Climate change is the environmental issue of the 21st century. Atmospheric concentrations of carbon dioxide and other greenhouse gases (GHGs) are at the highest levels they have been in Earth's history. With the Intergovernmental Panel on Climate Change (IPCC)'s 2013 report from Working Group 1 (the scientific group), strong consensus now exists that human-made GHG emissions have caused the steady increase in average global temperature chronicled during the past century.