Global warming is the increase in the average temperature of the earth's near-surface air and oceans. It started in the mid-20th century and is projected to increase in its severity in the near future. Global surface temperature has increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the last century.

The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the observed temperature increase since the mid-20th century was caused by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation. The IPCC also concludes that variations in natural phenomena such as solar radiation and volcanoes produced most of the warming from pre-industrial times to 1950 and had a small cooling effect afterward.