Re: [asa] Effect of CO2-Induced Global Warming on Antarctic Surface Mass Balance a Hundred Years Hence

To those unfamiliar with the topic of global warming and ice-sheet
contributions, these findings may appear shocking. However, science
already knows that

<quote>Antarctica contributes negatively to sea level on account of
increased accumulation, while Greenland contributes positively
because ablation increases more rapidly. </quote>

In addition, ice sheet contributions have since long been considered
to contribute only in minor ways to sea level increases.
Contributions of glaciers and ice caps are thought to be of far more
relevance, even though they are smaller in extent.

The AR4 draft reports mentions

The most important cryospheric contributions to sea level variations
arise from changes of the ice on land, e.g., glaciers, ice caps, and
ice sheets. In the TAR recent ice contribution was estimated as
0.2–0.4 mm/yr (of 1–2 mm/yr total sea level rise). New results
presented here indicate that all glaciers contributed about 0.51±0.32
mm/yr during 1963–2003, increasing to 0.81 ± 0.43 from 1993–2003
(Table 4.5.2). Estimates of both ice sheets combined provided a
contribution ranging from –0.35 to +0.72 for 1961–2003 and 0 to 0.8
mm/year through 1993–2003, increasing during this period. A
conservative error estimate in terms of summing ranges is given in
Table 4.8.1. Assuming a midpoint-mean, interpreting the range as
uncertainty, and using Gaussian error summation of estimates for
glaciers and ice sheets, suggests that the total ice contribution to
sea level rise during 1993 to 2003 was approximately 1.2 ± 0.6 mm/yr.

        Sea Level Equivalent (mm/yr)
1961–2003 1993–2003

Glaciers and ice caps +0.19 to +0.83 +0.38 to +1.24
Greenland −0.07 to +0.17 +0.14 to +0.28
Antartica −0.28 to +0.55 −0.14 to +0.55
Total −0.16 to +1.55 +0.38 to +2.07

Hope this clarifies these truly complex issues in a manner suitable
for wider consumption.

Oh yes, before I forget

<quote>The IPCC4 estimated a zero Antarctic contribution to sea-level
rise over the past century, and projected a small negative (about -1
cm) contribution for the twenty-first century. The latter estimate
reflects a negative contribution to sea-level rise due to increased
ice accumulation and an arbitrary, positive contribution (0.1–0.4 mm
yr-1) due to hypothetical WAIS instability. </quote>

http://www.nature.com/nature/journal/v393/n6683/full/393325a0.html

Seems that some are fighting a strawman here as the IPCC has taken
into account a small negative contribution of antartic contributions
to sea level rise.

Hope this helps

<quote>Using a three-dimensional thermomechanical ice-sheet model,
Huybrechts & De Wolde (1999) found the ice-dynamic and topographic
response to contemporary mass-balance perturbations to be negligible
for Antarctica and small for Greenland for the twentieth and
twenty-first centuries</quote>

I can understand that those unfamiliar with the science would be
tempted to come to conclusions that the issue of sea level rise is
contradicted by science, when in fact, the report validates that which
science already knew.

hence the conclusion

<quote>argue strongly against climate-alarmist predictions of future
catastrophic sea level rise due to the mass wastage of the Antarctic
Ice Sheet caused by CO2 -induced global warming.</quote>

seems to be nothing more than a red herring and strawman.

