John Christy’s Orphan Graph
December 15, 2015
John Christy loves to use this oh-so-scientific graph when he makes his frequent appearances for climate-denying audiences. And every time, knowledgeable observer’s reaction is “WTF, where does that come from?”
But as NASA Chief Atmospheric Scientist Gavin Schmidt observes:
When it comes to temperature at Earth’s surface, with 2014 the hottest year on record and 2015 on pace to exceed even that, things are getting hot for those who deny that global warming is a danger to us all.
In their scramble to find something that looks like global warming has somehow “paused,” they seem to have settled on one particular data set with which, if you wait until just the right moment to start looking, it looks like they want it to look.
The data set du jour for deniers is the lower-troposphere temperature record from RSS (Remote Sensing Systems). It’s an estimate of the temperature in our troposphere, the lower layer of earth’s atmosphere, based on satellite measurements (but not direct temperature measurements). The usual approach is to show this data — but only part of it — then just say “no global warming” loud and long.
The latest incarnation claims that there’s been no global warming for 18 years and 5 months, meaning all the way back to the beginning of 1997. Let’s look at temperature data for the lower troposphere ourselves. But instead of the satellite data, let’s look at temperature data from actual thermometers. The satellites are great, but they measure microwave brightness, not temperature — we have to deduce how hot it is from the microwave data. That’s an extremely complex problem, and splicing together all the records from all the different satellites (there have been many) is a delicate issue. All of which is part of the reason the different groups doing so don’t agree on exactly how, or what the result is, and so often the satellite temperature data have been adjusted and revised.
For decades various organizations have been sending thermometers (and other weather instruments) up in balloons to measure the conditions at altitudes throughout the atmosphere. This has enabled us to combine the results from the long history of balloon-borne data into estimates of the temperature in earth’s troposphere.
I have in the past studied the HadAT2 data from the Hadley Centre/Climate Research Unit in the U.K. Unfortunately that data has not been kept current, it only goes as far as the end of 2012. But there are others, including the RATPAC data designed specifically for climate study and which is current through this year. The data they report which is most relevant, covering pressures from 850 to 300 hPa, is in fact for the heart of the troposphere.
Not only do these data reflect the measurements of actual thermometers, they also cover a longer time span — back to 1958 — than the satellite data which don’t start until about 1979. So here they are:
This definitely does not give the impression of any pause in warming. Of course, the truly relevant question is, has there been any real change in the trend since 1970?
Let’s use least-squares regression on the data since 1970 to see what the trend is since then:
It’s clearly upward, in fact it’s going faster than the surface temperature data. Now let’s compare that to what’s happened since 1997. Again I’ll compute a least-squares regression line and add it to the graph, but that first line was in blue so I’ll plot this one in red:
Some of you may have a hard time seeing both lines, simply because the trend-since-1997 line is right on top of the trend-since-1970 line. Their really isn’t any difference in their warming rates. If you’re color-blind it might be hard to see that there are two lines plotted, not just one.
I noticed in Roy Spencer’s latest post the following observation:
Of course, everyone has their opinions regarding how good the thermometer temperature trends are, with periodic adjustments that almost always make the present warmer or the past colder.
It’s true that adjustments at his UAH are less frequent. But when they happen, they are large. I decided to plot adjustments to UAH in this year, compared to the adjuatments in GISS (thermometer land/ocean) made over four years. The GISS version of Dec 2011 was the earliest I could find on the wayback machine. UAH brought out v6 in beta during 2015, replacing v5.6, which is however still maintained.
Update. I have found on wayback more GISS data going back to 2005 (the directory name had changed). I won’t add it to the original graph; it is too close to the other GISS to show. I’ve added below the fold a graph of differences between each dataset, new minus old, to show adjustments on a better scale. The accumulation of 10 years of “periodic adjustments” to GISS is still dwarfed by the adjustment made to UAH in 2015.
I’ve set GISS to the UAH anomaly base, 1981-2010, and smoothed the monthly data with a running 12-month mean. I’ve used reddish for UAH, and blue for GISS.
Update: I have appended a plot including GISS 2015 an RSS, with better scaling, below.
AS you see, GISS adjustments are much smaller. I should mention that if you use the GISS base of 1951-1980 the adjustments look larger. The reason is that GISS is a much longer record, and adjustments are cumulative, and the earlier base period brings in all the adjustments since 1951.
Eli has a forceful critique of UAH here. Measurement by satellite interpretation of a very indirect signal in a place that is hard to locate exactly is always going to be chancy. As Dr Mears, the man behind the RSS satellite measure, said, in discussing measurement errors:
A similar, but stronger case can be made using surface temperature datasets, which I consider to be more reliable than satellite datasets (they certainly agree with each other better than the various satellite datasets do!).
His comment on agreement was made before UAH v6, which improved the agreement, but not confidence in their stability. I suspect that UAH (and RSS) should adjust more often, but that it is not done because of the inherent uncertainty.
Difference plot below
Now it is clear that even 10 years of adjustments to GISS are small in comparison to the adjustment to UAH this year.