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Re: Under a Green Sky
The Greenland Icecap is not going to melt in a few hundred years. It takes
much longer. At the end of the last glaciation 11600 years ago climate in
northern Europa became as warm or warmer than today and much drier, but
even so it took 2000 years for the residual Scandinavian icecap to melt,
even though it could calve into the Bothnian Gulf for much of the time.
The only way an icecap can melt fast is if it can calve out into the sea.
The Greenland icecap can't since its bed is above sealevel. Note that not
even the southern dome of the Greenland icecap melted during the previous
(Eemian) interglacial when arctic temperatures were about 6 degrees
centigrade warmer than now.
Are you sure they were that much warmer? The following "brief communication"
says that when the annual average temperature in Greenland increases by more
than 2.7 °C (which is going to happen according to most of the scenarios of
the IPCC report of 2001 -- the latest one is said to have generally warmer
scenarios), melting exceeds snowfall, so that "the ice-sheet must contract,
even if iceberg production is reduced to zero as it retreats from the
coast", which is estimated to take at least about 1,000 years. Don't the
huge amounts of meltwater produced every summer flow into the sea? It does
in West Antarctica:
Jonathan M. Gregory, Philippe Huybrechts & Sarah C. B. Raper: Threatened
loss of the Greenland ice sheet, Nature 428, 616 (8 April 2004)
Unfortunately, the citation for the 2.7 °C is a paper from 1991...
More recent papers -- which I have been too stupid to save, and here I don't
have full-text Science access (in the lab I have, but the public transport
is on strike) -- find that the ice sheet is melting faster than expected
under any of the scenarios considered above, and emphasize that, in
interglacials, it depends on itself to survive by creating its own cold
weather around itself: if it is removed from a climate model even under
preindustrial CO2 levels, it doesn't come back. At least one of these papers
says the ice sheet will likely be gone in a few hundred years.
However, searching for papers with "Greenland" in the title on the Science
website brings up almost only papers on the melting of the ice-sheet. Here's
one http://www.sciencemag.org/cgi/content/abstract/311/5768/1751 that
simulates the conditions of the last interglacial and correctly concludes
that the ice-sheet did not melt completely, even though the sea level did
rise several meters above today's. Here's another
http://www.sciencemag.org/cgi/content/abstract/sci;311/5768/1747 which looks
at the last interglacial and whose abstract ends in: "The record of past
ice-sheet melting indicates that the rate of future melting and related
sea-level rise could be faster than widely thought." Some
http://www.sciencemag.org/cgi/content/summary/sci;315/5818/1508 also worry
that "Satellite data show that ice sheets can change much faster than
commonly appreciated, with potentially worrying implications for their
This paper http://ppg.sagepub.com/cgi/reprint/30/6/785, which is freely
accessible, mentions the recent increase in Greenland melting:
"Alternative observational data provided by´radar interferometry suggests
that, while the interior of the Greenland ice sheet is in approximate mass
balance, there is rapid thinning around the periphery close to certain
outlet glaciers (Rignot and Kanagaratnam, 2006). Many of these glaciers have
accelerated, increasing Greenland's estimated contributionto sea-level rise
from 0.23 +- 0.08 mm/yr in 1996 to 0.57 +- 0.1 mm/yr in 2005. This
acceleration is also recorded by increased glacial seismicity (Ekström et
al., 2006). Interestingly, these data are strongly seasonal, with seismicity
increasing nearly fivefold during the summer months. This may indicate
accelerations are linked to bed lubrication by increased meltwater
penetration, suggesting that even modest changes in temperature (~1°C) can
produce large changes in discharge (Zwally et al., 2002; Joughin, 2006)."
"This variability poses new challenges to existing conceptual and
mathematical models of how sea-level/cryosphere/climate linkages operate
during warm intervals, both at the suborbital (millennial) and subdecadal
timescales. For example, the recent changes in Greenland revealed by seismic
and satellite data cannot be explained by melting mechanisms alone (Rignot
and Kanagaratnam, 2006). The physical processes associated with dynamic
glacier change, perhaps linked to ocean warming and the retreat of tidewater
glaciers (Joughin et al., 2004; Alley et al., 2005; Payne et al., 2004;
Bindschadler, 2006), are not included in the current models used to predict
future sea-level contributions (Marshall, 2005). Consequently, these models
do not display the sensitivity to change indicated by recent remote sensing
data and may underestimate the magnitude of future sea-level rise
(Dowdeswell, 2006; Rignot and Kanagaratnam, 2006; Velicogna and Wahr, 2006).
This is particularly interesting in light of a recent modelling study that
proposes existing contributions from mountain glaciers and ice caps may have
been overestimated (Raper and Braithwaite, 2006)."
"An alternative is to examine records from previous interglacials, which
provide a longer-term context against which more recent changes can be
assessed. The last interglacial (LIG) has attracted particular attention as
Arctic temperatures were warmer, sea levels higher and the Greenland Ice
sheet smaller than present. For example, Overpeck et al. (2006) use a
coupled ocean-atmosphere climate model to simulate LIG climate and compare
this with simulations of the next 140 years to examine potential ice-sheet
contributions to sea-level rise. Their results suggest that by 2100 the
Greenland region will be at least as warm as it was during the LIG and, by
implication, warm enough to melt large portions of the Greenland Ice Sheet."
Overpeck et al. (2006) is the first paper to which I provide a link above.
Lastly, there's this paper
http://www.sciencemag.org/cgi/content/abstract/313/5795/1958 which reports a
high probability for "accelerated melting since the summer of 2004".
I give up here, this off-topic post is long enough...!
As for MIS 11 (Holstein) when the Greenland ice and at least part of
the West Antarctic ice melted, the worrying thing about is that it
was apparently NOT an extremely warm interglacial.
Does this hold for the whole interglacial, or only for the earlier part?
IIRC the sea-level highstand came late in the interglacial.
Concerning Bangladesh, that country will be gone in a few centuries,
climate warming or not. The Ganges and Brahmaputra are dammed now,
little sediment therefore comes into the delta and the sea is going
to erode it away pretty quickly. The same thing is happening to the
Nile Delta since the Assuan dam was built.
> > Right now, the current state of the climate follows suit as it
> > warms from its recent glacial state.
> Ouch!!! This is nonsense. The _end of_ the last ice age is over, and
> has been over for 11,000 years.
We still have glaciers. We still have ice caps. I didn't say Ice Age. I
said glacial state. Ouch!!!
I've never seen "glacial state" used like this, and because there's no real
chance that East Antarctica will become ice-free, I didn't get the idea that
you may have meant the article was talking about an exit from the current
"icehouse" state and the return of the middle Eocene and earlier
"greenhouse" state. So, while wrong, my unfortunate knee-jerk reaction was
inevitable, and further increased by the fact that I've several times come
across the supposed argument (elsewhere on the Internet) that the current
warming is still part of the end of the last ice-age.