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• The empirical evidence that humans are causing global warming
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• Why we can trust the surface temperature record
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• Can humans affect global climate?
• Climate Models: Learning From History Rather Than Repeating It
• Arctic sea ice... take 2
• Hansen etal hit a Climate Home Run -- in 1981
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• Arctic Sea Ice: Why Do Skeptics Think in Only Two Dimensions?
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• University of Western Australia Open Day 2010
• The main culprit in mid-century cooling
• Dust-Up On Mars: Should Martians Be Sceptical of Global Warming?
• What caused early 20th Century warming?
• The Oregon Petition: How Many Scientists Does It Take To Change A Consensus?
• How climate skeptics misunderstand past climate change
• 1934: the 47th hottest year on record
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• What were climate scientists predicting in the 1970s?
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Does the IPCC represent a scientific consensus?

What the science says...

One characterisation of the IPCC is that the IPCC is politically motivated to exaggerate the dangers of global warming and the level of human influence on climate change. When IPCC predictions are compared to observed data, the opposite is shown to be the case. For example, the acceleration in fossil fuel CO2 emissions is tracking the worst case scenarios used by the IPCC AR4 (Copenhagen Diagnosis 2009). Consequently, atmospheric CO2 is increasing ten times faster than any rate detected in ice core data over the last 22,000 years.

Figure 1: Observed global CO2 emissions from fossil fuel burning and cement production compared with IPCC emissions scenarios. The coloured area covers all scenarios used to project climate change by the IPCC (Copenhagen Diagnosis 2009).

Satellite and tide-gauge measurements show that sea level rise is accelerating faster than expected. The average rate of rise for 1993-2008 as measured from satellite is 3.4 millimetres per year while the IPCC Third Assessment Report (TAR) projected a best estimate of 1.9 millimetres per year for the same period. Actual sea level rise is 80% higher than the median projection. Sea level is likely to rise much more by 2100 than the often-cited range of 18-59 centimetres from the IPCC AR4.

Figure 3: Sea level change. Tide gauge data are indicated in red and satellite data in blue. The grey band shows the projections of the IPCC Third Assessment report (Copenhagen Diagnosis 2009).

Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. The area of sea-ice melt during 2007-2009 was about 40% greater than the average prediction from IPCC AR4 climate models. The thickness of Arctic sea ice has also been on a steady decline over the last several decades. September sea ice thickness has been decreasing at a rate of 57 centimetres per decade since 1987.

Figure 4: Observed (red line) and modelled September Arctic sea ice extent in millions of square kilometres. Solid black line gives the average of 13 IPCC AR4 models while dashed black lines represent their range. The 2009 minimum has recently been calculated at 5.10 million km2, the third lowest year on record and still well below the IPCC worst case scenario (Copenhagen Diagnosis 2009).

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