Hi All

Gary wrote...

However I remain unconviced that human activity is nothing more than a pimple on an elephant's rear when it comes to the global climate. The sun pumps power into the Earth's atmosphere at about 127 million gigawatts. The power of all human industrial activity combined is utterly insignificant compared to ordinary Solar power.

Gary

...the problem is not what humans HAVE done, though it's already noticeable, but where simple exponential growth could lead us in a real hurry. Those 12,000 terawatts are pleasant when they radiate back into space and only a bit is absorbed by the atmosphere. But if we upset balance and increase the amount returned to the ground from the atmosphere then things will get uncomfortable. There's about 10,000 terawatt years of fossil fuels in the ground that are remotely accessible - 3,000 in current conventional reserves and 7,000 of harder to extract oil-shales, tar-sands and coal only fit for gasification. Every kilogram of fossil fuel (averaged over coal, oil and gas) used produces 37 megaJoules and about 2.75 kg of CO2. There's 2 teratons of CO2 in the atmosphere - 853 terawatt years equivalent. So at most we can put about ~ 12 times the current CO2 into the atmosphere.

The Snowball Earth episodes of ~ 750 mya ended when natural volcanism increased the CO2 to 350 times current levels - the average temperature soared to 50 degrees C (vs the present 15 C.) Because the climate response to CO2 is roughly logarithmic I'd say the result of a 12 fold rise would be between the current + 33 degrees and that extreme + 68 degrees - nasty weather for most everywhere except the poles.

Eventually the oceans and the biosphere might soak it up, but not quickly - failing that in a few thousand years the geochemical cycles will get rid of it. But 86% of world energy is from fossil fuels and growing in demand at ~ 2.6% per year - more so lately thanks to India and China. The whole lot would be gone in ~ 258 years @ 2.6% growth - even quicker because the low grade stuff uses progressively more energy to extract. Achieving higher efficiency, say x 2, merely gains, at most, ~ 27 extra years.

I guess in sum: climate change could get really nasty if we burn up all the fossil fuels. To fantasise disaster for the entire planet, as some do, would be irresponsible but to advocate business as if nothing will happen is asinine too. There's only so much fossil fuel left. Even the low grade stuff could all be gone by 2100 if nothing arises to replace it.

Adam