I've just watched a horizon episode, which appears to be scientifically sound and well conducted, the episode was called Snowball earth. Some of you may be familiar with the theory behind it.
There seems to be overwhelming geological evidence and scientific consensus in favour of a natural mechanism in place which removes Co2 from the atmosphere at an alarmingly efficient rate, and this was clearly demonstrated in earth's history, before a single plant had colonised the land.
The program suggests that 600 million years ago, thanks to volcanoes, the atmosphere contained something like 10% Co2 (as opposed to the current 0.04%) and the greenhouse effect really was significant. Without going into too much detail, the temperature was enough to unlock the earth from the grasp of a global ice age where the entire surface of the earth was covered in a thick layer of ice..
Once the ice had thawed back into liquid water, the increase in heat caused an overwhelming amount of rain due to the consiquent increase in evaporation, it was said to have rained for a hundred years. However, as rain is the cleaning agent of Co2 from the atmosphere, it became acidic as it fell and essentially locked the Co2 away as calcium carbonate crystals within the rocks of the continents, returning the atmosphere to its more stable state of atmospheric Co2 which we find ourselves in today.
10% atmospheric Co2, removed in 100 years!?
This can be summarised more concisely:
Greenhouse --> heat --> evaporation --> rain --> no more greenhouse.
No plants required. And the Greenhouse field can be any figure you like, evidently 250 times greater than what we have today, for example.
I don't see how this is consistent with the current notion of the "runaway greenhouse effect" and that we're all going to die if we don't reduce our carbon footprint by invading the 3rd world before they become industrialised or whatever it is we need to do.
In fact it seems that if we created an engine that was capable of burning the entire, very limited resources of fossil fuels on the planet within a year, and then found there was an equal amount on mars and burnt that the following year, we'd simply see a lot of rain before it all became locked up again within the rocks as calcium carbonate crystals and during the process it probably wouldn't get warmer than a few degrees.