Climate and weather have a great deal to do with human health, and the patterns of climate change now being observed on a global scale have the potential to affect health in significant ways. The United States Environmental Protection Agency has outlined four major areas in which climate change is having an impact on human health.

Warming Trend
One of the key features of climate change is an overall warming trend. As the planet gets hotter, regions will experience an increase in the length and intensity of heat waves. Urban areas will be especially affected by these trends. Excessive heat can lead to heat-related illness and death, with the elderly, children, those with medical conditions, and the poor being most susceptible. With a greater demand for electricity for cooling, heat waves also lead to increases in air pollution caused by greater power plant output.

Extreme Weather
Another key feature of climate change is extreme weather. Increases in the incidence and severity of hurricanes, tornadoes, tropical storms, and other weather events can have profound effects on human health. In addition to direct injury, these extreme events cause flooding and disruptions in power and transportation services which in turn can reduce the availability of food and water, delay health services, contribute to carbon monoxide poisoning from portable generators, create conditions for stomach and intestinal illnesses, and affect mental health.

Warmer Temperatures
Warmer temperatures also have an impact on the production of ground-level ozone, which is a major component of smog. Increases in ozone can damage lung tissue and inflame airways, effects that exacerbate asthma and other respiratory conditions. Higher ozone levels are also associated with greater susceptibility to respiratory infections. The U.S. Global Change Research Program estimates that with the increase in warming, Red Ozone Alert days could increase by 68% in the 50 largest eastern U.S. cities. Another important factor in air quality is allergens, and warmer temperatures are known to lengthen the pollen season and promote the expansion of ragweed, an especially potent allergen.

Climate Sensitive Disease
Finally, climate change can affect human health by increasing climate-sensitive disease. Higher temperatures can allow for the easier spread of salmonella and other bacteria involved in food poisoning. The heavy rainfall and flooding associated with extreme weather events can cause overflows in sewage treatment plants that allow waterborne parasites to enter the water supply. Storm runoff can also contaminate lakes and other recreational water areas. Certain animal diseases, most notably Lyme tick disease, are extending their range because of warmer temperatures.