Global mean temperature in 2009 was 0.7-0.8 °C higher than in pre-industrial times and the decade 2000-2009 was the warmest on record. The Intergovernmental Panel on Climate Change (IPCC) concluded in 2007 that most of the global warming since the middle of the 20th century is very likely to have been due to human influences.
Land and ocean sinks have taken up more than half of global carbon dioxide (CO2) emissions since 1800, but these natural sinks are vulnerable to climate and land-use change and are highly likely to take up less CO2 in future.
The extent of Arctic summer sea ice has declined by about 10 % per decade since 1979. The extent of the minimum ice cover in September 2007 was half the size of the normal minimum extent in the 1950s; the third lowest minimum extent occurred in September 2010. The summer ice is also getting thinner and younger.
Observed global mean sea level rise has accelerated over the past 15 years. From 2002 to 2009 the contributions of the Greenland and West Antarctic ice sheets to sea level rise increased. In 2007 the IPCC projected a sea level rise of 0.18 to 0.59 m above the 1990 level by 2100 excluding the effects of dynamic ice sheet processes. Recent projections show a maximum increase of about 1.0 m by 2100, while higher values up to 2.0 m cannot be excluded.
The vast majority of glaciers in Europe are in retreat. Glaciers in the Alps lost about two-thirds of their volume between 1850 and 2009. The glacierised area in the Alps is projected to decrease to about one-third of the present area for a further rise in Alpine summer temperature of 2 °C.
Recent research suggests that several key components of the climate system could undergo irreversible change at significantly lower levels of global temperature increase than previously assessed. The most important of these “tipping elements” for Europe are the Greenland ice sheet, Alpine glaciers, and Arctic sea ice.