The document summarizes evidence that the climate is changing faster than usual due to human activities. It discusses how scientists have measured increasing levels of CO2 and other greenhouse gases in the atmosphere since the Industrial Revolution. Measurements from Mauna Loa Observatory since 1957 show that CO2 levels have increased by 1.5-2.5% per year. The Intergovernmental Panel on Climate Change's Fourth Assessment Report in 2007 represented an overwhelming scientific consensus that climate change poses a serious risk and is at least 90% certain to be caused by human activity like burning fossil fuels. The report projected impacts of climate change like rising sea levels, stronger storms, and heat waves.