Another Problem With Using Surface Air Temperatures To Assess Long-Term Temperature Trends. Should Light Wind And Windy Nights Have The Same Temperature Trends At Individual Levels Even If The Boundary Layer Averaged Heat Content Change Is The Same?

The answer to this question is NO.

An October 9. 2005 article in the Seattle Times included the following,

“American researchers examined the possibility that urban heat was masquerading as global warming in 1997, by comparing data from all over the globe with measurements made only in rural areas. The warming was the same. Last year, David Parker, of Britain’s Hadley Centre for Climate Prediction and Research, settled the question emphatically by comparing measurements taken on calm and windy nights (Parker, D.E. 2004: Large-scale warming is not urban. Nature, November 18, 2004). If urbanization was making the planet look hotter than it really is, the effect should be more pronounced when there’s no wind to dissipate the heat from sweltering cities. But rates of warming were the same whether the wind was blowing or not.”

Our new paper in press at Geophysical Research Letters (GRL) “Should light wind and windy nights have the same temperature trends at individual levels even if the boundary layer averaged heat content change is the same?” has shown that the answer to this question must be no, and that the conclusions reported in the Seattle Times are incorrect. This GRL paper shows that the Parker Nature conclusions in which the temperature trends were the same on windy and light wind nights actually means that the heat content changes in the boundary layer were different!

We find that

“…if the nocturnal boundary layer heat fluxes change over time, the trends of temperature under light winds in the surface layer will be a function of height, and that the same trends of temperature will not occur in the surface layer on windy and light wind nights.”

The abstract of this new GRL paper states

“Long-term climate trends of surface air temperature should not be expected to have the same trends for light wind and stronger wind nights, even if the trends in the boundary layer heat fluxes were the same. Parker [2004] segmented observed surface temperature data into lighter and stronger wind terciles in order to assess whether the reported large-scale global-averaged temperature increases are attributable to urban warming. We conclude, however, that trends at an individual height depend on wind speed, thermodynamic stability, aerodynamic roughness, and the vertical gradient of absolute humidity. We present an analysis to illustrate why temperature values at specific levels will depend on wind speed, and with the same boundary layer heat content change, trends in temperature should be expected to be different at every height near the surface when the winds are light, as well as different between light wind and stronger wind nights. This introduces a complexity into the assessment of long-term surface temperature trends that has not been previously recognized.”

This research raises further questions as to the value of using surface air temperature data to assess global warming as well as the conclusions of the Parker Nature paper. See the weblog of July 11, 2005 entitled The Globally-Averaged Surface Temperature Trend – Incompletely Assessed? Is It Even Relevant? for other serious problems with using surface temperature data for this purpose.

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