2011-07-02 07:59:25On the warming in the tropical upper troposphere: Models versus observations


New paper in press: On the warming in the tropical upper troposphere: Models versus observations Could be interesting!

IPCC (Intergovernmental Panel on Climate Change) AR4 (Fourth Assessment Report)
GCMs (General Circulation Models) predict a tropical tropospheric warming that increases with
height, reaches its maximum at ~200 hPa, and decreases to zero near the tropical tropopause.
This study examines the GCM-predicted maximum warming in the tropical upper troposphere
using satellite MSU (microwave sounding unit)-derived deep-layer temperatures in the tropical
upper- and lower-middle troposphere for 1979-2010. While satellite MSU/AMSU observations
generally support GCM results with tropical deep-layer tropospheric warming faster than
surface, it is evident that the AR4 GCMs may exaggerate the increase in static stability between
tropical middle and upper troposphere during the last three decades.


Perhaps we will read about it on Watts up with that and all the rest of it.

2011-07-02 15:21:57
Ari Jokimäki


There was another study released this week on this (Thorne et al.):

The consistency of tropical tropospheric temperature trends with climate model expectations remains contentious. A key limitation is that the uncertainties in observations from radiosondes are both substantial and poorly constrained. We present a thorough uncertainty analysis of radiosonde-based temperature records. This uses an automated homogenization procedure and a previously developed set of complex error models where the answer is known a priori. We perform a number of homogenization experiments in which error models are used to provide uncertainty estimates of real-world trends. These estimates are relatively insensitive to a variety of processing choices. Over 1979–2003, the satellite-equivalent tropical lower tropospheric temperature trend has likely (5–95% confidence range) been between −0.01 K/decade and 0.19 K/decade (0.05–0.23 K/decade over 1958–2003) with a best estimate of 0.08 K/decade (0.14 K/decade). This range includes both available satellite data sets and estimates from models (based upon scaling their tropical amplification behavior by observed surface trends). On an individual pressure level basis, agreement between models, theory, and observations within the troposphere is uncertain over 1979 to 2003 and nonexistent above 300 hPa. Analysis of 1958–2003, however, shows consistent model-data agreement in tropical lapse rate trends at all levels up to the tropical tropopause, so the disagreement in the more recent period is not necessarily evidence of a general problem in simulating long-term global warming. Other possible reasons for the discrepancy since 1979 are: observational errors beyond those accounted for here, end-point effects, inadequate decadal variability in model lapse rates, or neglected climate forcings.

2011-07-02 21:00:13
Mark Richardson

The lapse rate feedback is a negative one. When the skeptics talk about this (and also say in the same presentation that evaporation is going faster than models predict), I'm pretty sure they're tying themselves in knots.


WV + LR together are pretty constant. Bigger lapse rate feedback means more evaporative cooling, but greater warming aloft increases higher specific humidity. And vice versa...

Soden & Held, 2006 showed that modeled climate change is pretty much independent of the size of hte tropospheric hot spot, and that models predict a range of sizes for it.