Fingerprinting Climate Change

I'd like to think I helped inspire Krugman to write his column today, since he linked here the other day from his blog.  Hardly anyone reads this thing, but if the right people read it, maybe it can have some second-hand impact?  This and my slightly easing schedule inspires me to try getting back to it.

Hansen's climate dice paper shows how much the relative frequency of extremely warm temperatures has increased.  But how is it that scientists know warming is due to greenhouse gas concentrations (primarily CO2)?

Earlier this summer I got to attend a workshop in Banff on climate change detection and attribution, a research area dedicated to precisely this question.  Besides a few token impacts guys like myself, the workshop was attended mainly by top people in detection and attribution.  It was interesting for me to see the technical side of this, which basically involves some sophisticated statistical modelling.

The basic idea is to look at how the "fingerprint" of warming matches the core predictions of the various climate models.  This fingerprint includes much more than the amount of surface-temperature global warming.  They pay attention to the pattern of warming across different latitudes.  The climate models predict more surface warming in the polar regions and especially the north, as compared to equatorial regions. Most compelling to my mind, is the fingerprint of predicted warming and cooling in different layers of the atmosphere.   Unique to greenhouse gas emissions, the models actually predict cooling in the lower stratosphere, but more warming in the upper troposphere in equatorial latitudes.  I understand physicists predicted this distinct fingerprint before they had even begun measuring temperatures throughout the troposphere and stratosphere. 

Here is a picture from Ben Santer's talk that illustrates the model-predicted pattern of warming from GHG in comparison to other factors that might cause warming.

And here's what data on actual warming look like:

In a nutshell, this is why the real climate scientists--about 97% of them--are not only convinced that climate change is real, but that it is due to greenhouse gas emissions and is human induced.
(If you dig around the link to the workshop you can find a video of my talk on agricultural impacts....)


  1. Michael-- I understand the point of this posting, that climate model predictions appear to match observations. However, the data is difficult to interpret in the above forms. Clearly, pressure decreases as one moves higher in the atmosphere, so the y-axis of the bottom graph is related to the y-axes of the graphs above, but how exactly? Also, what are the units of the x-axis of the bottom graph?

  2. The units for the x axis are probably degrees of latitude north(+) and south(-) of the equator.

  3. I read your blog. I am not as important as Krugman, no second-hand impact here, but I appreciate you take time to write on the blog. Thanks from Argentina.


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