According to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007 (IPCC FAR), there is little doubt that the Earth’s climate system is warming as a result of greenhouse gas (GHG) emissions from human activities, as evidenced by increases in global air and ocean temperatures, rising global sea levels, and widespread melting of snow and ice.
Average global temperatures have increased by 0.74°C over the past century, and warming over the past 50 years (at a rate of approximately 0.13°C per decade) has been nearly double that of the preceding 100 years.
Global sea levels have risen by approximately 1.8mm per year between 1961 and 2003 and by 3.1mm per year between 1993 and 2003. In addition, the expanse of Arctic sea ice has shrunk by 2.7% per decade since 1978.
Significant changes in precipitation have also been recorded over the last century. Increases in rainfall have been observed in some regions (including eastern North and South America, north Europe and northern and central Asia), and decreasing rainfall in others (including much of Africa, the Mediterranean region and parts of Asia).