe that the warming trends can be attributed to other sources, such as changes in solar radiation. However, the overwhelming majority of scientific evidence in the publishedliterature points to the conclusion that global climate change is occurring and the rate of this change is due to anthropogenic sources of global greenhouse gases.

The scope of contributory human activities is varied and goes beyond the traditional ideas of emissions and air pollution.  Current patterns of land, energy and water use will all determine how extensive global climate changes will be. Likewise, food production and distribution mechanisms are also contributing factors to this complex system.

 

The health effects attributable to warming of the global climate system have been detailed in many peer-reviewed journals and by association or organizational reports. Additionally, the AR4 lists 16 national health impact assessments that specifically outline the projected health problems for specific countries. The WHO, EPA, and Pew Center are only a few of the bodies that have undertaken comprehensive reports on climate and health. Consequently, this Council report does not attempt to recreate these extensive efforts. The following discussion focuses on the most commonly anticipated adverse health events and problems and provides relevant data (where possible) for those events that have been attributed to shifts in weather or extreme weather-related events.

 

The health effects attributable to climate change will vary in type, frequency, and intensity depending on many factors. While it is possible to outline some of the more obvious predicted adverse health effects, it is important to keep in mind that many of these will be enhanced or diminished by moderating influences or adaptation measures that can either enhance or diminish their severity. These measures and influences could include population density, pre-existing health status, public health infrastructure, disease surveillance, legislation, and so forth. The Figure below is a schematic diagram of this complex and dynamic system.

 

Most assessments of health and climate organize health issues categorically, as a direct effect, an indirect effect, or due to a social or economic disruption. Some health effects may fall into one or more categories. See Appendix 2 for an outline of some (but certainly not all) anticipated health concerns that could arise from global climate change.

 

The health effects most commonly predicted are related to heat waves, climate events related to changes in water levels (either extreme flooding or droughts), and increases in infectious and/or vector-borne diseases. Additional modeling has been conducted to estimate more of the downstream health effects of global climate change; these include changes in food yields and water supplies that could result in malnutrition and or dehydration. Projected problems with the food and water supplies also could cause increased migratory patterns, interpersonal conflicts, and societal pressures that might increase the extent of infectious disease, have mental health consequences, and provoke greater violence and injury.^31-32

 

Just as problems exist with climate modeling, several problems exist with estimating the health effects from climate change. Campbell-Lendrum describes a “gold standard” for assessing the impact of a specific event in relation to a health outcome:

 

Ideally, policymakers considering a particular decision should have quantitative estimates of the full range of effects on human health… based on standard epidemiologic methods… [that include measurement] of current and projected future exposure levels, consideration of the strength of evidence of an association between the risk factor and various health states, measurement of the relative risk of suffering the disease under alternative exposures, and adjustment for the effects of confounders or effect modifiers. ³³

 

Unfortunately, not all studies adhere to this framework. Many evaluate specific events (such as heat waves or floods) or report on trends in cities or regions. Many of the studies modeled to date focused on higher income countries, which may skew some of the findings. Access to services, infrastructure, and governmental response will vary greatly based on available resources. Thus, the modeled impact of a climate change event in a developing country may be more severe and have more unanticipated consequences compared with an event that occurs in a more developed nation. Nevertheless, the IPCC provides estimates on the likelihood of certain health problems based on the best available scientific evidence.

 

In July 2008, the US Climate Change Science Program released “Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems.” Similar to the IPCC report, this analysis predicts increased morbidity and mortality on a global scale over time as a result of climate change. Much of this is predicted to occur as a result of heat-exacerbated cardiovascular and pulmonary disease; increases in food- and waterborne pathogens; and catastrophic events, such as flooding, hurricanes, and wildfires. In addition, the report projects that the burden of morbidity and mortality will be unevenly distributed by region, and that “climate change is very likely to accentuate the disparities already evident in the American health care system.”²³

The following discussion focuses on the most commonly anticipated adverse health events and problems, and provides relevant data (where possible) for those events that have been attributed to shifts in weather or extreme weather-related events.

