Debate On Issac Held’s Blog Titled “Temperature Trends: MSU Vs. An Atmospheric Model”

There is an interesting debate on Issac Held’s welog titled

Temperature trends: MSU vs. an atmospheric model

There is a healthy debate on this post (of which we need much more of!) that includes an insightful response which was just posted from John Christy of the University of Alabama at Huntsville

Isaac:

Someone directed me to your interesting post.  I have some comments as this is a topic with which I’m all too familiar.

1. In several papers, summarized in Christy et al. 2010, we and others investigated the accuracy of the various tropical upper air temperature datasets in detail.  It was shown that RSS contained spurious tropical warming in the 1990s due to the overcorrection for the diurnal cooling that characterizes the drifting afternoon spacecraft.  RSS was clearly the outlier (see Fig. 4.)  Thus, using RSS as the comparison does not represent the real observational evidence and portrays too much apparent agreement.

2. The comparison in the posting above does not contradict the evidence in our papers that the CMIP3 models overstate the amplification ratio.  The HiRAMC180 comparison is using a model, but tightly constrained by real temperatures, i.e. an AMIP style run. The CMIP3 coupled model runs show more warming than actually occurred in this time period (globally about twice too much) with a tropical amplification factor around 1.37 (ratio of trends Tlt/Tsfc, see Fig 10 in Christy et al.)

3. In the runs of your model I see a TLT trend of +0.148 C/decade for 1979-2009.  Observational tropical trends, as published, are +0.09 +/- 0.03 C/decade, producing an amplification ratio of 0.8 +/- 0.3 (Christy et al. 2010.)  The HiRAMC180 model indicates a scaling ratio (using trend of Tsfc as +0.12 C/decade) of 1.23 – a little less than the typical GCM, but outside of the observed ratio.

4. The same comments apply to T2 (RSS has some extra warming not found in the other datasets except for STAR which was examined in detail in Christy et al. 2011 and found also to have instituted RSS’s diurnal correction, so suffers from the same problem as RSS.)  Thus the red dots in your Fig. should be accompanied by many others further to the left (see our Fig. 10).

5. With much misinformation on this issue I want to indicate that any model/observation comparisons should be normalized (i.e. such as using the amplification ratio to eliminate variations due to volcanoes and ENSOs) and use the full tropical surface temperatures (rather than say SSTs only.)

6. Perhaps the first paper that recognized the tight coupling between tropospheric layers temperatures and the surface was Christy and McNider 1994 .

Thank you for the post and the opportunity to provide information that evidently was not used in your post.

Christy et al. 2010,  What do observational datasets say about modeled tropospheric temperature trends since 1979?  Rem. Sens., 2, doi:10.3390/rs2092148.

I recommend readers visit this post on Issac Held’s weblog to follow what is a really important issue.

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