Human Fingerprint on Climate Confirmed, Again

Posted on December 5, 2011

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As we all learned in math class, it’s always good to double-check your work.  And, as we also learned in math class, when double-checking, it’s even more useful to change your way of arriving at an answer.

Certain ways of solving a problem may have inherent biases and inherent weaknesses which are not apparent on the surface.  Changing your way of solving a problem prevents you from repeating mistakes you might have made before, if in fact you made mistakes.  On the other hand, if you arrive at the same conclusion from different directions, the chances of your being correct are much greater.

Thus when a group of scientists finds a new way of measuring the affect of CO2 on climate change and comparing it to other possible drivers of climate, this is welcome.

A group of Swiss climate modelers have done just that in a study published recently in Nature Geoscience.  In producing results which are “strikingly similar” to previous studies which utilized other methods, they have demonstrated the robustness of the original conclusion.

Yes, CO2 is the main driver of climate change.

At least 74% of observed climate change is caused by CO², say the scientists.

Previous studies used a technique called optimal fingerprinting to arrive at similar conclusions.

“Optimal fingerprinting is a powerful technique, but to most people it’s a black box,” says Reto Knutti, one of the report’s authors and a climate scientist at the Swiss Federal Institute of Technology.

The new approach involved running different combinations of a few crucial factors which affect Earth’s climate:  incoming energy from the Sun, outgoing solar energy, heat absorbed by oceans, albedo and other climate-feedback effects, etc.  After many thousands of test runs, they arrived at combinations which best matched the existing observed evidence.

The scientists then ran a series of tests of what happened if each factor in turn were tweaked.  They concluded that 74% of the observed warming since 1950 can only be explained by carbon dioxide forcing, a net warming value of 0.5º C out of a total observed warming of 0.55º C.  For comparison, net changes in solar radiation could have contributed no more than 0.07º C of warming, according to the study.

No, it ain’t the sun, stupid.

But given that we’ve had the warmest decade in the human record during the time of a relatively cool sun, nobody except the most stubborn climate deniers suspected the sun anyway.

Overall, the study confirms what we already knew.  It is important because it does so from a completely different direction.

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See Three-Quarters of Climate Change Is Man-Made – Scientific American