Duan, A. (2007), Cooling trend in the upper troposphere and lower stratosphere over China, Geophys. Res. Lett., 34, L15708, doi:10.1029/2007GL029667.

Abstract: A strong cooling trend (?0.62°C per decade) in the upper troposphere and lower stratosphere (UTLS) over China is detected based on the records of 109 radiosonde stations during the period from 1980 to 2004. In contrast, the underlying mid and lower troposphere (MLT) exhibits a relatively weak warming trend (0.17°C per decade) with the largest magnitude at the surface. Accompanying these changes in air temperature, large-scale circulation associated with the monsoon activity in East Asia declines remarkably in both winter and summer. Meanwhile, decreasing trend of the total ozone amount has also been found in the same period. Numerical simulations using two global coupled climate models further suggest that the ozone depletion and enhanced anthropogenic greenhouse effect play an important role in the cooling of UTLS and warming of MLT.

Stratospheric cooling is one of the two virtually certain projections made by the theory of global warming due to greenhouse gases. [Mahlman, 1997] In terms that the IPCC would use, and indeed Mahlman uses them too, it is “virtually certain” that stratospheric temperatures will decrease. It is difficult to explain why the addition of a greenhouse gas (CO2) would actually cool part of the atmosphere. The difficulty does not arise from the physics; the physics are well understood. The difficulty is two-fold; the atmosphere is an extremely complex system, and it is difficult for a non-expert (especially a lay person) to understand the subtleties.

Here’s an explaination of why the addition of CO2 will cool the stratosphere from William Connolley [I've edited the quote for readability, but not for context.]

In a uniformly grey non-convecting atmosphere (ie, if the atmosphere were equally transparent at all wavelengths, and uniformly through its depth) heated from below (ie, solar radiation warming the surface; assuming of course that we’ve relaxed the grey assumption to let the solar through), then increasing the greenhouse gases (GHG’s) doesn’t lead to a cooling at the top: instead, the whole atmosphere warms, though not uniformly. You can see some calculations, pictures and code here.

Of course, the real atmosphere does convect, and isn’t totally transparent to solar, but the real difference is that the real atmosphere has a stratosphere, a region of the atmosphere that temperature increases with height because of ozone absorbing ultraviolet radiation.

Hence the stratosphere is considerably warmer than it would be under just longwave (LW, or IR) forcing, and CO2 is only effective in LW frequencies. Hence, increasing CO2 increases the stratospheres ability to radiate in the LW, but doesn’t substantially increase its ability to gain heat, because most of that comes from the SW. Hence it cools.

In the troposphere, ignoring convection etc., increasing CO2 increases both the ability to gain and lose heat, and this first-order argument doesn’t tell you what will happen. As it turns out, it warms.

Duan concludes:

This research revealed that there is a strong cooling trend in UTLS and a relatively weak warming trend in the underlying MLT over China during recent decades. The largest magnitudes of trends occur in late winter and summer. The corresponding change in the circulation is characterised by the depressed monsoon activity in both winter and summer. Two coupled climate models successfully reproduce the cooling trend in UTLS and warming trend in MLT since late 1970s when the models are forced by historical CO2 and total ozone data. It implies that the ozone depletion and enhanced anthropogenic greenhouse effect play an important role in the cooling of UTLS and warming of MLT. [Emphasis mine.]

This paper not only shows that a virtually certain projection of greenhouse theory is being observed, it shows that the observed temperature is the same as the models predict.

References:
Mahlman, J.D., Uncertainties in Projections of Human-Caused Climate Warming, Science 21 November 1997: Vol. 278. no. 5342, pp. 1416 - 1417. DOI: 10.1126/science.278.5342.1416

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