Monday, August 13, 2007

More on Bad Data

Global warming is (not) in the news again, thanks to a bunch of bad data from NASA's Goddard Institute for Space Studies (GISS). A brief summary is required.

Temperature stations around the country (and globe) measure the temperature all the time. This data is handy for weathermen to say "it is 4 degrees hotter than normal today" and to look for global warming (or cooling, I suppose). Unfortunately, urbanization has crept around many of these once-rural stations, ruining their readings: concrete and buildings hold heat, and in some cases things like air conditioning have been found to blow hot air directly onto the stations.

GISS accounts for this by "adjusting" the data for urbanization. Unfortunately, it would appear that they based their adjustments to the net data on the bad stations, making the whole thing skew upward. Additionally, they seem to have some sort of Y2K bug in their programming, showing a ridiculously large jump from 2000 onward.

All this was found by amateur bloggers and scientists. Here's a few articles weighing in to state the significance of this far better than I can:
From the discoverer of the error, Steve McIntyre:

...[O[n Jan 7, 2007, NOAA announced that "The 2006 average annual temperature for the contiguous U.S. was the warmest on record." This press release was widely covered as you can determine by googling “warmest year 2006 united states”...while Schmidt describes the changes atop the leader board as “very minor re-arrangements”, many followers of the climate debate are aware of intense battles over 0.1 or 0.2 degrees... Readers might perform a little thought experiment: suppose that Spencer and Christy had published a temperature history in which they claimed that 1934 was the warmest U.S. year on record and then it turned out that they had been a computer programming error opposite to the one that Hansen made, that Wentz and Mears discovered there was an error of 0.15 deg C in the Spencer and Christy results and, after fiixing this error, it turned out that 2006 was the warmest year on record. Would realclimate[.org] simply describe this as a “very minor re-arrangement”?
Also at Coyote Blog:
In a week when Newsweek chose to argue that climate skeptics need to shut up, this incident actually proves why two sides are needed for a quality scientific debate. Hansen and his folks missed this Y2K bug because, as a man-made global warming cheerleader, he expected to see temperatures going up rapidly so he did not think to question the data. Mr. Hansen is world-famous, is a friend of luminaries like Al Gore, gets grants in quarter million dollar chunks from various global warming believers. All his outlook and his incentives made him want the higher temperatures to be true. It took other people with different hypotheses about climate to see the recent temperature jump for what it was: An error.
There's also a letter from Hansen responding to the new revelations and a response to his response here.
Hansen may have been for 1934 before he was against it. But now that he’s for 1934 once again, he can’t say that he was for it all along.

In the NASA press release in 1999 , Hansen was very strongly for 1934. He said then: The U.S. has warmed during the past century, but the warming hardly exceeds year-to-year variability.Indeed, in the U.S. the warmest decade was the 1930s and the warmest year was 1934.

However within only two years, this relationship had changed dramatically. In Hansen et al 2001 (referred to in the Lights On letter), 1934 and 1998 were in a virtual dead heat with 1934 in a slight lead. Hansen et al 2001 said:

The U.S. annual (January-December) mean temperature is slightly warmer in 1934 than in 1998 in the GISS analysis (Plate 6)… the difference between 1934 and 1998 mean temperatures is a few hundredths of a degree.
This website has all the data laid out for visual use. Enjoy.

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