Terje Bernsten

Last week the Research Council of Norway announced the results of a new assessment of the climate system’s “sensitivity” taking into account the leveling off of global temperatures during the decade from 2000 to 2010. The study projects that a doubling of atmospheric carbon dioxide (CO2) concentrations over pre-industrial levels will increase global temperatures by between 1.2°C and 2.9°C, with 1.9°C being the most likely outcome. That is considerably cooler than the UN IPCC Fourth Assessment Report (AR4) estimate of 2°C to 4.5°C, with 3°C as the most probable outcome.

Climate sensitivity is an estimate of how much warming results from a given increase in CO2 concentrations. Estimates typically project the amount of warming from a doubling of CO2 concentrations over the pre-industrial (year 1750) level of 280 parts per million (ppm). At the current rate of increase (about 2 ppm/yr), a doubling to 560 ppm is expected by mid-century.

Climate alarm depends on several gloomy assumptions — about how fast emissions will increase, how fast atmospheric concentrations will rise, how much global temperatures will rise, how warming will affect ice sheet dynamics and sea-level rise, how warming will affect weather patterns, how the latter will affect agriculture and other economic activities, and how all climate change impacts will affect public health and welfare. But the chief assumption is the range of projected warming from a doubling of CO2 concentrations — the sensitivity estimate.

When the reseachers at the Center for International Climate and Environmental Research – Oslo (CICERO) applied their computer “model and statistics to analyse temperature readings from the air and ocean for the period ending in 2000, they found that climate sensitivity to a doubling of atmospheric CO2 concentration will most likely be 3.7°C, which is somewhat higher than the IPCC prognosis.” However, “when they entered temperatures and other data from the decade 2000-2010 into the model, climate sensitivity was greatly reduced to a ‘mere’ 1.9°C.”

Referring to the IPCC AR4 warming forecasts, project manager Terje Berntsen, a geoscience professor at the University of Oslo, commented: “The Earth’s mean temperature rose sharply during the 1990s. This may have caused us to overestimate climate sensitivity.”

No single study can make a dent on the self-anointed “scientific consensus.” But the Norwegian study is one among several recent studies that call into question the IPCC sensitivity assumptions. Cato Institute climatologist Patrick Michaels recently summarized a partial list of such studies in Forbes magazine: [click to continue…]