The oceans are now likely effectively carbon saturated and we may be within striking distance of the 450 ppm threshold for runaway climate change, when biogeochemical processes will take over by themselves irrespective of what we do. If we are already commited to 30 years (because of the time lag) of 2 ppm carbon, that would put us up to 440 ppm:
In recent years it has become clear that the rate at which CO2 was
accumulating is itself increasing. The level currently stands at about 382 parts per million by volume (ppm), up from 315 ppm in 1958. In the past decade the rate has jumped from about 1.6ppm annually to well above 2ppm - a fact which, as The Independent reported in October 2004, may well signal that the earth's absorption ability is shrinking.
This is why James Hansen says we have less than a 10 year window to act. Hansen acknowledges that the positive feedbacks are the wild cards in the climate models. If we leave the linear regime between forcing and temperature rise, we will be entering the territory explored by James Lovelock of 10 meter sea level rises and mass die-offs.
At the same time, we are learning that current emmisions are wildly accelerating:
But from 2000 to 2004, CO2 emissions rates almost tripled to 3 per cent a year, higher than any rate used in emissions scenarios for the reports by the Intergovernmental Panel on Climate Change (IPPC).
Perhaps there is a sliver of hope in peaking levels of oil, natural gas and coal. If they all peak by 2020 as Richard Heinberg suggests (search www.energybulletin.net) and we aggressively cut back in fossil fuel consumption, perhaps we can squeeze through and preserve the planet for future generations. More study would be needed to examine this possibility.
That James Hansen has included peak oil in his latest climate predictions is a good sign, even if his numbers don't quite agree with those of Kjell Aleklett (who includes peak coal). We can only hope that the peaking of global energy can compensate for the positive feedbacks we are starting to observe.