Thursday, May 08, 2008

Cool on Warming

There are two poles of thought on climate. The one endorsed by Al Gore, James Hansen, most of the IPCC, and believe that atmospheric CO2 is the principal determinant in global climate and is the basis for the panic over global warming. There have been posts on RealClimate speculating on how ice ages were started and ended by variations of CO2.

The other side says that CO2 is a minor contributor along with ocean currents, solar variations, excentricities in the Earth's orbit and shifts in the Earth's axis. There are a lot of people somewhere in between these two extremes.

A new model published last week in Nature has a lot of ramifications for the CO2 crowd. This projects that changes in the Gulf Stream will cool the Earth over the next decade or so.

Climate scientists in Germany base the prediction on what they believe is an impending change in the Gulf Stream -- the conveyor belt that transports warm surface water from the tropical Atlantic to the northern Atlantic and returns cold water southwards at depth.

The Gulf Stream will temporarily weaken over the next decade, in line with what has happened regularly in the past, the researchers say.

This will lead to slightly cooler temperatures in the North Atlantic and in North America and Europe, and also help the temperatures in the tropical Pacific to remain stable, they suggest.

On one hand this takes the pressure off of the CO2 crowd. They don't have to explain why temperatures have stabilized the last decade and actually declined the last few months. This model says that this is expected but assures that global warming will eventually start up again (or that it will be there all along but masked by other fluctuations).

On the other hand, this means that Al Gore cannot keep saying that the planet "has a fever" and that all recent weather effects are caused by global warming. It also takes away a lot of the urgency. It is a lot easier to push through major changes in the global economy if you can tie it to current events instead of projected ones. (Hansen proved this 20 years ago when he testified about global warming before Congress during a heat wave in a room where the air conditioning turned off overnight.)

There is a bigger problem for the CO2 crowd. The IPCC report says that this should not happen. Figure SPM4 of the assessment report for policy makers shows observed temperatures along with plots allowing for natural forcings and anthropogenic forcings. It clearly shows that, according to the IPCC models, natural forcings are having minimal effect on the climate.

So now we have a new model that shows natural forcings having a greater effect than anthropogenic ones. This raises questions about the validity of the previous models. Is it possible that the warming that the IPCC attributed to humans was actually natural?

I checked RealClimate to see what they made of this but they have not posted since the article was announced.

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