Jim Letourneau's Blog

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Climategate didn't stamp out the climate change movement but it has got people checking their facts and more importantly, it has got people looking at the science business.

Scientists working with large digital data sets are often able to reason that a subset of data points are incorrect. Sometimes this is the case as there are many potential error sources (data entry, transposed figures, conversion errors, faulty sensors etc.). An adjustment can often be applied to the "raw" data that will remove or smooth obviously troublesome data. An "adjusted" data set is used in the subsequent interpretation.

In other cases scientists may introduce their human biases through statistical modifications. This appears to be the case with the data from the National Climatic Data Center (NCDC) according to a paper by Edward R. Long, Ph.D.

Long extracted the temperature records from rural stations and compared them to the data from urban stations. The graph below shows a warming trend in the urban data that is not observed in the rural data.

urban vs raw data

Urban heating or the heat island effect is well-documented. Cities become warmer as they grow in size. There is less vegetation and there are more artificial heat absorbing surfaces. A warming in urban temperature records would be expected during the post-war urbanization of the US and that is what the data show. The rural data does not show the same warming trend. Rather than correcting for urban heating, the NCDC …has taken liberty to alter the actual rural measured values.

In other words the NCDC "adjusted" data set is biased towards warming from the urban heat island effect. A different approach would be to adjust the urban data to reflect the trends in the rural data... but that wouldn't show a warming trend.

Long's conclusion is an important one...

This suggests the consequence of the NCDC’s protocol for adjusting the data is to cause historical data to take on the time-line characteristics of urban data. The consequence intended or not, is to report a false rate of temperature increase for the Contiguous U. S.

Anthony Watts of wattsupwiththat.com has been documenting actual temperature stations through his surfacestations.org project. His paper Is the U.S. Surface Temperature Record Reliable? doesn't mince words.

The conclusion is inescapable: The U.S. temperature record is unreliable. And since the U.S. record is thought to be “the best in the world,” it follows that the global database is likely similarly compromised and unreliable.

Volumes of peer-reviewed scientific papers have been based this "adjusted" data set so don't look for this type of work to immediately become part of the scientific consensus.

Here is some interesting background including the "professional discourtesy" (most people would use harsher language) that Anthony Watts encountered.

It is my contention that Watts is one of a new breed of gentleman scientists. The underdog will prevail.