aerosol influence on temperature 
The most important influence of aerosols is downwind SO2 sources, which comprise some 10% of the earth's surface. The global influence of aerosols is app. 0.5 ºC, according to the models. That means that the regions of interest must have an influence of around 5 ºC. The HADcm3 model locates the zone with the largest influence at the Finnish-Russian border. But no such influence is measurable in the surface trends at or around these locations, compared to less contaminated area's like South England or Ireland. Obvious in the trends is the influence from land/sea climate and the influence of the NOA in the different stations.


station trends
The stations were as far as possible rural one's in three groups: East is in the modeled zone in Europe (near the Finnish-Russian border) where the largest influence (4-6 ºC) should be seen in the period 1975-1990, when the anthropogenic SO2 emissions more than halved (-56%) . Middle is the zone with a medium influence (2-4 ºC at South Scandinavia/North Germany), and West is Ireland/South England (0-2 ºC).

The stations choosen from the GISS database are:
East: Vytegra, Reboly, Kajaani, Jyvaskyla (average 62.9N, 30.2E)
Middle: Visby, Leba, Lindenberg, Oslo Gardermo (marked as rural!), Schleswig-Jag (average 57.7N, 14.1E)
West: Lerwick, Shannon airport, Belmullet, Valentia obs. (average 54.7N, 7.6W)

As one can see, the largest difference in temperature in the middle and east zone's is some 2 ºC, while in the west zone it still is 1 ºC. Far less than what the model calculated. Even if we accept that the full difference in temperature is from less SO2 emissions, that means that the global influence is at maximum 0.1 ºC. But even that is questionable, as the NAO has a distinct jump in 1990 to strong positive, the same year that the temperatures in all three trends show a jump. The difference between the west trend and the two other trends can be explained by the damping influence from the oceans.

To make a comparison, here the NAO trend:
NAO trend


The influence of aerosols in current models is largely overestimated. Consequently: to fit the past trends, especially the 1945-1975 period, the models need to reduce the influence of GHGs on temperature. That besides the point that they probably underestimate solar influences too.

On the net: 21 November, 2004
Last update: 22 November, 2004

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