 

Some of the predicted health effects from global climate change are expected to be caused by temperature fluctuations, some of which may be extreme. The IPCC concluded that an increase has occurred in the frequency of hot days, hot nights, and heat waves since the release of the TAR. One of the most extreme was the European heat wave of 2003, which claimed an estimated 32,000 lives, many occurring over a very short period of time.³ France alone experienced almost 14,000 excess heat-related deaths, with a peak of 2000 heat-related deaths in one day. For August 2003, these deaths were a 60% increase over the normal August mortality rates.^35,36

 

There have been incidents of extreme heat events prior to the 2003 European heat wave. An extreme heat wave in Chicago in 1995 killed more than 700 people in a few days, and there are documented reports of excess heat deaths in London in 1995 and Belgium in 1994.^37-39 Heat waves have also increased in India (18 between 1980 and 1998) and southeast Asia, both having the greatest impact on rural populations.³ Climatologists consider it highly likely that the human influence on climate has increased the risk of heat waves such as that in Europe in 2003.⁴⁰

The consequences of such events for health care providers and the public health system will be taxing. A public health systems approach is needed to improve the coordinated response to emergencies. The burden will fall on first responders, emergency systems, safety net providers, physicians, and other health care providers. In addition to increased mortality, researchers studying the outlying effects from the 1995 Chicago heat wave found significant increased morbidity:

 

Most survivors recovered near-normal renal, hematologic, and respiratory status, but disability persisted, resulting in moderate to severe functional impairment in 33% of patients at hospital discharge. At 1 year, no patient had improved functional status, and an additional 28% of patients had died.³⁹

 

These types of events have downstream effects on physicians who will need to care for affected individuals, and heat waves are expected to increase in both frequency and duration during the 21^st century.⁴¹ Extreme heat events cause an increase in mortality due to ischemic heart disease, diabetes, stroke, respiratory disease, accidents, homicide, and suicide. In addition, heat exposure is linked to increased occurrence of heat cramps, heat syncope, heat exhaustion, and heat stroke.⁴²

 

Certain risk factors play a role in these heat events. A positive association exists between heat waves and mortality in the elderly, specifically elderly women. This is especially troublesome because the US population is aging, with an estimated population shift for persons aged 60 years and older from 19% to 32% by 2050. The mentally ill, children, individuals with occupational hazards exacerbated by increased heat, individuals with pre-existing illness, and those in socially isolated circumstances are all at risk.^31,39

 

Although extremes in cold temperatures also have been predicted, little evidence exists to directly attribute excess mortality during extreme winter temperatures to climate change. However, excess mortality from cold does occur, with variable rates among countries, especially in Europe. Interestingly, one study examining excess mortality due to cold noted that European countries with the highest winter mortality also have the mildest temperatures:

 

This positive relation has been termed the “paradox of excess winter mortality”…. Countries with comparatively warm all year climates tend to have poor domestic thermal efficiency. Because of this, these countries find it hardest to keep their homes warm when winter arrives. This is especially the case in Portugal, Spain, and Ireland, where winter temperatures are comparatively mild and excess mortality rates in winter are very high. ⁴³

 

One study indicated that the excess winter mortality in Europe may be due to poor behavioral and physiological acclimatization; people have grown accustomed to milder winters and therefore do not take additional precautions against cold. In general, however, mortality risk from cold weather extremes is expected to decline if climate change does continue to increase.³² The same acclimatization patterns may not hold true for excess heat increases due to global climate change. Increased urbanization will lead to higher density of people in areas where cooling mechanisms (such as upgraded housing with air conditioning and better ventilation) may not be well developed. In general, it is hypothesized that the higher density of people in urban areas will increase the number of heat-related deaths. ⁴¹

Flooding, caused by the interaction of rainfall, surface runoff due to deforestation, evaporation, topography, and sea level change, is the most frequently occurring natural weather disaster, affecting 1.2 billion people annually.³¹   Increased anthropogenic changes in the atmosphere and oceans have the potential to cause an “intensification in the global water cycle.”⁴⁴ Although not all floods or droughts can be attributed to these changes, the magnitude of some flooding events has intensified. In many regions, the amount of precipitation, extent of wind, and some temperature variability are affected or even determined by the El Niño-Southern Oscillation (ENSO).

