It’s a while since I posted on the University of Alabama-Huntsville (UAH) temperature data, or more precisely on the global average lower tropospheric temperature anomaly as measured by satellite. The anomaly refers to the difference between the current temperature reading and the average reading for the period 1981 to 2010 as per satellite measurements.
Spencer, and his colleague John Christy at UAH, are noted climate skeptics. They are also highly qualified climate scientists, who believe that natural climate variability accounts for most of recent warming and any manmade contribution is minor. If they are correct, then we should see some flattening or even reversal of the upward trend within the UAH temperature time series over a long time period.
The last reading was for January 2015, and showed an anomaly of 0.28 degrees Celsius. This is the forth hottest temperature recorded for any January since the satellite record was started in December 1978 (37 January observations). To get a sense of the trend, see the chart here (click for larger image):
The climate skeptic community has made much of the fact that 2014 was not the hottest year on record according to satellite data. This contrasts with the time series recorded by both NASA and NOAA, which show 2014 taking the record. This is how the top 10 stack up according to UAH (taken from Spencer’s site here):
In the same post, Spencer highlights the statistical error surrounding the terrestrial hottest year claim for 2014. This is true. The reported temperatures are best estimates and sit within confidence bands. So newspaper articles should have read: “best estimate of temperature makes 2014 hottest year on record”. This doesn’t, however, make such good newspaper copy.
More important is the fact that one year’s worth of temperature is really just weather, while a decade or two is climate. Spencer has something to say about this as well:
The red flag here is “13 calendar years”. Why not ’20’? We are talking about climate after all. Critically, the 13 years takes us back to 2002 and produces the flattest line possible through the data in the chart shown above. If, by way of contrast, you take the UAH data set and compare the average temperature anomaly for the 10 years through 2014 with the average anomaly for the 10 through 2004, you see a rise of 0.13 degrees Celsius. The equivalent 20o4 to 1994 decade comparison is 0.22 degrees Celsius. So we have a slowdown, but it is far less pronounced and we still have a lot of warming.
Further, the 37 year UAH data record is still short, so a plateauing stands out. For the longer terrestrial data series, as I blogged about here, alternate fast and slow warming phases are nothing unusual. A hiatus is just that: a pause not a stop.
Critically, Spencer believes that the recent period of slow warming is evidence of low climate sensitivity to the ongoing rise in atmospheric CO2. Unfortunately, the only way he will be proved wrong about this (since he doesn’t accept consensus theory) if for the planet to undergo significant warming. This is an augment regarding which the consensus will likely be proved right, but which is far from a cause for celebration.