Temperatures of the lower troposphere: models vs. observations


Update: Just a note that this post was not intended to be anything more than a “back of the envelope” look at how global tropospheric temperatures correlate with surface temperatures as I understand the models. I’m hoping I can look more deeply into this topic in the future, mostly as an educational experience for myself.

Climate models predict that the lower troposphere should warm globally approximately 1.2 times more than the Earth’s surface (1.5 in the tropics). Yet at present, satellite temperature data does not seem entirely consistent with those predictions.

The following graph plots GISS land/sea temperatures against UAH satellite temperatures for the lower troposphere from 1979-2010 for comparison purposes.  The red line represents the GISS data and the green line plots the actual UAH temperature data. The blue line represents the GISS temperatures scaled by a factor of 1.2 and therefore shows the predicted value of the global tropospheric temperatures according to the models.

Lower Troposphere Temps (Actual vs. Predicted) (using UAH/GISS)

As can be seen, the difference between the predicted tropospheric temperatures and actual temperatures (i.e., the difference between the green and blue lines) appears to be substantial. I am not attempting to determine at this point whether the difference is statistically significant or not (I suspect it is), but that can be a topic for future post.

Now, before I’m accused of trying to mislead people, I will admit that comparing GISS temperatures to UAH temperatures is likely to produce a larger difference than comparing other temperature datasets, since GISS is generally on the high side of surface temperature records and UAH is generally on the low side of tropospheric temperatures.

To address this, I will also include a comparison of the HADCRUT3 surface temperature data with the RSS (Remote Sensing Systems) satellite temperatures of the lower troposphere. This seems like a useful complement to the above plot since HADCRUT3 is typically less extreme than GISS and RSS typically more extreme than UAH.

Lower Troposphere Temps (Actual vs. Predicted) (using RSS/HADCRUT3)

As expected, the difference between actual and observed tropospheric temperatures (i.e., the difference between the green and blue lines) is decreased in this comparison but still appears to be substantial.

In an effort to educate myself more about various issues, I will attempt to read some papers on this topic.  Apparently there is a paper by Santer from a few years back that does a comparison and concludes that the models are consistent with observed data, taking into account the error bars. I would like to understand this analysis more.

I will no doubt revisit this issue in a subsequent post and will continue to closely watch the 2010 troposphere temperatures which continue to be very high.

– Dave

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