Climate change is happening, it is caused in large part by human activity, and it will have many serious and potentially damaging effects in the decades ahead. Greenhouse gas emissions from cars, power plants and other man-made sources—rather than natural variations in climate—are the primary cause. These emissions include carbon dioxide — the main greenhouse gas — which has reached a concentration level in our atmosphere that the Earth hasn’t seen for more than 400,000 years. These greenhouse gases act like a blanket, trapping the sun’s warmth near the earth’s surface, and affecting the planet’s climate system.
