> We are not talking about a "little" warming at least in
> terms of the rate of change as compared with natural events. Even the
> absolute change is strikingly large in the AR4 assessment's 2100 map.
It is little when expressed as say, equivalent kilometers you'd need
to move towards the equator (2-3C is about 400-600 km), and when
implying that it might mean relatively little else of consequence.
2-3C as compared with probably +/-1C kind of stability over the last
10000 years or so, now that isn't little, particularly while thinking
that the impact on humanity might be major.
I accept that 2-3C over a 100 years is climate historically speaking
an abrupt change, and of course many other things have been changing
abruptly (land use, aerosols, but also the number of nuclear weapons
on the planet say), which may synergistically make things worse. On
the other hand, climate change might counteract them.
> Perhaps other phenomena lurk.
Including ones where climate change might be precisely what would
prevent a "catastrophe"?
> A good deal of
> research money is indded shifting toward this question.
Good to hear that.
> There's also a philosophical question of whether it is reasonable to commit
> to a 500 year time scale of huge coastal flooding if it might still be
> avoided.
I am not sure what is meant by "commit" and "might still be avoided"
here. It makes me think of "tipping points" and irreversibilities.
Maybe by 2100 after having blown past 600 ppm, even reducing CO2 back
to 300 ppm by 2200 would still mean 5 m by 2500, assuming nothing else
is done between 2200 and 2500 (say local albedo enhancement or
whatever). I accept it's possible that going to 300 ppm by 2200
mightn't be enough to reverse the "commitment", or that given the
right apocalyptic scenario for societal breakdown from nuclear war,
terrorism, the end of cheap oil, whatever, we mightn't have the
resources to get to 300 ppm by 2200 after having been above 600 ppm in
2100.
But my philosophical viewpoint there is not to worry about 5 m by
2500, it'll either not happen, because we reverse the commitment, or
society will have other more pressing issues to worry about, and 5 m
over a few hundred years is a lot more easily adapted to than 5 m in
50 years, even assuming societal breakdown, the end of economic growth
and Bangladesh getting poorer rather than richer between now and 2500.
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