(CNSNews.com) – Surface temperatures recorded over three decades at 410 ideally situated weather stations are markedly lower than temperatures recorded at stations located near multiple heatsinks, according to a new study presented Thursday at the 2015 fall meeting of the American Geophysical Union in San Francisco.
The study examined the 30-year temperature records collected from a subset of 410 weather stations belonging to the National Oceanographic and Atmospheric Administration’s (NOAA) Historical Climatology Network (USHCN) of 1,218 stations.
“A 410-station subset of U.S. Historical Climatology stations is identified that experienced no changes in time of observation or station moves during the 1979-2008 period. These stations are classified on proximity to artificial surfaces, buildings, and other such objects with unnatural thermal mass,” according to the study, entitled Comparing of Temperature Trends Using an Unperturbed Subset of the U.S. Historical Climatology Network.
“The United States temperature trends estimated from the relatively few stations in the classes with minimal artificial impact are found to be collectively about 2/3 as large as US trends estimated in the classes with greater expected artificial impact,” the researchers report.
The study “suggests that the trend for U.S. temperature will need to be corrected. We also see evidence of this same sort of siting problem around the world at many other official weather stations, suggesting that the same upward bias on trend also manifests itself in the global temperature record.”
However, “the data suggests that the divergence between well and poorly sited stations is gradual, not a result of spurious step change due to poor metadata,” they concluded.
“The majority of weather stations used by NOAA to detect climate change temperature signal have been compromised by encroachment of artificial surfaces like concrete, asphalt, and heat sources like air conditioner exhausts. This study demonstrates conclusively that this issue affects temperature trend and that NOAA’s methods are not correcting for this problem, resulting in an inflated temperature trend,” said lead author Anthony Watts, who blogs at Watts Up With That?
The best stations (Class 1) are defined as those situated on “flat and horizontal ground surrounded by a clear surface with a slope below 1/3 (<19 deg.). Grass/low vegetation ground cover <10 centimeters high. Sensors located at least 100 meters from artificial heating or reflecting surfaces, such as buildings, concrete surfaces, and parking lots. Far from large bodies of water, except if it is representative of the area, and then located at least 100 meters away. No shading when the sun elevation >3 degrees,” according to NOAA's 2002 Site Information Handbook.
The worst (Class 5) have their “temperature sensor located next to/above an artificial heating source, such as a building, roof top, parking lot, or concrete surface.”
“The poorest sites tend to be warmer,” explained co-author John Nielsen-Gammon, professor of atmospheric sciences at Texas A&M University.