According to the EPA, most of the greenhouse gas emissions in today's world are caused by human activities. Burning fossil fuels for transportation, heat and electricity is a major source of greenhouse gases.
The EPA estimates that around 32 percent of greenhouse gas emissions are caused by the production of electricity, and that more than 70 percent of all electricity comes from fossil fuels being burned. Fossil fuels being burned in transportation, industry, commercial and residential sectors also top the list. Surprisingly, up to 9 percent of greenhouse gas emissions come from agricultural sources, including gas produced by cows, the production of rice and agricultural soils.