The greenie's argument for global warming is based on computer models. We know how much energy the Sun pours onto the earth. (1345 Watts/sqm * area of the earth = 1.78 *10 **17 Watts) We know that the earth's temperature has remained reasonable steady thruout geological time. That means the earth has to throw off, by infrared radiation, or reflection the same amount of energy. If it didn't, the temperature would go up (or down).
Clouds are an important factor. Anyone who has stood on the beach in a bathing suit and felt the chill when a cloud goes in front of the Sun will have no problem believing that clouds cool the earth, by reflecting sunlight back into space. Less well known, unless you live in the north, clouds warm the earth. A clear winter night will get extremely cold, (-20 F) whereas a cloudy night will stay at +20F. On clear nights, the earth will emit infra red radiation, which travels up and away to interstellar space. This energy loss cools the world. On cloudy nights, the same infrared radiation strikes the cloud, warming it, and the air it floats in, and conserving the heat.
Which effect is stronger? I have never seen any discussion of that. I don't think anyone knows. What's more, it is generally assumed that a rise in global temperature will increase evaporation of water, increasing cloud coverage. If increasing clouds cool the earth, fine, that will limit the temperature rise. If increasing clouds warm the earth, hang onto your hats, as the earth warms, the clouds increase,which increases the warming. Bad.
But, until the effect of clouds is understood, and programmed into the computer models, they are worthless. Without an accurate treatment of cloudiness, the model's results will bear no resemblance to reality.
And those claiming "the science is settled" are peddling ideology, not science.
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