Learn how plants respond to higher atmospheric CO2 concentrations

How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Upper Tropical Tropospheric Temperature: Simulations vs. Reality
Fu, Q., Manabe, S. and Johanson, C.M. 2011. On the warming in the tropical upper troposphere: Models versus observations. Geophysical Research Letters 38: 10.1029/2011GL048101.

The authors write that a "pronounced feature in GCM (general circulation model)-predicted climate change in the 21st century is the much enhanced maximum warming in the tropical upper troposphere near ~200 hPa (IPCC, 2007)," and they state that this feature has important implications for climate sensitivity, because of its influence on "water vapor, lapse rate and cloud feedbacks (e.g., Colman, 2001; Hartmann and Larson, 2002)," as well as its significant impact on the atmosphere's circulation, as described by Held (1993) and Butler et al. (2010). And in light of these facts, they state that it is critically important to "observationally test the GCM-simulated maximum warming in the tropical upper troposphere."

What was done
Fu et al. examined trends of temperature differences between the tropical upper- and lower-middle troposphere based on satellite microwave sounding unit (MSU) observations, after which they compared them with AR4 GCM simulations for the period 1979-2010.

What was learned
The three researchers report, first of all, that "AR4 GCMs overestimate the warming in the tropics for 1979-2010," noting that the tropical surface temperature trend from the multi-model ensemble mean is more than 60% larger than that derived from observations. Second, although they report that the satellite observations generally support GCM results with respect to tropical deep-layer tropospheric warming being greater than surface warming, they still find that the AR4 GCMs "exaggerate the increase in static stability between the tropical middle and upper troposphere during the last three decades."

What it means
Fu et al. conclude their paper by writing that "in view of the importance of the enhanced tropical upper tropospheric warming to the climate sensitivity and to the change of atmospheric circulations, it is critically important to understand the causes responsible for the discrepancy between the models and observations." And so it is that in answer to the concerned public's inquiry -- Are we there yet? -- in regard to the ability of state-of-the-art climate models to correctly foretell the planet's climatic future, we must sadly answer: No, not yet.

Butler, A.H., Thompson, D.W.J. and Heikes, R. 2010. The steady-state atmospheric circulation response to climate change-like thermal forcings in a simple general circulation model. Journal of Climate 23: 3474-3496.

Colman, R.A. 2001. On the vertical extent of atmospheric feedbacks. Climate Dynamics 17: 391-405.

Hartmann, D.L. and Larson, K. 2002. An important constraint on tropical cloud-climate feedback. Geophysical Research Letters 29: 10.1029/2002GL015835.

Held, I.M. 1993. Large-scale dynamics and global warming. Bulletin of the American Meteorological Society 74: 228-241.

IPCC. 2007. Climate Change 2007: The Physical Science Basis. Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. and Miller, H.L. (Eds.). Cambridge University Press, Cambridge, United Kingdom.

Reviewed 16 November 2011