[Illustrations, footnotes and references available in PDF version]
Your Newsnight segment on Arctic sea ice (BBC2 TV, 8 September 2012) featured a “scientist” who said ice loss since a high point in 1979 would cut the Earth’s albedo and, by this feedback, cause warming equivalent to 20 years’ global CO2 emissions.
On the IPCC’s current central climate-sensitivity estimates, 20 years’ CO2 emissions would only warm the Earth by ¼ C°. But since the IPCC’s first projections in 1990, temperature has risen only half as fast as predicted: so make that just ? C°.
The glaciologist the programme relied on got the math wrong. Ignoring the growth in Antarctic sea ice since 1979, as the programme unwisely did, the loss of 2.5 million km2 of Arctic sea ice (measured as the linear trend on the NSIDC data) will warm the Earth by only 1/20 C°, and only then if the ice loss is permanent. Halve that to allow for the compensating effect of record Antarctic sea-ice growth: say, 1/40 C° of global warming, equivalent to just 2 years’ CO2 emissions on the IPCC’s current projections, not 20 years’ emissions. The math is below.