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There has been a lot of vocal complaining from the right-wing, climate denialists about some small errors and inconsistencies in the IPCC’s 2007 Fourth Assessment Report. Scant attention has been given to significant underestimates of some impacts in the 2007 report. You don’t have to delve far into the literature on sea level rise to find that many experts find the IPCC’s estimate of 20 – 60 cm rise by centuries end to be much too low.

This article at the website Real Climate titled Sealevelgate neatly summarizes the controversy. It is by Stefan Rahmstorf, an oceanographer at the University of Potsdam in Germany.

Let me propose this maxim:

For every overstatement of man’s impact on the earth’s climate by the IPCC, there is an equal and opposite understatement of some other impact.

A group of scientists has released an update to the IPCC‘s 2007 Report, called the Copenhagen Diagnosis. It includes “policy-relevant climate science published since […] the last IPCC report” and is intended to guide policymakers who will meet for climate negotiations in Copenhagen in December.

Sea Level Rise Projections from the Copenhagen Diagnosis

Overall, it indicates what many scientists already know: the Fourth Assessment Report underestimates many of the anthropogenic climate changes that are happening and likely to continue. Specifically, ice is melting faster in Antarctica and Greenland than was predicted, contributing to global sea level rise about 80% higher than earlier projections. The latest forecasts predict sea-level rise may exceed 1 meter by 2100, with a rise of up to 2 meters considered an upper limit by this time. In order to avoid the worst impacts, we must move to de-carbonize our economy, and global emissions must decline rapidly within the next five to ten years for the world to have a reasonable chance of avoiding the very worst impacts of climate change

“Carbon dioxide emissions cannot be allowed to continue to rise if humanity intends to limit the risk of unacceptable climate change. The task is urgent and the turning point must come soon. If we are to avoid more than 2 degrees Celsius warming, which many countries have already accepted as a goal, then emissions need to peak before 2020 and then decline rapidly.”

–Professor Richard Somerville, Scripps Institution of Oceanography, University of California, San Diego, USA