U.S. Climate Action Network
Contact: Daniel A. Lashof, Natural Resources Defense Council,
(202) 783-7800
U.S. Climate Action Network
Contact: Daniel A. Lashof, Natural Resources Defense Council,
(202) 783-7800
Global climate change poses substantial risks to human health. Millions of people could be affected, and the IPCC anticipates that most of the impacts would be adverse. Increases in mortality from heat waves compounded by more severe urban air pollution are predicted with high confidence. Increases in infectious diseases, such as malaria and schistosomiasis, are also predicted with high confidence, due to the geographic spread of conducive climatic conditions and changes in the lifecycle of disease vectors and infectious organisms. Finally, other impacts of climate change, such as sea-level rise and increases in drought, would also adversely affect public health by increasing hunger in some areas, by damaging infrastructure and by displacing populations.
The sustained health of human populations requires the continued integrity of Earth s natural systems. The disturbance, by climate change, of physical systems and of ecosystems would therefore pose risks to human health.
Extensive research has shown that heat waves cause excess deaths. The IPCC predicts, with high confidence, that climate change will cause additional heat-related deaths and illnesses. Studies in selected cities in North America, North Africa, and East Asia indicate that the number could more than double by 2050, representing several thousand extra deaths annually in a number of very large cities. Heat-related deaths are concentrated among vulnerable populations, such as the elderly and the very young, and are mostly associated with preexisting cardiovascular and respiratory disorders. Poverty and poor housing are exacerbating factors. Although some of the excess deaths recorded during heat waves represent individuals who would have died within a few weeks in the absence of the heat event, this appears to account for only 20 40 percent of the cases. Global warming will also cause some decrease in winter mortality, but the IPCC concludes that overall there is likely to be a net increase in weather-related deaths.
The effects of heat are amplified by stagnant air, high humidity and high levels of air pollution. As use of coal and oil generally results in significant emissions of local air pollutants as well as greenhouse gases, high levels of urban air pollution are likely to be associated with global warming. Furthermore, higher temperatures directly enhance the chemical reactions that produce urban smog (i.e., tropospheric ozone).
Vector-borne diseases are a major cause of illness and death in tropical countries. Rather than being transmitted directly from human to human, these diseases are transmitted by insects or other vectors. Climate is an important determinant of the spread of vector-borne diseases, affecting the distribution of the disease-carrying insects as well as the infectiousness of the disease itself. The IPCC concluded that In general, increased warmth and moisture would enhance transmission of these diseases. Vector-borne diseases that the IPCC considers very likely or highly likely to be affected by climate change include malaria, schistosomiasis, onchocerciasis (river blindness), dengue, and yellow fever . Malaria is a central example. Malaria is caused by a parasite (plasmodium) and is transmitted from human to human by mosquito vectors. About 300 million new cases of malaria occur each year. The anopheline mosquitos that are the most important vector for malaria generally require mean winter temperatures above 60 Fahrenheit (F) to survive.
Temperatures above 64 F are required for the parasite to be actively infectious. Warmer temperature speed up the lifecycle of the parasite and increase infectiousness. One model reviewed by the IPCC estimates that global warming could increase the potential malaria transmission zone to an area that includes 60 percent of the world's population, compared to 45 percent under current climate conditions This model predicts a climate-induced increase of 50-80 million cases of malaria annually in response to a global mean temperature increase of about 5 degrees Fahrenheit. Although this quantitative result must be viewed cautiously, and does not account for the potential for public health measures to mitigate the impact, it clearly indicates the magnitude of the potential impact of climate change on public health.
Other types of infectious disease could also increase due to climate change. Warmer temperatures and increased flooding, for example, could increase contamination of drinking water, leading to diarrheal and dysentery epidemics. Cholera, in particular, can survive in sea water when sheltered beneath the mucous outer coat of various algae and zooplankton. Increases in coastal algal blooms, which would be promoted by warming, could therefore amplify cholera proliferation and transmission. Finally, public health will also be threatened by the consequence of other adverse effects of climate change, such as increases in malnutrition in some areas, damages to sanitation infrastructure, and the creation of refugees from sea-level rise and storm surges.
More than 500 deaths were caused by an intense heat wave that struck the midwest U.S. during the summer of 1995. Although it is not possible to attribute this (or any other) particular event to global climate change, it is the type of event that is projected to become more frequent due to global warming. For example, the IPCC presents results of a study for Atlanta which projects that the number of heat-related deaths would increase from an average of less than 80 per year currently to 150 440 per year in 2050, depending on the climate change scenario and the ability of the population to acclimatize to warmer conditions.
Global warming could also lead to U.S. outbreaks of infectious diseases that are currently confined to more tropical countries. For example, local transmission of malaria could become possible in much of the U.S. by the middle of the next century. As travelers already bring several cases of malaria into the U.S. each year, local epidemics are possible. despite the strong public health infrastructure in the U.S. compared to poorer countries. Recently 13 cases of dengue fever have been confirmed in and around McAllen, Texas. Dengue fever (also called break bone fever ) is transmitted by the Aedes aegypti mosquito, whose range and infectiousness depend strongly on warm temperatures. According the IPCC report, an increase of 5 7 F in average temperature doubles the rate of transmission of the dengue virus. Dengue has recently reemerged in Central America and spread in Mexico. Local transmission is suspected in the Texas cases, but is difficult to confirm.