 

It is unclear what effects (if any) that global climate change will have on the ENSO system. There are concerns that the ENSO may become more frequent or intense, the consequences of which cannot be overstated. In an average El Niño event, 35 per 1000 people are affected by a natural disaster, four times the rate at which people are affected in a non-El Niño year. At the least, an increase in global temperature would be predicted to increase the probability for dry weather as well as heavy rainfall, thus raising the risks for droughts and flooding in many regions. Currently, crop planning in the southern hemisphere routinely takes into account El Niño conditions, so that drought resistant crops can be planted if the weather is especially dry. The impact is so intense that ENSO conditions are routinely monitored by the insurance and financial markets in these regions.^30,45

 

In separate single seasons, flooding in China, Venezuela, and Mozambique affected 130 million, 30,000, and 2,000 people, respectively, providing a range for the potential impact on a country.³ These numbers represent those affected over the course of a single season, emphasizing the devastating and lasting effects these events can have, especially when they occur in poorer regions where response is delayed or compromised by inadequate infrastructure. A limited number of health care workers, inadequate facilities, poor transportation and roads, and lack of emergency planning are common in poor countries, making responses to extreme events more challenging. 

 

Several significant health issues are associated with flooding, including an increased risk of mortality in rapid rise flooding events due to drowning.^30,44 Increases in diarrheal diseases, such as cholera, typhoid fever, and cryptosporidiosis, occur when the endemic population already has a high incidence of infectious disease and/or poor sanitation conditions. Flooding also greatly raises the risk of water contamination by chemicals, pesticides, or heavy metals. When these substances are present in existing soil or elsewhere in the environment, they may be released during a flooding incident, causing contamination of drinking water supplies.³

 

In the United States, such contamination was present after Hurricanes Katrina and Rita in 2005, as well as after Hurricane Floyd in 1999. Diarrheal illness and death due to fecal contamination of water supplies were reported after Hurricanes Katrina and Rita, a rare event for developed countries.⁴⁶ Chemical contamination that occurred included pesticides, metals, and hazardous waste, as well as oil spills from refineries and storage tanks. Although most compounds were at acceptable levels for short-term exposure, unacceptable levels of volatile organic compounds and lead were detected in some areas. ³

 

In 1998 Hurricane Mitch dropped six feet of rain over Central America in three days. Eleven thousand people died and a cluster of disease outbreaks ensued, including malaria, dengue fever, cholera, and leptospirosis.⁴⁷ Development in Honduras is still affected by this extreme event. In addition, toxic chemicals and heavy metals concentrated in sites where cyanide is used to mine gold were mobilized during the floods, leading to water contamination.

 

In contrast to the direct effects of flooding, the effect of droughts can be more indirect. A drought usually reduces food availability in a region, leading to malnutrition, which increases the risk of both acquiring and dying from infectious diseases. ^3,48

 

Droughts also prompt population displacement, usually from rural to urban areas, which increases the risk of overcrowding, in addition to pressures for adequate shelter, food, and water. Additional associations have been found between drought and disease. For example, the “spatial distribution, intensity and seasonality of meningococcal (epidemic) meningitis appear to be strongly linked to climatic and environmental factors, particularly drought, although the causal mechanism is not clearly understood. ³

 

Much has been reported on the impact of climate change on vector-borne diseases such as malaria. This is not surprising given the global impact of the disease. Malaria continues to be one of the leading causes of morbidity and mortality in several countries worldwide, with an estimated 350 to 500 million clinical cases each year.⁴⁹ The epidemic potential of malaria transmission has been projected to increase 12% to 27% as a result of global climate change.⁴⁴ Increases in temperatures will not only lead to an increase in the population exposed to malaria, but also to greater availability of surface water for larval habitats.^50,51 Documented outbreaks of malaria have also been linked to the El Niño cycle. The rise in temperatures due to El Niño in highland areas of Pakistan, as well as increased highland temperature and rainfall in Rwanda and Uganda, also have increased transmission of malaria. ^51-53

 

Dengue has a similar global impact. Incidence of dengue has increased nearly 30-fold in the last 50 years, and it has become the most important viral mosquito-borne disease in the world. As a result, any predicted weather patterns that enlarge mosquito larval breeding grounds or allow for increased transmission of dengue have significant implications.

