Originally Posted by loki
What are the really big natural causes of global warming? we hear so mch about the man made ones, but what natural causes of global warming are also responsible?
The longest term one is alteration in the Earth's distance from the Sun - the orbit does change over very long periods and thus could have an effect.
More rapidly, natural release of greenhouse gases such as methane from the rocks.
Cloud cover can be very important - if clouds become more estensive then solar radiation cannot reach the lower atmosphere: so one concern is that melting the ice caps will cause increased cloud which will lead to rapid cooling of the Earth.
Severe volcanic eruptions cast fine powder into the atmosphere and this can have similar or contradictory effects by either repelling radiation *or* by trapping heat! They also release greenhouse gases ...
But the bigest overall effect has been caused by the evolution of plants and animals. The greenhouse effect only came into being by the evolution of green plants which used up lots of carbon dioxide and produced lots of oxygen - thus allowing the evolution of animals. The balance between plants and animals effectively determines the chemical composition of the atmosphere (the main component is nitrogen and unaffacted by this, I think) so as numbers of plants/animals vary, then so does the O2:CO2 ratio. Apart from releasing trapped carbon, humans are affecting the balance by chopping down trees and growing cows!
That's the best I can do