Pollutants also affect the atmosphere through their contribution to global warming. Global warming is an increase in the Earth’s temperature. It is thought to be caused mostly by the increase of greenhouse gases like carbon dioxide. Greenhouse gases can be released by factories that burn fossil fuels. Over the past 20 years, burning fossil fuels has produced about three-quarters of the carbon dioxide from human activity. The rest of the carbon dioxide in the atmosphere is there because of deforestation, or cutting down trees ( Figure below ). Trees absorb carbon dioxide during cellular respiration, so when trees are cut down, they cannot remove carbon dioxide from the air.
Sue is very passionate about protecting the earth and wildlife. It makes her sad to see people cutting down forests to build homes or driving huge cars that burn lots of gas. This year she is planning or organizing a community project to plant more trees in her town.
Wh is causing carbondioxide levels to increase?