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on Climate Change
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Background Information > Fact Sheets
Useful Climate Change Statistics
- Due to an improved understanding of anthropogenic warming and cooling influences on climate has improved the IPCC’s Fourth Assessment Report states with very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] Watts per square metre (W/m2).
- Note 1: Radiative forcing is the change in the balance between radiation coming into the atmosphere and radiation going out. A positive radiative forcing tends on average to warm the surface of the Earth, and negative forcing tends on average to cool the surface.
- Note 2: At the Equator, the Sun provides approximately 1,000 W/m2 on the Earth's surface.
- Annual average Arctic sea ice extent shrunk by 2.7 per cent per decade. Sea-ice decreases overall in summer by 7.4 per cent.
- Temperatures at the top of permafrost layer have generally increased since the 1980s by up to 3°C.
- The maximum area covered by seasonally frozen ground has decreased by about 7% in the Northern Hemisphere since 1900 — in spring by up to 15 per cent.
- Paleoclimate information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1300 years. The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 metres of sea level rise.
- Annual fossil CO2 emissions increased from an average of 6.4 gigatons of carbon (GtC) per year in the 1990s, to 7.2 GtC per year in 2000-2005.
- CO2 radiative forcing increased by 20 per cent from 1995 to 2005, the largest in any decade in at least the last 200 years.
- For the next two decades a warming of about 0.2°C per decade is projected for a range of emission scenarios.
- Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.
- Temperatures in excess of 1.9 to 4.6°C warmer than pre-industrial sustained for millennia will lead to eventual melt of the Greenland ice sheet. This would raise sea level by 7 metres — comparable to 125,000 years ago.
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