The probable warming curve could match the increase of airliner activity and there are studies argueing that high clouds tend to have a warming effect. And the areas that experienced the most warming (Northern hemisphere contiments, especially Europe) also have the greatest density of airline traffic. Moreover, the water vapor brought in at higher levels is just about the strongest nmatural greenhouse gas. However satelite observation show a cooling trend at higher altitudes, attributed to the thinning of the ozone layer.
Other possible causes that are seldomly mentioned:
- Direct absorbtion of energy in the lower atmosphere by soot and haze
- decreasing albedo (reflectivity) of the earth surface due to reforrestation and urbanisation
- abnormal oceanic behaviour (increasing strong el ninos) enhanced THC, etc
- abnormal weather flow patterns, increasing the equator to polar circulation, effectively transporting more tropical heat to the moderate areas.
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