[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Under a Green Sky

" The Greenland Icecap is not going to melt in a few hundred years. It
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..."

I am not sure how this played out in reality, but it is theoretically, if 
counter-intuitively, possible for wetter, cooler summers to melt ice much 
faster than warmer dry ones. This is because evaporative cooling is increased 
in a condition of low relative humidity, and snow/ice has high albedo. In other 
words, the thin layer of ice melted by sunshine evaporates rapidly, cooling the 
ice below; whereas rain transmits heat to the icepack without significant 
evaporation taking place. This could be exacerbated where summer air is dry, 
and most precipitation occurs in winter (slow melting), or where summer air is 
wet and most precip occurs in summer (fast melting). As a meteorological 
phenomenon, familiar to those who shovel snow.


----- Original Message ----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Sent: Monday, November 19, 2007 8:35:54 AM
Subject: Re: Under a Green Sky

> The Greenland Icecap is not going to melt in a few hundred years. It
> 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,
> even so it took 2000 years for the residual Scandinavian icecap to
> even though it could calve into the Bothnian Gulf for much of the
> The only way an icecap can melt fast is if it can calve out into the
> The Greenland icecap can't since its bed is above sealevel. Note that
> even the southern dome of the Greenland icecap melted during the
> (Eemian) interglacial when arctic temperatures were about 6 degrees 
> centigrade warmer than now.

Are you sure they were that much warmer? The following "brief
says that when the annual average temperature in Greenland increases by
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
scenarios), melting exceeds snowfall, so that "the ice-sheet must
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
huge amounts of meltwater produced every summer flow into the sea? It
in West Antarctica: 

Jonathan M. Gregory, Philippe Huybrechts & Sarah C. B. Raper:
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
have full-text Science access (in the lab I have, but the public
is on strike) -- find that the ice sheet is melting faster than
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
says the ice sheet will likely be gone in a few hundred years.

However, searching for papers with "Greenland" in the title on the
website brings up almost only papers on the melting of the ice-sheet.
one http://www.sciencemag.org/cgi/content/abstract/311/5768/1751 that 
simulates the conditions of the last interglacial and correctly
that the ice-sheet did not melt completely, even though the sea level
rise several meters above today's. Here's another 
http://www.sciencemag.org/cgi/content/abstract/sci;311/5768/1747 which
at the last interglacial and whose abstract ends in: "The record of
ice-sheet melting indicates that the rate of future melting and related
sea-level rise could be faster than widely thought." Some 
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
that, while the interior of the Greenland ice sheet is in approximate
balance, there is rapid thinning around the periphery close to certain 
outlet glaciers (Rignot and Kanagaratnam, 2006). Many of these glaciers
accelerated, increasing Greenland's estimated contributionto sea-level
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
al., 2006). Interestingly, these data are strongly seasonal, with
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)
produce large changes in discharge (Zwally et al., 2002; Joughin,

"This variability poses new challenges to existing conceptual and 
mathematical models of how sea-level/cryosphere/climate linkages
during warm intervals, both at the suborbital (millennial) and
timescales. For example, the recent changes in Greenland revealed by
and satellite data cannot be explained by melting mechanisms alone
and Kanagaratnam, 2006). The physical processes associated with dynamic
glacier change, perhaps linked to ocean warming and the retreat of
glaciers (Joughin et al., 2004; Alley et al., 2005; Payne et al., 2004;
Bindschadler, 2006), are not included in the current models used to
future sea-level contributions (Marshall, 2005). Consequently, these
do not display the sensitivity to change indicated by recent remote
data and may underestimate the magnitude of future sea-level rise 
(Dowdeswell, 2006; Rignot and Kanagaratnam, 2006; Velicogna and Wahr,
This is particularly interesting in light of a recent modelling study
proposes existing contributions from mountain glaciers and ice caps may
been overestimated (Raper and Braithwaite, 2006)."

"An alternative is to examine records from previous interglacials,
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
sheet smaller than present. For example, Overpeck et al. (2006) use a 
coupled ocean-atmosphere climate model to simulate LIG climate and
this with simulations of the next 140 years to examine potential
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,
implication, warm enough to melt large portions of the Greenland Ice

Overpeck et al. (2006) is the first paper to which I provide a link

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
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 Ass


> > > 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,
> > has been over for 11,000 years.
> We still have glaciers. We still have ice caps. I didn't say Ice Age.
> said glacial state. Ouch!!!

I've never seen "glacial state" used like this, and because there's no
chance that East Antarctica will become ice-free, I didn't get the idea
you may have meant the article was talking about an exit from the
"icehouse" state and the return of the middle Eocene and earlier 
"greenhouse" state. So, while wrong, my unfortunate knee-jerk reaction
inevitable, and further increased by the fact that I've several times
across the supposed argument (elsewhere on the Internet) that the
warming is still part of the end of the last ice-age.