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

Re: Under a Green Sky

> > 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. <<

I should have mentioned Antarctica, but was under the assumption that it's a given understanding that the continent will most likely never be ice-free. I should know by now what happens when you assume....

Kris
Saurierlagen@gmail.com

-----Original Message-----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Sent: Mon, 19 Nov 2007 5:35 am
Subject: 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 ÂC (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: http://www.sciencemag.org/cgi/content/abstract/sci;315/5818/1544.

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 ÂC 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 stability"...

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 byÂradar 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 (EkstrÃm 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 (~1ÂC) 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.


Good point.

------------------------

> > 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.


Kris
Saurierlagen@gmail.com


-----Original Message-----
From: David Marjanovic <david.marjanovic@gmx.at>
To: DML <dinosaur@usc.edu>
Sent: Mon, 19 Nov 2007 5:35 am
Subject: 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.Â
Â
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 ÂC (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: http://www.sciencemag.org/cgi/content/abstract/sci;315/5818/1544.Â;
Â
Jonathan M. Gregory, Philippe Huybrechts & Sarah C. B. Raper: Threatened loss of the Greenland ice sheet, Nature 428, 616 (8 April 2004)Â
Â
Unfortunately, the citation for the 2.7 ÂC is a paper from 1991...Â
Â
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.Â
Â
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 stability"...Â
Â
This paper http://ppg.sagepub.com/cgi/reprint/30/6/785, which is freely accessible, mentions the recent increase in Greenland melting:Â
Â
"Alternative observational data provided byÂradar 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 (EkstrÃm 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 (~1ÂC) can produce large changes in discharge (Zwally et al., 2002; Joughin, 2006)."Â
Â
"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)."Â
Â
"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."Â
Â
Overpeck et al. (2006) is the first paper to which I provide a link above.Â
Â
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".Â
Â
I give up here, this off-topic post is long enough...!Â
 
As for MIS 11 (Holstein) when the Greenland ice and at least part ofÂ
the West Antarctic ice melted, the worrying thing about is that itÂ
was apparently NOT an extremely warm interglacial.Â
Â
Does this hold for the whole interglacial, or only for the earlier part? IIRC the sea-level highstand came late in the interglacial.Â
 
Concerning Bangladesh, that country will be gone in a few centuries,Â
climate warming or not. The Ganges and Brahmaputra are dammed now,Â
little sediment therefore comes into the delta and the sea is goingÂ
to erode it away pretty quickly. The same thing is happening to theÂ
Nile Delta since the Assuan dam was built.Â

Â
Good point.Â
Â
------------------------Â
Â
> > Right now, the current state of the climate follows suit as itÂ
> > warms from its recent glacial state.Â
>Â
> Ouch!!! This is nonsense. The _end of_ the last ice age is over,
andÂ
> has been over for 11,000 years.Â
Â
We still have glaciers. We still have ice caps. I didn't say Ice Age.
IÂ
said glacial state. Ouch!!!Â
Â
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. Â


________________________________________________________________________
Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com