Dear Peter,
As I continue to try to work out what forces we are up against, in
readiness for the London October 15-16 Arctic methane workshop, I am
struck by how much less we understand about what is going on in the
Arctic than we understand about the rather straight-forward
engineering/geoengineering techniques that might be used to releave the
situation. Much is touted about the uncertainties and dangers of
geoengineering but it seems to me that the uncertainties and dangers of
the Arctic future without geoengineering are far greater.
There is almost no precident for what we can see happening, except
perhaps for the end of the Eemian warming. In this article here [1] it
is implied that the sea ice might have retreated as far as having an ice
free period in summer around 7000 yrs ago. But is there evidence of
such a retreat since the Younger Dryas cold period ended, about 10,000
years ago?
In a related article [2] they are now talking about seasonally ice free
by 2020, but still ignoring the PIOMAS model, whose exponential trend
gives this date as 2015 [3]. Nevertheless, the 2020 date must be a real
shock to Greenpeace. One wonders whether their sea ice measurements
will back up PIOMAS. Do you know the people involved? There is a
student from Cambridge, I note ("Cambridge University PhD student Till
Wagner").
In [2] there point to one effect of sea ice retreat: "If the Arctic
Ocean were open sea in autumn, without an insulating layer of ice, that
would allow more warming of the polar air." However there are three
other effects, that one needs to try to quantify:
1) the extra thermal radiation into space as open water radiates far
more effectively than ice, partly because it's a few degrees warmer but
also because the ice is insulating;
2) the extra water vapour, which is a powerful greenhouse gas;
3) the extra precipitation from this water vapour, which can fall as
snow to increase albedo.
Do you have any idea of the quantities of heat-fluxes involved?
I assume that the albedo change/flip is taken into account in modelling,
but are these other factors? (I'm copying to Ken Caldeira and others for
comment.)
On top of this, we have the possibility of a major movement of fresh
water to cause an interruption of AMOC. Is there any recent evidence to
suggest this might happen or not, with timescale/probability?
Thanks,
John
[1] http://planetark.org/wen/63200
[2] http://planetark.org/wen/63201
[3] http://neven1.typepad.com/blog/2011/06/piomas-version-2.html (see
bottom graph)
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