Feb 26 2007
Change my Mind?
In a partial response to Tamino: Question for Believers
So, IF AND ONLY IF you believe that AGW is true (i.e., that global warming is happening as a result of human activity), then: What would change your mind?
The accepted theory is that greenhouse gases warm the surface of the Earth because they are radiationally inactive to incoming shortwave solar radiation, but radiationally active to outgoing longwave Earth radiation. Yes, that’s simplified a little… or a lot. If the solar output is relatively constant and assuming thermodynamic equilibrium, then the total incoming energy needs to equal the total outgoing energy. I’m assuming the solar constant has been in fact constant over the last couple hundreds of years. I think this is true, but don’t know for sure. Also, if there is any warming or cooling of the surface or atmosphere, then the Earth is not in equilibrium. Thus, this only strictly applies to before and after any changes occur. But it doesn’t really matter, because it still needs to apply at the endpoints, which would be in equilibrium.
If the surface of the Earth is warming, then the upper atmosphere must be cooling. This must be true from a simple energy conservation argument.
The data on temperature in the upper atmosphere is a little ratty. As far as I’m aware, there is no single long-term data source that provides temperature measurements of the meso- or thermosphere. Any pointers to such data would be great. However, there are recent papers that do purport to be finding a cooling in the upper atmosphere, such as Global Change in the Upper Atmosphere in the journal Science.
Getting back to the original question, in order to change my mind I would need to see peer-reviewed papers that find no change or an increase in the upper atmosphere temperature. Because without an upper atmosphere cooling, there is no surface warming.
I’m sure there would be other things that would change my mind as well. But a warming of the upper atmosphere would be a slam dunk.
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