IPCC more confident about greater uncertainty

According to an article published today in Science, "Last week's fifth assessment from the Intergovernmental Panel on Climate Change (IPCC) might appear to suggest that, in spite of decades of intensive study, scientists haven't made one whit of progress on the biggest question in climate: By how much will a doubling of atmospheric carbon dioxide (CO2) levels warm the world? But in fact, climate scientists have greatly tightened constraints on their traditional estimate of how sensitive climate may be to added greenhouse gases."

In what universe does widening the range of CO2 climate sensitivity from 2-4.5C in the last IPCC report to 1.5-4.5C in the new report constitute "greatly tightened constraints"?

In addition, the last IPCC report concluded the "best estimate" of climate sensitivity was 3C, but the new report drops this altogether, stating in a footnote that "No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies." In the upside-down, cargo-cult world of climate science, greater uncertainty means more confidence.

Science 4 October 2013:  Vol. 342 no. 6154 pp. 23-24   DOI: 10.1126/science.342.6154.23-a

• News & Analysis, Climate Science

The IPCC Gains Confidence in Key Forecast

Richard A. Kerr

Summary

Last week's fifth assessment from the Intergovernmental Panel on Climate Change (IPCC) might appear to suggest that, in spite of decades of intensive study, scientists haven't made one whit of progress on the biggest question in climate: By how much will a doubling of atmospheric carbon dioxide (CO₂) levels warm the world? But in fact, climate scientists have greatly tightened constraints on their traditional estimate of how sensitive climate may be to added greenhouse gases. And they are advancing a new way of gauging how warm it may get by century's end that is easier to estimate and of more use to policymakers.