Global warming is caused by an enhanced greenhouse effect trapping heat in the atmosphere. Greenhouse gas levels like carbon dioxide and methane have increased significantly since the industrial revolution due to human activity. This additional heat in the atmosphere is causing the planet to warm, with the last century seeing surface temperatures rise 0.6-0.9 degrees Celsius. Continued warming is projected to increase temperatures 2-6 degrees Celsius by 2100 and cause serious consequences like rising sea levels displacing millions of coastal inhabitants.