The Earth is warming at a much faster rate than normal because of many factors. Two of the most important factors are a significant increase in greenhouse gas concentrations, especially carbon dioxide, and a reduction in the Earth's ability to absorb the extra carbon load. Human activities such as burning fossil fuels, deforestation, and some agricultural land-use practices contribute to a rapidly changing climate and an overall warming of the atmosphere and oceans.

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 affect 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 dengue fever, Lyme disease, or West Nile virus to re-emerge, or spread to areas previously unaffected. Also, changes in climate can help the introduction and spread of new diseases, such as Chikungunya fever. In addition, climate directly affects the number of cases of waterborne 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.