What causes global warming? When fossil fuels are burned, they release large amounts of carbon dioxide, a greenhouse gas, into the air. Greenhouse gases trap heat in our atmosphere, causing global warming. When forests are cut down, much of that stored carbon is released into the atmosphere again as C02. This is how deforestation and forest degradation contribute to global warming. The consensus among climate scientists is that CO2 from tropical deforestation now makes up less than 10 percent of global warming pollution. This is one of the leading reasons of global warming