James Annan wrote:
> AdamW wrote:
>> Phil Hays wrote:
> >> Isn't there also the "Snowball Earth" state switch? Both to the
> >> "frozen death" state, and back again after enough CO2 accumulates?
> > Isn't that dependant on the ice-albedo feedback, which is excluded
> > from climate sensitivity?
> Sea ice and snow cover are both counted, which probably could achieve
> the same end. But that's a long way from the present day situation. IIRC
> someone on RC said that they thought a venus-like runaway was
> impossible, but I'm not sure what basis that had.
Sea ice would be required, for if the oceans don't freeze we don't
match the geologic record of such events ~700 million years ago.
Nearly complete sea ice coverage for many thousands of years is
indicated by the presence of "BIF's" or Banded Iron Formations.
"Snowball Earth" is not as far away from the current climate as we are
likely to change the climate, however in the other direction. Taking
a doubling of CO2 as a unit of measure, roughly two halvings of CO2
from pre-industrial. We are moving the other way, so this isn't much
of a concern for us, except for one point. Last I heard, current
climate models can't reproduce these events, unlike older climate
models. The models do produce a substantial non-linearity, but the
cooling stops well before the ocean has completely frozen. Has this
changed, or in other words does one or more of the modern models
reproduce these events? What about the models you work with?
--
Phil Hays
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