Updated in June 2012
Read full brief (pdf)
During the twentieth century, the earth’s surface warmed by about 1.4 °F. There are a variety of potential causes for global climate change, including natural and human-induced mechanisms. Science has made great strides recently in determining which potential causes are responsible for the climate change that occurred during the twentieth century, providing strong evidence that greenhouse gases released to the atmosphere by human activities are the main cause of contemporary global warming.