(CBS WASHINGTON) — A World Meteorological Organization-approved reanalysis of U.S. temperature data has shown that temperatures are rising only half as much as claimed by the U.S. Historical Climatology Network (USHCN).

Monitors of temperature were moved to “more spatially representative” locations for getting accurate surface temperature trends. The analysis demonstrated that temperatures reported from 1979-2008 were spuriously doubled, with 92 percent of that over-estimation occurring because of faulty locations: being too close to urban areas where concrete, asphalt, roadways, and air conditioning system heat exchangers tainted the given temperatures.

The study’s assessment, for the years 1979 to 2008, yields a trend of +0.155 degrees Celsius per decade from the high quality sites, a +0.248 degrees Celsius per decade trend for poorly sited locations, and a trend of +0.309 degrees Celsius per decade after NOAA adjusts the data. This issue of station siting quality is expected to be an issue with respect to the monitoring of land surface temperature throughout the Global Historical Climate Network and in the BEST network.

“The new rating method employed finds that station siting does indeed have a significant effect on temperature trends,” said lead author of the research, Anthony Watts. “The previous 1999 site rating method employed to create the early metadata, and employed in the Fall et al 2011 paper I co-authored was incomplete, and didn’t properly quantify the effects.”

Previous papers all used a distance only rating system from Leroy 1999, to gauge the impact of heat sinks and sources near thermometers. Leroy 2010 shows that method to be effective for siting new stations, such as was done by NCDC adopting Leroy 1999 methods with their Climate Reference Network (CRN) in 2002 but ineffective at retroactive siting evaluation.

Using the old testing method, the study concluded that, “These factors, combined with station siting issues, have led to a spurious doubling of U.S. mean temperature trends in the 30 year data period covered by the study from 1979 – 2008.”

Other findings include, but are not limited to:

• Statistically significant differences between compliant and non-compliant stations exist, as well as urban and rural stations.

• Poorly-sited station trends are adjusted sharply upward, and well sited stations are adjusted upward to match the already-adjusted poor stations.

• Well sited rural stations show a warming nearly three times greater after NOAA adjustment is applied.

• Urban sites warm more rapidly than semi-urban sites, which in turn warm more rapidly than rural sites.

• The raw data Tmean trend for well sited stations is 0.15 degrees Celsius per decade lower than adjusted Tmean trend for poorly sited stations.

• Airport USHCN stations show a significant differences in trends than other USHCN stations, and due to equipment issues and other problems, may not be representative stations for monitoring climate.

Researchers in the current study are still investigating other issues and flaws with the old methods of climate change evaluation.


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