Greenhouse gas
Greenhouse gases are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F).
The most abundant greenhouse gases in Earth's atmosphere, listed in decreasing order of average global mole fraction, are: Water vapor (H
2O), Carbon dioxide (CO
2), Methane (CH
4), Nitrous oxide (N
2O), Ozone (O
3), Chlorofluorocarbons (CFCs and HCFCs), Hydrofluorocarbons (HFCs), Perfluorocarbons (CF
4, C
2F
6, etc.), SF
6, and NF
3. Yet, while water vapor is a potent greenhouse gas, humans are not directly adding to its concentrations,. so it is not one of the primary drivers of climate change, but rather one of the feedbacks. On the other hand, carbon dioxide is causing about three quarters of global warming and can take thousands of years to be fully absorbed by the carbon cycle. Methane causes most of the remaining warming and lasts in the atmosphere for an average of 12 years.
Human activities since the beginning of the Industrial Revolution (around 1750) have increased atmospheric methane concentrations by over 150% and carbon dioxide by over 50%, up to a level not seen in over 3 million years. The vast majority of carbon dioxide emissions by humans come from the combustion of fossil fuels, principally coal, petroleum (including oil) and natural gas. Additional contributions come from cement manufacturing, fertilizer production, and changes in land use like deforestation.: 687 Methane emissions originate from agriculture, fossil fuel production, waste, and other sources.
According to Berkeley Earth, average global surface temperature has risen by more than 1.2 °C (2.2 °F) since the pre-industrial (1850–1899) period as a result of greenhouse gas emissions. If current emission rates continue then temperature rises will surpass 2.0 °C (3.6 °F) sometime between 2040 and 2070, which is the level the United Nations' Intergovernmental Panel on Climate Change (IPCC) says is "dangerous".