13-17 November 2017







Concept of the Week: Human health and climate change

Climate scientists and other experts studying the projected changes in the global climate have been concerned that these changes can have potentially adverse effects upon human health. The specific health outcomes are highly uncertain. However, according to the U.S. Global Change Research Program's (USGCRP) Global Climate Change Impacts in the United States Report, several key health-related issues on the national level that could be affected by climate are: heat issues and heat waves, air quality, extreme weather events, heat associated diseases, pollen effects, and vulnerable groups.

One of the more obvious consequences of changes in climate is the increased incidence of temperature-related illnesses and deaths, especially those that would occur with heat waves, or episodes of extreme heat. Projected increases in air temperature and rising humidity levels across the nation during the 21st century would also be accompanied by increased frequency and intensity of heat waves, where air temperature and heat indices would exceed certain threshold levels for several days. In the United States, recent heat waves have resulted in numerous deaths, especially in large metropolitan areas. The elderly, the poor in urban areas and those with underlying health issues (such as diabetes and hypertension) appear to be the most susceptible to higher air temperatures and extended heat waves. Some models indicate that mortality rates would increase more rapidly in northern cities, where populations are less accustomed to the less-frequent heat waves. Using a model that includes a high emissions scenario, the average annual number of heat-related deaths in the Chicago (IL) metropolitan area could reach 700 by 2050 and 1200 by 2100.

Exposure to air pollution that would include a variety of gas species and particulate matter could result in health-related problems, especially those people with respiratory and cardiovascular diseases. Changes in climate could increase air pollutant exposure in several ways. Large-scale atmospheric circulation patterns resulting in heat waves are often stagnant, which reduce dispersion and create environmental conditions for photochemical reactions that increases ground-level ozone concentrations. Increased ozone has been shown to cause reduction in lung function. These heat waves associated with stagnant weather patterns would also increase fuel combustion for power generation needed for air conditioning. Changes in climate could also affect emissions of natural air pollutants and airborne allergens.

Certain health effects would be related to extreme weather events. In addition to above-described heat waves, increases in injuries and deaths could occur if extreme weather events such as tropical cyclones (hurricanes or tropical storms) and floods would increase in frequency. The disaster wrought by Hurricane Katrina on New Orleans, LA and the Gulf Coast in 2005 could serve as an example. Water-borne diseases can be related to water contamination caused by heavy precipitation events. A Cryptosporidium outbreak in Milwaukee, WI occurred in 1993 in which 54 people died when the municipal drinking water supply became contaminated by sewage that was not properly treated because of overtaxed storm sewers. Some climate models suggest an increased incidence of extreme weather events across the nation during a warmer 21st century, especially in the frequency of excessive precipitation events. If improvement in the sewerage and water treatment facilities are not made, projected increases in intense precipitation events could pose an increased health risk to many people, especially in the Northeast and Midwest. Chicago could have sewer overflow events going up by 50 to 120 percent in the future. In addition to the casualties that would be directly related to the natural disasters, such as drowning, some secondary effects to these disasters have been suggested, including problems with public health infrastructures and with post-traumatic stress disorder following the event.

Increases in those infectious diseases borne by insects, ticks and rodents could be possible with future changes in climate. Temperature appears to serve as a major constraint on the range of microbes and vectors, meaning that some diseases could be spread poleward with higher temperatures. While malaria, yellow fever and dengue fever have been nearly eradicated across the nation, some other diseases, such as Lyme disease and encephalitis, transmitted between humans by blood-feeding insects, ticks and mites, may occur in some areas as the result of extended spells of warm wet winters, cold springs. Rising temperatures and carbon dioxide concentrations appear to increase pollen production and lengthen the pollen season. Consequently, highly allergenic pollen could pose an increased health risk to many people.

The report also cautions that particular groups of people could be especially vulnerable to future climate change, highlighting the increases in the incidence of diabetes and obesity, which make individuals more susceptible to disease or air quality or heat.

While a range of negative health impacts would be possible from future climate change, adaptation would likely help protect the majority of the nation's population. This adaptation would entail maintenance of the public health and community infrastructure across the nation. Adequate water treatment systems would help curb waterborne diseases, while health care facilities and emergency shelters would help minimize the impacts of heat stress, air pollution, extreme weather events, and diseases transmitted by insects, ticks, and rodents.

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Prepared by Edward J. Hopkins, Ph.D., email hopkins@aos.wisc.edu
© Copyright, 2017, The American Meteorological Society.