On 2/4/07, Janice Matchett <janmatch@earthlink.net> wrote:
>
> "I don't trust ANYBODY's predictions on sea level. There are two many free
> variables most specifically how much anthropogenic CO2 there is going to be.
> The climate sensitivity numbers from the 2001 report have been confirmed by
> more recent research. We don't know how successful or unsuccessful we will
> be at controlling CO2 emissions or external factors such as possibly running
> out oil might have. We are discovering different negative (and positive!)
> feedback mechanisms that also affect the CO2 levels. Since 2001 we have
> better models where given the right inputs we can predict the effects but it
> is still GIGO (garbage in garbage out) because we still do not have accurate
> prediction of CO2 levels and probably never will." ~ Rich Blinne Mon, 11 Dec
> 2006 11:49:39 -0700
>
> ~ Janice :)
>
> Effect of CO2 -Induced Global Warming on Antarctic Surface Mass Balance a
> Hundred Years Hence
>
> Reference
> Krinner, G., Magand, O., Simmonds, I., Genthon, C. and Dufresne, J.-L.
> 2007. Simulated Antarctic precipitation and surface mass balance at the end
> of the twentieth and twenty-first centuries. Climate Dynamics 28: 215-230.
>
> What was done
> The authors used the LMDZ4 atmospheric general circulation model (Hourdin
> et al., 2006) to simulate Antarctic climate for the periods 1981-2000 (to
> test the model's ability to adequately simulate present conditions) and
> 2081-2100 (to see what the future might hold for the mass balance of the
> Antarctic Ice Sheet and its impact on global sea level).
>
> What was learned
> Krinner et al. report, first of all, that "the simulated present-day
> surface mass balance is skilful on continental scales," giving them
> confidence that their results for the end of the 21st century would be
> reasonably skilful as well. Of that latter period a full century from now,
> they determined that "the simulated Antarctic surface mass balance increases
> by 32 mm water equivalent per year," which corresponds "to a sea level
> decrease of 1.2 mm per year by the end of the twenty-first century," which
> would in turn "lead to a cumulated sea level decrease of about 6 cm." This
> result, in their words, occurs because the simulated temperature increase
> "leads to an increased moisture transport towards the interior of the
> continent because of the higher moisture holding capacity of warmer air,"
> where the extra moisture falls as precipitation, causing the continent's ice
> sheet to grow.
>
> What it means
> The results of this study - based on sea surface boundary conditions taken
> from IPCC 4th assessment report simulations (Dufresne et al., 2005) that
> were carried out with the IPSL-CM4 coupled atmosphere-ocean general
> circulation model (Marti et al., 2005), of which the LMDZ4 model is the
> atmospheric component - argue strongly against climate-alarmist predictions
> of future catastrophic sea level rise due to the mass wastage of the
> Antarctic Ice Sheet caused by CO2 -induced global warming. In fact, they
> suggest just the opposite, i.e., that CO2 -induced global warming would tend
> to buffer the planet against such an outcome.
>
> References
> Dufresne, J.L., Quaas, J., Boucher, O., Denvil, S. and Fairhead, L. 2005.
> Contrasts in the effects on climate of anthropogenic sulfate aerosols
> between the 20th and the 21st century. Geophysical Research Letters 32:
> 10.1029/2005GL023619.
>
> Hourdin, F., Musat, I., Bony, S., Braconnot, P., Codron, F., Dufresne,
> J.L., Fairhead, L., Filiberti, M.A., Friedlingstein, P., Grandpeix, J.Y.,
> Krinner, G., Le Van, P., Li, Z.X. and Lott, F. 2006. The LMDZ4 general
> circulation model: climate performance and sensitivity to parameterized
> physics with emphasis on tropical convection. Climate Dynamics 27: 787-813.
>
> Marti, O., Braconnot, P., Bellier, J., Benshila, R., Bony, S., Brockmann,
> P., Cadule, P., Caubel, A., Denvil, S., Dufresne, J.L., Fairhead, L.,
> Filiberti, M.A., Foujols, M.A., Fichefet, T., Friedlingstein, P., Grandpeix,
> J.Y., Hourdin, F., Krinner, G., Levy, C., Madec, G., Musat, I., de
> Noblet-Ducoudre, N., Polcher, J. and Talandier, C. 2005. The new IPSL
> climate system model: IPSL-CM4. Note du Pole de Modelisation n. 26, IPSL,
> ISSN 1288-1619.
>
> Reviewed 31 January 2007
> http://www.co2science.org/scripts/CO2ScienceB2C/articles/V10/N5/C2.jsp
>

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Received on Sun Feb 4 16:51:42 2007