16.1
Global warming and the surface air temperature trend in polar regions
Petr Chylek, NOAA/ERL/ARL and Dalhousie University, Halifax, NS, Canada; and G. Lesins, E. C. Weatherhead, and J. DeLuisi
Our analysis of the surface air temperature using the meteorological stations data in Arctic and Antarctic regions shows no significant trend of temperature increase during the 1900-1999 time span. On the other hand, the global temperature deduced from the meteorological stations data suggests an increasing trend of about 0.5 to 0.6K/100 years that is believed to caused primarily by an increasing concentration of greenhouse gases. The GCMs predict that the temperature increase in polar regions, due to increased concentration of greenhouse gases, should be approximately twice the global increase, that is about 1.0 to 1.2K/100 years. Thus, we have a disagreement between the observations and models' predictions concerning the behavior of the surface air temperature in polar regions. How can we reconcile this contradiction?
We propose a few possibilities: (a) The temperature measurements in polar regions are in error by a few tenths of a degree. (b) The GCM results are incorrect, at least, as far as the latitudinal distribution of the expected warming is concerned. (c) There are some other till now unidentified factors that influence the rate of temperature change in polar regions; we pursue further this possibility.
The recent GCM climate simulation done with only the natural forcing (solar variation and volcanic activity) and with the greenhouse gases kept at the pre-industrial level suggests that the earth's climate should have been cooling since 1940s. Due to the radiative forcing of added anthropogenic aerosols and greenhouse gases this projected cooling trend has been transformed into the observed global warming (with only a slight or no temperature change in polar regions). The analysis of the Vostok ice core data, for the last four interglacial periods, suggests that our current interglacial warm climate has been already lasting considerably longer (about 11,000 years)than a duration of any of the three preceding interglacial period (5,000 to 7,000 years); thus a beginning of a slow cooling trend cannot be ruled out. Consequently, the observed global climate change may be interpreted as the result of an interplay between a cooling produced by a naturally occurring factors and a warming due to anthropogenic (greenhouse gases) influences.
Session 16, Observed Variability and Change: Surface Part II (Parallel with Session 15 & Joint Session J1)
Thursday, 18 January 2001, 9:00 AM-11:44 AM
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