The facts about climate change
Figure I.1
Climate change is happening, and it is happening quickly. Although the issue has been a source of controversy among scientists and policymakers, there is growing evidence that the earth’s temperature is rising and that polar ice caps and glaciers are melting. For many key parameters, the climate system is already moving beyond the patterns of natural variability (Intergovernmental Panel on Climate Change, 2007a).
Global warming is also leading to a rise in sea levels through thermal expansion of the oceans, glacier retreat, and the melting of ice sheets. Between 1993 and 2003, the global average sea level increased by approximately 3.1 millimetres. The extent of Arctic sea ice has shrunk by 2.7 per cent per decade over the past 30 years (Intergovernmental Panel on Climate Change, 2007b). During the summers of 2007 and 2008, seasonal melting created an ice-free channel in the Northwest Passage, a water route through the islands of northern Canada separating the Atlantic and Pacific oceans (United Nations Environment Programme, 2009). Antarctica is also losing ice at an unprecedented rate; it is estimated that ice loss from the West Antarctic ice sheet increased by 60 per cent between 1996 and 2006. If this ice sheet were to melt completely, sea levels could rise by as much as 5 metres (United Nations Environment Programme, 2009).
Over the past hundred years, the average temperature of the earth’s surface has increased by 0.74° C (see figure I.1) (Intergovernmental Panel on Climate Change, 2007a). The most compelling evidence of climate change has emerged over the past couple of decades, with 11 of the 12 warmest years on record occurring between 1995 and 2006 (Intergovernmental Panel on Climate Change, 2007b).
Figure I.1
3
Trends in global average surface temperature
Estimated actual global mean temperature Mean value, ºC
Differences in temperature from 1885-1990 Mean value, ºC
0.6
14.6
0.4
14.4
0.2
14.2
0
14.0
-0.2
13.8
-0.4
13.6
-0.6 1885
1905
1925
1945
Source: United Nations Environment Programme/GRID-Arendal (n.d.).
1965
1985
-13.4 2005