[1075] Of AR4 is out: humanity is very likely to cause the current climate change

The much awaited first part of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change is out. The copy is not yet available at the IPCC website and so I have not read it but according to the BBC:

Climatic changes seen around the world are “very likely” to have a human cause, the Intergovernmental Panel on Climate Change (IPCC) has concluded.

By “very likely”, the IPCC means greater than 90% probability.

The scientific body, in a report to be released formally today, forecasts temperatures will probably rise by between 1.8-4C (3.2-7.2F) by 2100.

Uncertainty, you say?

Further:

As discussions entered their final phase, the journal Science published a study comparing the IPCC’s 2001 projections on temperature and sea level change with what has actually happened.

IPCC models start from the year 1990, so that gives 16 years of data to compare.

The models had forecast a temperature rise between about 0.15 and 0.35C over this period. The actual rise of 0.33C is very close to the top of the IPCC’s range.

Graphically:

There are scientists that insist the AR4 underestimates future sea level rise. At the New York Times:

In a brief report in today’s issue of the journal Science, an array of leading climate researchers said recent findings “raise concern that the climate system, in particular sea level, may be responding more quickly than climate models indicate.”

[…]

Dr. Shindell, who emphasized that he was speaking as an individual, said, “The melting of Greenland has been accelerating so incredibly rapidly that the I.P.C.C. report will already be out of date in predicting sea level rise, which will probably be much worse than is predicted in the I.P.C.C. report.”

James McCarthy, a climate expert at Harvard who was a leader in the 2001 assessment, noted in an e-mail message that the panel’s report could be changed until the moment it was made public. Nevertheless, he said he worried that unless its discussion of sea level rise was altered, the panel would so underestimate the problem that it would look “foolishly cautious and maybe even irrelevant” on the issue.

Also at the NYT:

With the clock ticking down and translators juggling six official languages, and government representatives trying to ensure that findings do not clash with national interests, tussles have intensified between climate experts and political appointees from participating governments.

Scientists involved in the discussions said today that the U.S. delegation, led by political appointees, was pressing to play down language pointing to a link between intensification of hurricanes and warming caused by human activity.

[…]

Some scientists are suggesting that the very search for consensus may now be distracting from the need for action.

That particular article reminds me of Leggett’s The Carbon War.

Regardless, can we act now?

p/s — the summary for policymakers (SPM) of the Fourth Assessment Report (AR4) has been published. Let us read it together. If you are interested in comparing the SPM for AR4 with the previous one, do read the 2001 SPM at the UNEP. I also have the full SPM AR3 if you are interested.