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Originally Posted by mitheral
I believe tw is talking about Global Dimming which is the observed fact that the brightness of the sun at ground level declined about 5% between the 1950 and 1990. This dimming it's postulated was caused by particulate pollution which has been reduced due to measures like the Clean Air Act in the USA. |
Global warning was recently connected with activity of man. That part is no longer disputable. However details of the mechanism(s) involved are still being learned. Another piece of the puzzle has been identified: From BBC News of 12 Nov 2005:
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Water builds the heat in Europe
The scientists say that rising temperatures caused by greenhouse gases are increasing humidity, which in turn amplifies the temperature rise.
This is potentially a positive feedback mechanism which could increase the impact of greenhouse gases such as CO2. ...
"We observed that between 1995 and 2002, the amount of longwave radiation coming downwards to the Earth in Europe increased significantly, whereas solar radiation did not," said study leader Rolf Philipona, from the World Radiation Center in Davos, Switzerland.
Longwave radiation comes from molecules of gases such as carbon dioxide, methane, and water vapour which have absorbed solar radiation after it has hit the Earth's surface and been reflected back up through the atmosphere.
"We wondered if this effect was simply because of a temperature increase at the surface - you would just get more radiation going up, and so more coming back down," Dr Philipona told the BBC News website.
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