An increase in greenhouse gases in the atmosphere is causing the planet to increase in temperature. This is causing climate change. The effects of climate change include rising sea levels, more extreme weather and more forest fires.
Humans burn fossil fuels to generate electricity, to keep buildings warm, and to power cars and other machines. Waste gases are released during this combustion, including carbon dioxide. As the human population has increased more fuel is used and more carbon dioxide is released.
Extra carbon dioxide in the atmosphere increases the greenhouse effect. More thermal energy is trapped by the atmosphere, causing the planet to become warmer than it would be naturally. This increase in the Earth's temperature is called global warming.