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ARGeezer:
To me a one meter+ rise is quite conceivable, and perhaps likely, over a forty year period.

And Patrice seems to suggest he is as pessimistic about this. What are your reasons/thoughts behind this?

I ask because there are at least two groups that I know which do not think this is likely. The first the AR4 from the IPCC, the second the Dutch water boards. My uncle used to work for the latter, and the consensus remains that for 2100 the Netherlands will not face a 1 meter rise of sea level.

Granted, I'm one of the first to say that in climate change we don't know what we don't know, and a lot uncertainty remains, but on what is this pessimism based?

by Nomad on Sun May 24th, 2009 at 08:13:07 AM EST
[ Parent ]
radiative output (6% in some wavelenghts, it is claimed!)
Sun has got to be worshipping coal and Pluto.
Absent this solar silliness (demonstrated by fewer sunspots in a century), I gave the reasons  above for a considerable sea rise.

Moreover, upon warming I see a reason for the EAST Antarctic basins to melt. They front the sea at the polar circle (i.e., way far from the pole).

I will put all this together in a post on patriceayme.wordpress.com... But I can't believe the sun... Will not save us, because if the CO2 keeps on going up, the oceans will turn into diluted lemon juice...
PA

Patrice Ayme Patriceayme.com Patriceayme.wordpress.com http://tyranosopher.blogspot.com/

by Patrice Ayme on Sun May 24th, 2009 at 10:47:43 AM EST
[ Parent ]
but on what is this pessimism based?

In my case, I am pessimistic that we, as a species, will be able to act with sufficient alacrity to avert ambient temperature increases of 2-4C, or possibly more.  The collective reporting I have seen on the Greenland and West Antarctic Ice Sheets, combined with what I have read about the probable rapid rate of melting of the North American Ice Sheet at the beginning of our current epoch, leads me to doubt that extrapolations of melt rates for these ice sheets will follow current linear models.  

I fear current models assume that the ice sheets will melt in place and perhaps the rate of calving of icebergs into the ocean will increase at about the rate of increase we have recently observed.  Were you able to inform me otherwise I would be relieved.  I am concerned that recent reports of melt water toward the center of these ice sheets creating channels to bedrock will increase and will increase the rate of motion in second order or higher ways.

I think it is more likely that we will document accelerating  processes at work within a decade or so than that we will confirm existing models.  I have no way of knowing how fast melting will occur, but a one meter rise seems much more likely to me than a 10cm rise by mid-century.  I am also concerned that responsible and competent authorities are not creating models that are based on accelerating melt rates and ice movement and using them to evaluate which model best fits observation.  If they are and if they have published results, I have missed the report.

We have all deplored the extent to which Bush era science was subjected to political censorship.  But I do not think that this problem has vanished with the change of one administration in one country.  Nor do I think that current estimates err on the side of pessimism.  To me the question is how much less optimistic should we be.  

"It is not necessary to have hope in order to persevere."

by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Sun May 24th, 2009 at 01:03:24 PM EST
[ Parent ]
who is saying what. Sun seems confused too. I gave above new reasoning for 25 meter rise. But if the sun slows down seriously, that's out of the window, we will know soon. I will put things in an essay, to kill time before my next publication of Qur'an selects...
;-)!

Patrice Ayme Patriceayme.com Patriceayme.wordpress.com http://tyranosopher.blogspot.com/
by Patrice Ayme on Mon May 25th, 2009 at 02:28:18 AM EST
[ Parent ]
I'm pessimistic because I suspect that the ice shelves are being modelled as more stable and warming-resistant than they really are. A while ago I wrote:
A lot of the climate models seem to have modelled the ice sheets as ice cubes when they behave more like a drop of honey. Ice cubes are very poor heat conductors, insulate their own interior, and only melt on the surface. A drop of honey gets less viscous and flows more easily as it warms up. But I am not an expert on climate modelling.
ARGeezer:replied with
Lately I have been reading articles in Science News and elsewhere about glacial lakes melting holes through very thick glaciers and disappearing through said holes. It appears that this additional water further lubricates the interface between the ice and the rock below, increasing the rate of glacier flow.
I was recalling an article we had discussed in the Salon a couple of years back where some climate scientists suggested that the "ice cube" model used in climate simulations led to melting times of the order of 1,000 years whereas the actual dynamics of the ice shelf might lead it to disintegrate on much shorter timescales.

Then I have seen footage of how meltwater pours into deep crevasses in the Antarctiva ice sheet, going directly to the bedrock where it lubricates the interface between the ice and the rock. I am not convinced large chunks of the Antactica ice cap couldn't simply slide into the sea as a result of this lubrication.

The brainless should not be in banking. — Willem Buitler

by Migeru (migeru at eurotrib dot com) on Mon May 25th, 2009 at 06:32:49 AM EST
[ Parent ]
of the geologist, I think that's too pessimist. For now. Don't understand me wrong, if global temperatures creep up another 2 degrees, we are in deep serious - which is why business-as-usual GHG emissions cannot hold.

A few responses up, nanne actually links to one of the articles that illustrate the point, namely:

  1. as far as has been determined, current global temperature is still cooler than the Holocene climatic optimum - particularly in the northern hemisphere.

  2. the last interglacial period (prior to this one) did have 4 - 6 meters higher sea level - but temperatures were an estimated 2 degrees higher. See here and here for examples I've found quickly.

Looking at temperature correlations, we may be seeing calving reaching a new equilibrium and grow constant but on the condition that temperatures stablise.
by Nomad on Mon May 25th, 2009 at 09:52:25 AM EST
[ Parent ]
Nomad:
Don't understand me wrong, if global temperatures creep up another 2 degrees, we are in deep serious - which is why business-as-usual GHG emissions cannot hold.
On that note:



The brainless should not be in banking. — Willem Buitler

by Migeru (migeru at eurotrib dot com) on Tue May 26th, 2009 at 04:12:27 AM EST
[ Parent ]
are still something else: bottom is below sea level. Way below. my hunch is that if ocean temps get above a threshold, the WAIS will disintegrate instantaneously.

Patrice Ayme Patriceayme.com Patriceayme.wordpress.com http://tyranosopher.blogspot.com/
by Patrice Ayme on Tue May 26th, 2009 at 07:46:59 PM EST
[ Parent ]

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