Just as too little greenhouse gas makes Earth too cold, too much greenhouse gas makes Earth too warm. Over the last century, humans have burned coal, oil, and gasoline in our cars, trucks, planes, trains, power plants, and factories. Burning such fossil fuels produces CO2 as a waste product. Putting so much new CO2 into the air has made Earth warmer. If we continue on our current path, we will cause even more warming.
