Wednesday, May 6, 2009

I have stolen this post from Mark B over at climateprogress. This should get some attention when it is completed and released:

6 meter sea level rise possible by 2100?

A new comprehensive scientific study:

Note that this report is still pending review, but chapter 5 states:

“Rates of sea level rise at least twenty times the current 3.1 mm/yr sustained over more than a century have been measured for the transition to the current warm period following the termination of the last ice age and during some of the warmer intervals of the last ice age. Until improved predictive capability is achieved, this can be regarded as a reasonable upper bound of Antarctica’s potential contribution to global sea level. This maximum rate (62 mm/yr) would lead to a 6-meter sea level rise by 2100, but such rates occurred when there was considerably more ice on the planet. Even a significant fraction of such a contribution would come at great human and environmental cost, underscoring the need for a better understanding of ice-sheet sensitivity to climate change. ”

The qualification “such rates occurred when there was considerably more ice on the planet” is important, but so is the rate of temperature change projected for this century and recent temperature change.

Other findings:

“Concern that the sea-level projections may be biased low has been reinforced by a comparison showing that observed sea level has been rising more rapidly than the central range of the IPCC projections, since 1990, and is at the very upper end of the IPCC projections (Rahmstorf et al, 2007) suggesting that one or more of the model contributions to sea-level rise is underestimated .”

“For the modern satellite period (since 1993), sea level has been rising more rapidly at an average rate of about 3.2 ±0.4 mm/yr. Note that these rates of increase are an order of magnitude faster than the average rate of rise over the previous several thousand years, but significantly slower than the rates of rise at the end of the Last Glacial Maximum and at the end of the Younger Dryas event (see chapter 3).”

I find this interesting. The rate of sea level rise at the end of the last glacial maximum was high because global mean temperatures were rising. We’ve begun a warmup due to human activities and the rate is accelerating again.

“However, sea-level projections closer to and beyond 2100 are critically dependent on future greenhouse gas emissions, with both ocean thermal expansion and the ice sheets potentially contributing metres over centuries for higher greenhouse gas emissions.”

Obviously, we have some control over how much sea levels rise.

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