Urban Heat Island Effect
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A new study by Watts et al shows that bad siting of temperature stations has resulted in NOAA overestimating US warming trends by 59% since 1979. The study identified a subset of 410 US Historical Climate Network stations, that have not been moved, had equipment changes, or changes in time of observations, and thus require no “adjustments” to their temperature record. These stations were classified as well sited and poorly sited, based on a WMO approved metric Leroy (2010). The news release states, "We believe the NOAA/NCDC homogenization adjustment causes well sited stations to be adjusted upwards to match the trends of poorly sited stations".
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Dr. Roy Spencer describes a new technique for for estimating the average amount of urban heat island (UHI) warming accompanying an increase in population density. The most rapid rate of warming with population increase is at the lowest population densities, while some warming continues with population increases even for densely populated cities. A population density of only 100 persons per sq. km exhibits average warming of about 1.1 deg. C compared to a nearby unpopulated temperature monitoring location.
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Climate scientists are supposed to correct the temperature record to eliminate the urban heat island effect. But they do just the opposite. They adjust rural stations to increase their warming trends. The urban warming "adjustment protocol appears to accent to a warming effect rather than eliminate it."
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Dr. Tim Ball explains how urban development affects global temperature measurements.
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NASA applies an urban correction of its GISS temperature index in the wrong direction in 45% of the adjustments. Instead of eliminating the urbanization effects, these wrong way corrections makes the urban warming trends steeper. This article discusses Steve McIntyre's audit of the GISS corrections.