In the past century, the average surface temperature of Earth has warmed about 0.74°C. Much of that warming has been in the past three decades. This average planetary temperature increase tends to mask the fact that temperature increases are generally greater at higher latitudes; regional climate change, therefore, has been more dramatic—in the Arctic, ice is melting rapidly and sea ice is 40 per cent thinner than it was in the 1970s. The movement of glaciers in Greenland and in much of the world is speeding up, apparently lubricated by melt water seeping down to the ice–rock boundary. The situation in the Antarctic is more complex, but change has also been documented there.
The sea level is also rising, partly as a result of melted ice but mainly because of thermal expansion as the surface layers of water heat up (water occupies more volume when it is warmer).
Most temperature recording stations around the world show that average night-time minimum and day-time maximum temperatures have both increased over the last few decades. High temperature extremes are becoming more common, such as the 2003 heatwaves in central Europe thought to have killed up to 35,000 (mainly elderly) people, and the 2003 pre-monsoon heatwave in India which had severe impacts on human health and resulted directly in the deaths of 1400 people. Although no individual event can be attributed unequivocally to climate change, the probability of such high temperature events increases with the underlying trend of rising mean temperature. According to data from the reinsurance industry, the number of climate-related disasters has increased since about 1970.
The Intergovernmental Panel on Climate Change (IPCC) published its Fourth Assessment Report (AR4) in 2007. It provides a comprehensive assessment of the latest scientific, technical and socio-economic literature produced worldwide relevant to climate change and its risks and impacts, as well as options for mitigation and adaptation. The United Nations Framework Convention on Climate Change (UNFCC) describes the current evidence of climate change. Evidence and future projected changes include higher average temperatures; more extreme weather conditions; shifts in the natural world; changes in rainfall; increased ocean temperature and acidification; sea level rise; glacial retreat and reduction in sea ice and ice sheet mass; and desertification.