Global warming refers to an unequivocal and continuing rise in the average temperature of Earth's climate system.Since 1971, 90% of the warming has occurred in the oceans. Despite the oceans' dominant role in energy storage, the term "global warming" is also used to refer to increases in average temperature of the air and sea at Earth's surface.Since the early 20th century, the global air and sea surface temperature has increased about 0.8C (1.4F), with about two-thirds of the increase occurring since 1980. Each of the last three decades has been successively warmer at the Earths surface than any preceding decade since 1850.
Scientific understanding of the cause of global warming has been increasing. In its fourth assessment (AR4 2007) of the relevant scientific literature, the International Panel on Climate Change (IPCC) reported that scientists were more than 90% certain that most of global warming was being caused by increasing concentrations of greenhouse gases produced by human activities.[7][8][9] In 2010 that finding was recognized by the national science academies of all major industrialized nations.[10][A] Affirming these findings in 2013, the IPCC stated that the largest driver of global warming is carbon dioxide (CO2) emissions from fossil fuel combustion, cement production, and land use changes such as deforestation.[11] Its 2013 report states
Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence has grown since AR4. It is extremely likely (95-100%) that human influence has been the dominant cause of the observed warming since the mid-20th century.
