Global climate change
Conflicting Summer Temperatures in the Arctic?
8/22/2010, 12:02:11 PM
According to a majority of sources, the Arctic region has been experiencing the greatest increase in temperatures since the 1990's. Most sources, including satellite also showed that the Arctic was still above-normal in terms of temperature so far this summer.
On the other hand, when you look at the Danish Meteorological Institute's (DMI) Center for Ocean and Ice website, it shows that the summer north of the 80th parallel has been the coolest since records were kept going back to 1958.
The DMI estimates the daily mean temperatures in the Arctic north of 80 degrees from the average of the 00z and 12z analysis for all model grid points inside that area. The ERA40 reanalysis data set from ECMWF (European model), has been applied to calculate daily mean temperatures for the period from 1958 to 2002, from 2002 to 2006 data from the global NWP model T511 is used and from 2006 to present the T799 model data are used.
From what I have read, the T799 model has a grid resolution of 25 km.
The DMI plot of daily temperatures north of 80 degrees (red line) versus the 1958-2002 mean (green)
If you look at the Goddard Institute for Space Studies (GISS) analysis of the Arctic sea surface temperature anomalies for the Arctic and specifically 80 degrees on north for both June and July (see images below) you can see that surface temperatures were for the most part estimated to be warmer than normal.
June 2010 combined land/sea surface temperature anomalies from GISS (1200 km resloution).
GISS is able to extrapolate temperatures for the northern Arctic by using actual temperature data from stations farther south that are within 1200 km. GISS earlier determined that this method of estimation is actually quite accurate (small enough amount of error) in the northern latitudes.
I have been wondering why GISS does not consider the Danish T799 data when estimating their monthly temperature anomalies for north of 80 degrees, so I asked Dr. James Hansen, the Director of the Goddard Institute for Space Studies. Here is what Dr. Hansen said to me in his email response........
Brett...even though in certain cases it might be more accurate to use reanalysis rather than extrapolate observations, I prefer not to mix observations and models. Sometimes the extrapolations will be off in one direction and sometimes in another. If the weather patterns are such that there is a cool pool in the central Arctic, then our extrapolation is likely to misrepresent the situation. So I don't intend to leave the impression that I think it is accurate in individual situations, but I think that, on the average, it is better than omitting the Arctic, thus implicitly assuming that it has the same tendency as the average of all global regions with data.
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