Global warming is the rapid increase in the Earth’s average surface temperature over the past century primarily due to greenhouse gases (GHGs). It occurs when GHGs collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the Earth’s surface. Normally, this radiation would escape into space, but these GHGs trap the heat in the atmosphere and warm the planet, which is necessary to keep the earth livable. The problem is that human activities, such as the burning of fossil fuels, have amplified the planet's natural greenhouse effect and caused global warming. Since 1850, almost all the long-term warming can be explained by GHGs and other human activities.

Carbon dioxide accounts for the largest percentage of greenhouse gases (76%), followed by methane (16%), and nitrous oxide and fluorinated gases (8%). The carbon cycle has both emissions sources and carbon sinks, and their difference is the atmospheric growth.