Re: [asa] Arctic melt worse than predictions

From: Rich Blinne <rich.blinne@gmail.com>
Date: Thu May 03 2007 - 09:24:14 EDT

Predicting glaciers is hard like predicting earthquakes and for
similar reasons. Think of the interface between the ground and the
glacier like an earthquake fault. The ground grips the glacier in a
very non-linear fashion and it very dependent on the topology of the
ground. Add the complicating factor of "lubrication" of the water
under the glacier caused by global warming. This can cause the
possibility of a catastrophic failure and we have observed such
phenomenon recently in both Greenland and Antarctica. Thus human-
induced climate change has made an easy-to-model slow movement of
glaciers into a difficult-to-model chaotic one. Is it likely that the
"big one" will happen in the near (geological) future? Yes. Will it
happen tomorrow? Don't have a clue. In the same way, is it likely
that we get 10s of meters of sea level rise from catastrophic ice
failure in the next few centuries if we continue along business as
usual? Yes. Will it happen before 2100? Don't have a clue and neither
do the glaciologists. Note the recently-released technical summary of
the IPCC that didn't get manipulated by the politicians:

> The palaeo-record of previous ice ages indicates that ice sheets
> shrink in response to warming and grow in response
> to cooling, and that shrinkage can be far faster than growth. The
> volumes of the Greenland and Antarctic Ice Sheets are
> equivalent to approximately 7 m and 57 m of sea level rise,
> respectively. Palaeoclimatic data indicate that substantial
> melting of one or both ice sheets has likely occurred in the past.
> However, ice core data show that neither ice sheet was
> completely removed during warm periods of at least the past million
> years. Ice sheets can respond to environmental forcing
> over very long time scales, implying that commitments to future
> changes may result from current warming. For example,
> a surface warming may take more than 10,000 years to penetrate to
> the bed and change temperatures there. Ice velocity
> over most of an ice sheet changes slowly in response to changes in
> the ice sheet shape or surface temperature, but large
> velocity changes may occur rapidly in ice streams and outlet
> glaciers in response to changing basal conditions, penetration
> of surface melt water to the bed or changes in the ice shelves into
> which they flow. {4.6, 6.4}
> Models currently configured for long integrations remain most
> reliable in their treatment of surface accumulation
> and ablation, as for the TAR, but do not include full treatments of
> ice dynamics; thus, analyses of past changes or future
> projections using such models may underestimate ice flow
> contributions to sea level rise, but the magnitude of such an
> effect is unknown. {8.2}

On May 3, 2007, at 6:40 AM, Dave Wallace wrote:

> Jim Armstrong wrote:
>> There were also these two headlines.
>> Nothin's simple.
>> JimA
>> Kilimanjaro's Glaciers May Last Longer Than Predicted <http://
>> news.nationalgeographic.com/news/2007/05/070501-kilimanjaro.html>
>> The First Refugees of Global Warming <http://www.redorbit.com/news/
>> science/921961/the_first_refugees_of_global_warming/index.html>__
>
> Yup I saw both of those headlines as well and agree the the
> evidence is not simple. As you may remember I have concerns about
> the models too.
>
> Dave W
>
>
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Received on Thu May 3 09:24:54 2007

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