Greenhouse gases trap heat and make the planet warmer. Human activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last 150 years.1 The largest source of greenhouse gas emissions from human activities in the United States is from burning fossil fuels for electricity, heat, and transportation.
Emissions and Trends
Since 1990, U.S. greenhouse gas emissions have increased by about 4 percent. From year to year, emissions can rise and fall due to changes in the economy, the price of fuel, and other factors. In 2015, greenhouse gas emissions decreased compared to 2014 levels. This decrease was largely driven by a decrease in emissions from fossil fuel combustion, which was a result of multiple factors including substitution from coal to natural gas consumption in the electric power sector; warmer winter conditions that reduced demand for heating fuel in the residential and commercial sectors; and a slight decrease in electricity demand.