Originally posted by shunyadragon
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The human impact is a spanner in the works; the long range impact of an enhanced greenhouse effect is very likely to have prevented the next ice age from occurring at all, even if we manage to put strong limits on future emissions and limit the consequent extent of warming over the next century. If we overheat the planet in a big way by continuing to burn as much fossil carbon as we can, then the whole ice age cycle thing is likely to stop for quite a long time; maybe several hundred thousand years.
In brief: long range estimation of a perturbed climate indicate that the usual triggers for the next ice age won't be enough; we've ALREADY prevented the next ice age. This long range isn't a long range climate projection as such; it's a long range CO2 projection (which is on much more solid quantified grounds.) Since raised CO2 levels persist for a long time, they become a factor to compare with the orbital forcings thought to precipitate ice ages. If CO2 levels are significant raised, a glacial epoch can't get started.
Typically, discussions of global warming and human driven climate change focus on the next 100 years. The impact of a changed atmosphere lasts much much longer than this.
A good book on this is Deep Future, by Curt Stager (2011). Subtitled: "The next 100,000 years of life on Earth". Online resources include This review at Science magazine, and Stager, C. (2012) What Happens AFTER Global Warming? in Nature Education Knowledge 3(10):7
Originally posted by Jedidiah
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However, as noted, the "something drastic" has already happened, and glacial cycles have most likely had a hiccup for the next hundred thousand years, at least.
You do touch on a very interesting point, however!
Solar changes have their impact on a scale of more like 100 million years; and it has been a mystery as to why Earth's climate has been so comparatively stable on such scales with the Sun getting brighter all the time. This is called the "faint young sun paradox". Google it; it's a well known puzzle in science.
The answer turns out to be carbon dioxide again; carbon dioxide levels in the atmosphere have fallen as the Sun has got brighter, and so the two factors (roughly) cancel out. There's a fairly well supported hypothesis about this phenomenon. Specifically, that this is no accident, but is rather the consequence of a very long range "slow" negative feedback. Hotter temperatures tend to result in increased weathering, and a draw down of carbon from the atmosphere to carbonates into geological reserves. The specifics mean that there is a characteristic temperature at which the draw down matches the comparatively steady output of carbon dioxide again from geological carbonate reserves through volcanic activity; and the feedback tends to drive temperature towards that sweet point, for a whole range of very different solar inputs. The effect is really really slow however. It's enough to keep up with the slow rate of increased solar output, but not enough to be a big factor driving swings in climate as occur from time to time for many reasons.
Cheers -- sylas
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