Does anyone know the answer to the above? I was just reading the SPARC July newsletter in which Andrew Gettelman suggested that the tropopause temperature should increase in the future due to climate change because of its effects on cloud in the TTL region. However, many years ago Thomas Reichler and I wrote a paper showing increases in tropopause temperature even for the older CM3-based coupled chemistry climate model runs at GFDL. Broadly, we identified the increase as primarily due to the increased strength of tropical upwelling. This seems to be a robust feature of climate model simulations, related as it is of course to the increased strength of the Brewer-Dobson circulation published by the celebrated author Neal Butchart. Related questions, then, are to what extent do the details of the TTL really matter, and have there been any quantitative changes in climate model predicted tropopause data? Perhaps it's the details of the TTL which give rise to the large scale average that we see in the B-D circulation. Then how good are our models at representing this upwelling change if they are relatively poor at representing the TTL region and cloud microphysics on the scale needed?
This paper which has just been published seems to suggest that the models are relatively poor:
Kociuba, Greg, and Scott B. Power. ‘Inability of CMIP5 Models to Simulate Recent Strengthening of the Walker Circulation: Implications for Projections’. Journal of Climate, 13 August 2014. doi:10.1175/JCLI-D-13-00752.1.
This paper is a little older and suggsts that "Other possible reasons for the discrepancy since 1979 are: ... neglected climate forcings."
Thorne, Peter W., Philip Brohan, Holly A. Titchner, Mark P. McCarthy, Steve C. Sherwood, Thomas C. Peterson, Leopold Haimberger, et al. ‘A Quantification of Uncertainties in Historical Tropical Tropospheric Temperature Trends from Radiosondes’. Journal of Geophysical Research: Atmospheres 116, no. D12 (2011): n/a–n/a. doi:10.1029/2010JD015487.
I have reason to believe that it is not neglected but incorrect radiative forcing which is causing problems with all climate models that incorporate the current radiation scheme. For instance there are also problems in palaeoclimatology modelling:
Robert A. Spicer, Alexei B. Herman. ‘Why Future Climate Change Is Likely to Be Underestimated: Evidence from Palaeobotany’. Journal of the Botanical Society of Bengal 67, no. 2 (2013): 75–88.
It seems that there is still work to be done. I don't have access to these papers, and I can't understand much from just the titles, but it appears that the J. Clim. paper refers to a comparison of past tropopause trends. I'm really concerned about the future, or at least past and future combined in one long simulation, and whether the numbers have changed from the CMIP3 studies. My interest in the future is that I felt that we had a good grasp of what was occurring in the model we looked at, and our conclusion would, if combined with Andrew's remarks, imply a connection between the small scale and the large scale. Has anyone actually computed tropopause trends say for the period 2000-2100 from any CMIP5 models? The GFDL model seemed to agree reasonably well with past trends as far as I can recall so the generic remark about climate models incorporating the current radiation scheme is confusing. In any case does this relate to the TTL problems identified by Andrew?
Sorry, I have no idea about the tropopause temperature trend and the specified climate models.
This paper may answer your question: Kim, J., K. M. Grise, and S.-W. Son (2013), Thermal characteristics of the cold-point tropopause region in CMIP5 models, J. Geophys. Res. Atmos., 118, 8827–8841, doi:10.1002/jgrd.50649.
They show that the CMIP5 ensemble mean shows 4K/century at 100 hPa and 1.5K/century at the cold point over the 21st century for 15N-15S in RCP8.5 scenario. This warming trend is comparable to the Chemistry Climate models, which simulate 0.5-1 K/century warming at the cold point with weaker forcing (A1B scenario).
There is an open meeting of the Royal Meteorological Society to discuss the troposphere stratosphere link later this month. See: http://www.rmets.org/events/stratosphere-troposphere-coupling-earth-system-where-next
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