CHUNDER DOWN UNDER
HOW GHCN v3.2 MANUFACTURES WARMING IN THE OUTBACK
by Roger Andrews
I originally entitled this post “Blunder Down Under”, but then it occurred to me that all of what I’m about to describe wasn’t a blunder at all, but intentional. So I changed “Blunder” to “Chunder”, which as those of you familiar with the Strine language will know, means “throw up”.
NCDC recently released the latest version of the Global Historic Climate Network data set – GHCN version 3.2, which applies adjustments to remove the artificial man-made discontinuities and spurious gradients that allegedly plague the “raw” GHCN Version 2 data.
I started to go through the GHCN v3.2 data, and the first record I looked at was Alice Springs in the middle of Australia. I plotted the “raw” GHCN v2 data against the adjusted GHCN v3.2 data for the station, and here’s what I got:
GHCN v3.2 adds not one, not two, but three whole degrees of warming to the Alice record since 1880.
Well, I thought, not even NCDC would do that without some justification, which it would have, for example, if the GHCN v2 records from stations around Alice all showed strong warming. So I started to download the records from surrounding stations to see what they looked like. There aren’t too many records in this area, but I found Giles 580km southwest, Halls Creek 900km northwest, Tennant Creek 460 km north, Urandangie 510km northeast, Boulia 620 km east and Oodnadatta 440km south – all of them with readings covering a period of more than 50 years, although with some gaps, most notably at Oodnadatta. The Google Earth image below shows where these stations are relative to Alice. The seven stations combined cover approximately 1.5 million sq km, or 1% of the Earth’s total land surface area.
http://oi50.tinypic.com/2d0az2u.jpgAnd here’s how the records from the six surrounding station compare with Alice:
And the seven records together show little or no warming since 1880.The match isn’t perfect, but when seven unadjusted records compare this closely we can be reasonably confident that they’re recording real and not man-made temperature changes. (The plot excludes three 2-sigma outliers; Boulia in 1893 and 1894 and Halls Creek in 1949. The 1957-84 period is used as the baseline because all seven stations were operating in those years.)
But maybe GHCN v3.2 applied warming adjustments just to Alice Springs and left the other six records intact. Did it? No, except for Tennant Creek, which for some reason receives a net cooling adjustment, it applies large warming adjustments to the other records too:
Where do these warming adjustments come from? They’re generated entirely by the algorithms NCDC applies to correct out supposed artificial discontinuities and spurious trends in the GHCN v2 data. These algorithms sound impressive when you read about them, involving as they do the use of non-parametric Kendall-Thiel paired function looping indexes and a Bayesian Information Criteria model among other things (more details here), but in many cases what they do in practice is simply adjust records that don’t show as much warming as they should to match records that do. And in this case they’ve matched the GHCN v3.2 records in the Alice Springs area to the GHCN v2 records from the much smaller Nullarbor Plain area to the south, which do show warming: (Note that “Alice Springs Area GHCN v2 Records” should read “Alice Springs Area GHCN v3.2 Records. I’ll correct this when I get time.)
There’s only one possible justification left for the GHCN v3.2 adjustments – that all the records in the Alice area except for Tennant Creek are cooling-biased by station shifts, as surmised by NCDC in its FAQ writeup here:
“Why are there more cold (negative) step changes than warm (positive) step changes in the historical land surface air temperature records represented in the GHCN v3 dataset? The reason for the larger number of cold step changes is not completely clear, but they may be due in part to systematic changes in station locations from city centers to cooler airport locations that occurred in many parts of the world from the 1930s through the 1960s.”
So I checked through the metadata for the seven stations to see whether they had all been moved from warmer downtown to cooler airport sites over the period of the GHCN v2 temperature record. I found that Alice Springs moved from downtown (?) to the airport in 1940 and Tennant Creek moved from downtown to the airport in 1969, but that was it, and neither move caused any significant shift in the temperature record, so that justification fails too.
We are now in a position to conclude that the GHCN v3.2 warming adjustments applied to the GHCN v2 records in and around Alice Springs have manufactured approximately 2C of nonexistent warming since 1880. Spread over an area of 1.5 sq km this adds only about 0.02C of non-existent warming to the global land surface air temperature series, but it adds about 0.2C of nonexistent warming to the series in the Southern Hemisphere, where there’s a lot less land.
And although I haven’t checked in detail it appears as if the GHCN v3.2 algorithms may have manufactured a lot of nonexistent warming over much of South Africa and South America too.
So while we ponder the question of whether UHI impacts, poor station quality, land use changes etc. might have introduced spurious warming into the surface temperature record, Team AGW is busily manufacturing it. And getting away with it too.