• Bookstore

The error affected data from 2000 to 2006 and caused an average adjustment down of 0.15-0.19°C.  The mistake was spotted when Stephen McIntyre, a Canadian climate blogger, was comparing weather station statistics and realised that there was a jump that suggested the use of different statistical models.

McIntyre searched for documentation that related to a change in methodology, but found none.  After contacting NASA with his findings, they confirmed that there was indeed an error in their calculations.  Replying to McIntyre's letter, Reto Ruedy of NASA said:
"In 2000, USHCN [United States Historical Climatology Network] provided us with a file with corrections not contained in the GHCN [Global Historical Climatology Network] data. Unlike the GHCN data, that product is not kept current on a regular basis. Hence we used (as you noticed) the GHCN data to extend those data in our further updates (2000-present)."

By extending the data in the GHCN, NASA did not notice the errors they were introducing; the errors that McIntyre noticed.  NASA agreed to amend the data to compensate for the mistake.

James Hansen, Director of NASA Goddard Institute for Space Studies, responding to finding, said:
"The flaw did have a noticeable effect on mean US temperature anomalies, as much as 0.15°C (for years 2001 and later, and 5 year mean for 1999 and later). The effect on global temperature was of order one-thousandth of a degree, so the corrected and uncorrected curves are indistinguishable."

Cover up?
In his letter to NASA, McIntyre requested for documentation to clarify the calculations that GISS use, along with source code.  This request is perfectly acceptable because NASA is a government organisation subject to Freedom of Information laws.  But, as McIntyre notes, they were "totally unresponsive."

The manner in which NASA quietly changed methodologies, and their reluctance to release details of their methods and source code, suggests to some that NASA is trying to exaggerate the extent of global warming, or even cover up the true data.

The right-wing NewsBuster blogger, Noel Sheppard, said that the lack of openness "suggests that a government agency is actually participating in a fraud against the American people by withholding information crucial to a major policy issue now facing the nation."

The target of right-wing venom is not so much GISS as James Hansen, a hate-figure among climate sceptics.  To many, rather than being scientific, Hansen is political.  Hansen, passing the error off as an insignificant "molehill" rather than the "mountain" that the "contrarians" suggest it is, responded with an attack against Corporate America:

"The real deal is this: the 'royalty' controlling the court, the ones with the power, the ones with the ability to make a difference, with the ability to change our course, the ones who will live in infamy if we pass the tipping points, are the captains of industry, CEOs in fossil fuel companies such as EXXON/Mobil, automobile manufacturers, utilities, all of the leaders who have placed short-term profit above the fate of the planet and the well-being of our children. The court jesters are their jesters, occasionally paid for services, and more substantively supported by the captains' disinformation campaigns."

McIntyre himself does not think that there is a great conspiracy, but does consider Hansen's remarks as "highly inappropriate for a federal civil servant."

McIntyre's view is that the "matter is certainly not the triviality that Gavin Schmidt would have you believe, but neither is it any magic bullet [the sceptic's view that this is debunks climate change]."

McIntyre suggests that there are three issues that need to be investigated:

• GISS failed to publicly announce that weather station data had changed.
• Can bad data be "fixed"?
• What about the rest of the world?

GISS announcement failure
McIntyre is critical of GISS' reluctance to voluntarily publicise that a change of methodology had occurred and that when McIntyre pointed out the mistake that GISS were not forthcoming in announcing that the mistake had been found.

Indeed the first public admission of error was written by NASA climate modeller Gavin Schmidt in a blog site (realclimate.org).  McIntyre suggests that "it would have been more appropriate for Gavin Schmidt of GISS (who was copied on the GISS correspondence to me) to ensure that a statement like this was on the caption to the U.S. temperature history on the GISS webpage, rather than after the fact at realclimate."

Schmidt played down the significance of the error saying that "None of these differences are statistically significant."

In response, McIntyre said:
"So while the Hansen error did not have a material impact on world temperatures, it did have a very substantial impact on US station data and a 'significant' impact on the US average. Both of these surely 'matter' and both deserved formal notice from Hansen and GISS."

Can bad data be fixed?
McIntyre's original interest was not to find mistakes in climate data, but "surface station quality".  Weather stations around the world are subject to standards that determine their placement.  In order to be able to compare data from various stations it is important that the data are not skewed by how it is placed.  For example, a weather station spotter (yes, they exist) found a temperature sensor "is kept at a comfortable temperature thanks to the nearby A/C units."  Other factors such as vicinity to buildings, trees and roads all influence the readings.

McIntyre questions whether these readings can be reliably normalised by using computer software: "the GISS software had not only failed to pick up and correct fictitious steps of up to 1°C, but that GISS actually introduced this error in the course of their programming."

It's for this reason that he asked to see their methodology documentation and source code.  As McIntyre notes:
"GISS itself has no policy against placing source code online and, indeed, a huge amount of code for their climate model is online. So it's hard to understand their present stubbornness."

What about the rest of the world?
Although criticisms have been raised about the standard of weather stations in the United States, McIntyre notes that "many of the stations in China, Indonesia, Brazil and elsewhere are in urban areas" and that in some of the major climate indices "there appears to be no attempt whatever to adjust for urbanization."  He concludes: "there is a real concern that the need for urban adjustment is most severe in the very areas where adjustments are either not made or not accurately made."