Scientists believe that the Earth is warming because more greenhouse gases are being released now than in the past. Many activities release greenhouse gases. Some of these activities are burning fossil fuels for energy; transportation and manufacturing purposes; deforestation; and some agricultural and land-use practices.

Our changing climate may affect some of the things you need to be healthy such as clean air and water, enough food, and a place to live. According to the World Health Organization , about 1.2 million people worldwide die each year due to health problems caused by breathing bad air from air pollution. About 3.5 million people worldwide die because they do not get enough food to eat, and 2.2 million people get severe diarrhea because they do not have a clean water supply and proper sanitation.

Changes in climate also can impact rates infectious diseases. For example, climate change may result in changing distribution of vector-borne and zoonotic diseases prevalent in the U.S. This could cause diseases such as malaria and dengue fever to re-emerge, or facilitate the introduction and spread of new disease agents, such as West Nile virus. In addition, climate directly affects the number of new cases of waterborne diseases, like cholera, through effects on water temperature and precipitation frequency and intensity.

While climate change is recognized as a global issue, the effects of climate change will vary across geographic regions and populations.