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NASA GISS are currently the only group calculating global temperature estimates that explicitly adjust their weather station data for urbanization biases. In this study, their urbanization adjustment procedure was considered.
A number of serious problems were found with their urbanization adjustments: 1.) The vast majority of their adjustments involved correcting for “urban cooling”, whereas urbanization bias is predominantly a warming bias. 2.) The net effect of their adjustments on their global temperature estimates was unrealistically low, particularly for recent decades, when urbanization bias is expected to have increased. 3.) When a sample of highly urbanized stations was tested, the adjustments successfully removed warming bias for the 1895-1980 period, but left the 1980s-2000s period effectively unadjusted.
In an attempt to explain these unexpected problems, a critical assessment of their adjustment procedure was carried out. Several serious flaws in their procedure were identified, and recommendations to overcome these flaws were given.
Overall, NASA GISS’ urbanization adjustments were found to be seriously flawed, unreliable and inadequate. Until their adjustment approach is substantially improved, their global temperature estimates should be treated with considerable caution.
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Supplementary Information is available through the FigShare website at http://dx.doi.org/10.6084/m9.figshare.977967