This idea of two stable states has been pushed recently by Jim Lovelock, however I think there is very little evidence to support such a view.
Just about every model result indicates monotonically and more-or-less continuously increasing effect with increasing doses of CO2 (or changes in sunlight). [Of course, the models are a gross simplification of reality.] There are a few sources of metastability (eg, large ice sheets) but I do not think that these sources of metastability govern the overall behavior of the system on sub-millennial time scales. ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected] http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 On Mon, Dec 7, 2009 at 6:22 AM, John Nissen <[email protected]> wrote: > > Hi all, > > I've a simple picture of the situation. Think of the Earth system as a > bus, with automatic speed control mechanism to keep the bus between two > speeds - a top speed and a bottom speed. When the bus gets to the top speed > the brakes automatically come on and the throttle starts closing. Then when > it has slowed to the bottom speed the brakes automatically come off and the > throttle starts opening again. This mechanism has worked for over a million > years, keeping the bus running between higher and lower speeds, without the > driver doing anything. > > [*Global temperature has oscillated between a top and bottom temperature > over the course of the Ice Ages. The Arctic sea ice is probably involved in > preventing the temperature going above the top limit. CO2 may be involved > in preventing the temperature going below the bottom limit*.] > > Then, about 8000 years ago, when the bus was near its top speed, the driver > took over control. Although the brakes were starting to come on, the > throttle was kept open by the driver by just the right amount to keep the > bus going at the higher speed. This kept the passengers extremely happy! > They thought this situation would carry on for ever, but this proved to be > wishful thinking. > > [*By amazing chance, mankind's inadvertent emissions of CO2 and methane > have kept global temperature, and hence sea level, pretty constant for about > 8000 years, thus allowing the emergence of civilisation.*] > > Then suddenly, a hundred years ago, the driver started opening the throttle > more than it had ever been before, whilst at the same time taking off the > break. Surprise, surprise, the bus started to accelerate. Some passengers > refused to see the danger - they were enjoying the speed, and were happy for > the driver to open the throttle even more. Other passengers saw the > danger. The passengers broke into argument, and eventually agreed on a > compromise to gradually stop opening the throttle, although it was realised > the bus could reach a dangerous speed. > > [*Mankind has injected a colossal pulse of CO2 in the atmosphere, which > continues to grow, and will continue to grow under any Copenhagen > agreement. Global warming is an inevitable consequence of the excess CO2 > (although other gases contribute, both positively and negatively).*] > > Nobody wanted to point out that, at this speed, the bus would become > unstable and almost certainly crash off the road putting everybody's life at > risk. Thus it was actually in everybody's interest to close the throttle > and apply the brakes straight away. The compromise they had reached just > gave a false sense of security. > > [*Nobody seems willing to point out that our present path, akin to > business as usual, could lead to the collapse of our civilisation, e.g. > through famine. Any deal at Copenhagen is liable to engender a false sense > of security.*] > > Soon after the compromise had been reached, the bus, already travelling > dangerously fast, skidded on some ice, which the driver saw too late, hit a > tree and burst into flames, killing all on board. > > [*Tipping points have been ignored. The Arctic sea ice could disappear > quite rapidly, with potentially lethal consequences from methane release > and/or Greenland ice sheet disintegration. The Amazon rainforest is also at > risk of drought, leading to die off and burn.*] > > Sadly this fate was not inevitable. Unknown to the driver, there were > emergency brakes that could have slowed the bus, even while the throttle was > open. But the driver had been told that these emergency brakes were too > dangerous to use, so was not prepared to use them. When he saw the ice, he > tried to apply the emergency brakes but it was too late. > > [*The only reasonable chance of saving the Arctic sea ice is through the > application of geoengineering to cool the region. The chance of > geoengineering successfully diminishes as positive feedbacks build up in the > Arctic. The more we delay geoengineering, the more we risk passing a point > of no return, so that a gruesome fate becomes inevitable, possibly even for > most people alive today.*] > > Cheers, > > John > > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<geoengineering%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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