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Global warming: What about the heat-island effect?

New number-crunching confirms rising global temps

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April 2013 temperature anomalies compared to the 1951 to 1980 average.

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The escalator of global warming.

By Summit Voice

FRISCO — For years, anti-science global-warming deniers have claimed the instrumental temperature record that shows steady warming is skewed because of the so-called heat -island effect in urban areas. The instrumental temperature record shows warming of about 1.2 degrees Celsius since 1952.

The well-established global temperature record comes from thousands of readings, many from stations that are untainted by human development, and scientists account for the heat island effect when they average overall global temperatures.

And now a new study, using historical weather observations that don’t include  temperature recordings from land stations has confirmed global land warming, according to a scientist at NOAA’s Cooperative Institute for Research in Environmental Sciences. The finding refutes concerns that artifacts in land-based observing systems have led to an artificial global land warming trend. 

“Imagine that a house is built next to the thermometer that was taking the measurements,” Compo said. “How much does that affect the long-term trend at that measuring site?” “Urban warming is real, but local,” Compo said. “So you need to remove the contribution of it to try and get rid of that unrepresentative warming.”

To do that, Compo, CIRES Fellow Prashant Sardeshmukh, NOAA scientist Jeff Whitaker and their colleagues used an entirely different approach to investigate land surface temperature trends. The scientists used an approach termed the 20th Century Reanalysis (20CR), a physically based, state-of-the-art data assimilation system (see sidebar) that circumvents the problems faced in using weather station temperature data.

“20CR doesn’t have those problems because we never used a thermometer over land to determine air temperatures over land,” Compo said.

Given the variables of barometric pressure, sea surface temperature, sea-ice concentration, and carbon dioxide, volcanic and solar variations, the scientists were able to use the 20CR to infer the air temperatures over land across the globe. The derived temperatures agreed both annually and centennially with those found by weather stations. The scientists published their findings in the journal Geophysical Research Letters on April 8, 2013.

“One thing we found was that the barometer is even more valuable than we thought,” Compo said. “We were able to reproduce the hour-by-hour, day-by-day variations in temperature using only barometric pressure as a starting point.”

The agreement confirms that deficiencies in land-based station temperatures have been corrected adequately, Compo said. It also affirms that the conclusions based on large-area averages of land temperatures are robust, i.e., the climate is warming, he said.

“Do we have global warming if you only specify the sea surface temperatures and update with the pressure?” Compo said. “The answer is: yes.”

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