By Ken Gregory of Friends of Science

NASA’s Goddard Institute of Space Studies (GISS) publishes a global temperature index. The temperature record is contaminated by the effects of urban development and land use changes. NASA applies an “urbanization adjustment” to adjust the temperature histories to eliminate these effects. The resulting GISS temperature index is supposed to represent what the temperatures would have been in the absence of urbanization and land use changes. Most scientists assume that these adjustments are done correctly. The index is used to show that CO2 emissions are causing climate change.

An audit by researcher Steve McIntyre reveals that NASA has made urban adjustments of temperature data in its GISS temperature record in the wrong direction. The temperatures in urban areas are generally warmer than in rural areas. McIntyre classified the 7364 weather stations in the GISS world-wide network into various categories depending on the direction of the urban adjustment. NASA has applied a “negative urban adjustment” to 45% of the urban station measurements (where adjustments are made), meaning that the adjustments makes the warming trends steeper. The table below shows the number of negative and positive adjustments made to the station temperature trends.

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The urban adjustment is supposed to remove the effects of urbanization, but the NASA negative adjustments increases the urbanization effects. The result is that the surface temperature trend utilized by the International Panel on Climate Change (IPCC) is exaggerated.

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Satellite data is free of urbanization effects and provide truly global coverage continually. Previous problems with satellite drift affecting temperature calculations have been corrected. Newer satellites have station keeping capability and do not drift. The satellite data is much superior to land measurement. The satellite global temperature trend from 2002 to May 2008 is a decline of 0.25 Celsius per decade, significant global cooling for over 6 years. Read Ken’s full report here. See this informative post by Steve McIntyre here on the NASA urban fiasco. Also other reasons why GISS is warmest here.