Climate change 101: understanding and responding to global climate change

Scientists state unequivocally that the earth is warming. 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 human activities—rather than natural variations in climate—are the primary cause of contemporary global warming. Due largely to the combustion of fossil fuels, atmospheric concentrations of carbon dioxide (CO2), the principal greenhouse gas, are at a level unequaled for at least 800,000 years. The greenhouse gases from human activities are trapping more of the sun’s heat in the earth’s atmosphere, resulting in warming. Over the last century, average global temperatures rose by more than 1°F and some regions warmed by as much as 4°F. The oceans have also warmed, especially in the upper layers.