Climate-based (temperature, rainfall, cloud cover) density maps of the main dengue vector Stegomyia (previously called Aedesaegypti)are a good match with the observed disease distribution. The model of vector abundance has good agreement with the distribution of reported cases of dengue in Colombia, Haiti, Honduras, Indonesia, Thailand and Vietnam. Approximately one-third of the world’s population lives in regions where the climate is suitable for dengue transmission.⁵³

 

Some vector-borne disease epidemics are associated with droughts. This is true for Aedes aegypti-carried dengue fever in Caribbean islands, where water stored near houses become breeding sites for the mosquitoes. The 2004-2006 occurrence of Chikungunya fever in East Africa (more than 500,000 cases), also carried by Ae. Aegypti and Ae. albopictus, was associated with drought. ⁵⁴ 

 

Peer-reviewed research conclusively demonstrates that increased atmospheric concentrations of ozone and particulate matter causes adverse health effects in humans, especially among more sensitive populations, such as children and those with respiratory illnesses. Ground level ozone (also called tropospheric ozone) occurs from both natural and anthropogenic sources. Anthropogenic precursors of ozone are nitrogen oxides (NO_x) and volatile organic compounds (VOCs). Meteorological factors such as temperature, solar radiation, and wind affect the atmospheric concentrations of ozone. Because NO_x and VOCs can be formed through high heat combustion processes, processes involving the burning of fossil fuels generate these compounds. Accordingly, the power industry is one of the largest emitters of NO_x and VOCs, but motor vehicles, chemical plants, refineries, factories, gas stations, and paint also contribute. In addition, agricultural activities generate VOCs and NO_x from the use of diesel engines and pesticides, as well as from farm waste.^55,56 During heat waves the reaction between VOCs and NO_xs is accelerated.

 

Concentrations of ground-level ozone are increasing in developing nations. In adults, increased exposure to elevated concentrations of ozone causes an inflammatory response and damages the lung and respiratory tract epithelia. The IPCC reports that:

 

Exposure to elevated concentrations of ozone is associated with increased hospital admissions for pneumonia, chronic obstructive pulmonary disease, asthma, allergic rhinitis and other respiratory diseases, and with premature mortality. ³

 

Several studies have identified statistically significant associations between short-term increases in ozone concentrations and mortality. In a study of 95 US communities over a 13-year period (1987-2000), researchers identified a 52% increase in daily mortality when ozone concentrations increased by .010 ppm.⁵⁷ Similar results were found by a European study group. Monitoring 23 cities every three years since 1990, the group found that an increase of 10 µg/m³ in the 1-hour ozone standard (a measure of short-term exposure) corresponded to a 33% increase in mortality.⁵⁸

 

Children may be at greater risk from the adverse effects of air pollution than adults for several reasons. Children have a higher level of activity and larger minute ventilation per kilogram compared to adults, which increases the effective dose of inhaled pollutants. Second, children spend more time outdoors than adults, and third, children are still undergoing lung development. Asthmatic children using maintenance medication are more highly susceptible to the adverse health effects of ozone.⁵⁹ Particulate matter, such as black carbon, is also associated with an increase in lung diseases, such as chronic bronchitis; with lung cancer; and with the severity of asthma. Weather, including wind, temperature, and humidity, can affect the concentrations of particulate matter and ozone in the atmosphere.

Indirect health effects and mental health effects of climate change also are important:

There is increasing evidence of the importance of mental disorders as an impact of disasters. Prolonged impairment [results] from common mental disorders (anxiety and depression)….Studies in both low- and high-income countries indicate that the mental-health aspect of flood-related impacts has been insufficiently investigated. There is also evidence of medium to long-term impacts on behavioral disorders in young children. ³

 

Increases in temperature can have systemic effects on medication availability (storage and shelf life), as well as medication stability (some medications may degrade at higher temperatures). Heat can also play a role in the pharmacokinetics of several medications. Because some medications increase photosensitivity, their continued use during UV exposure may have adverse effects. ⁶⁰

The IPCC AR4 chapter on human health specifically highlights several potential populations and regions that are considered vulnerable. Expanding worldwide population will play a role in the acute effects of extreme weather events and climate change. Overpopulation taxes the resources in a region under normal circumstances; in the event of a natural or man-made disaster overpopulated regions will be under increased resource strain. Unfortunately, many of the world’s most overpopulated regions are also the poorest and are located in areas that are vulnerable to an extreme weather event, such as coastal, floodplain, lowland, or desert regions. All of these factors make the local population and the region itself more vulnerable. As noted above, these regions are likely to have inadequate infrastructure and limited health care resources to begin with, resources that would be further challenged in a time of disaster or crisis.

 

Arguably, the most vulnerable groups are those in low-lying regions, floodplains, or coastal regions. The WHO estimates that almost 25% of the world’s population lives within 100 km distance and 100 m elevation of a coa

 

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