Scientists believe a major cause of global warming is the gases put into the the atmosphere by humans. Scientists agree that the burning of fossil fuels like oil and coal cause gases to escape into the air and that these gases are causing most of the warming. These gases are called greenhouse gases because they increase the natural warming effect of the atmosphere which is called the greenhouse effect (see graphic below).

Another cause of global warming is deforestation (cutting down trees). Trees soak up carbon dioxide, one of the greenhouse gases, from the air. Deforestation contributes to global warming as fewer plants are available to take up carbon dioxide from the atmosphere. In addition, as fallen trees, shrubs, and other plants are burned or allowed to slowly decompose, they release as carbon dioxide the carbon they stored during their lifetimes.

Changes in land and urbanization can also increase warming. Land-use changes can influence climate through their influence on the exchange of heat between the Earth’s surface and the atmosphere.

Additional resources

http://www.epa.gov/climatechange/                                                                                  

http://www.pewclimate.org/global-warming-basics/about

http://www.noaa.gov/climate.html