Saturday, January 12, 2008

Past and Future Melts

On the Science Briefs page of the NASA GISS website about a year ago, Dr. Vivien Gornitz posted Sea Level Rise, After the Ice Melted and Today, a succinct article on the sea rises that occurred as the last ice age was ending, from 23 to 3 kiloyears ago. A chart shows meltwater pulses mwp-1Ao, mwp-1A, mwp-1B and mwp-1C, and the text explains research into the sources and sea rise rates of each pulse. None had an average rise rate much greater than 3 meters per century, but occasional centuries did experience rises faster than the average for whatever pulse was then underway.

Transitions from glacial to interglacial periods had more ice vulnerable to rapid melting than our planet has today. Therefore that average meltwater pulse rate of 3m per century, with some lags and surges, is probably the most severe we can plausibly expect for the real near future and succeeding centuries = even if the climate change causing the melt is faster than the end of the last glacial was.

In choosing an average rise rate for our Meltwater fictional geochronology, paleoclimate evidence would suggest the 3m figure as a realistic upper bracket, just as 1.6m is a likely lower bracket.

A later “molten” civilization at high latitudes, ideally after all the perennial polar ice has melted, is our vantage point for any retrospective discourse. However, the further into the future we set this viewpoint civilization, the harder that civilization will be for us to describe and our readers to understand. A realistic upper-bracket sea rise rate means that some 3 kiloyears would need to elapse before the polar ice is gone. A rate between the brackets would require an even longer interval. So I suppose we need to ask: Should our dramatic need for a less remote and more intelligible viewpoint civ trump realism, leading us to posit an average rise rate greater than 3m per century? My tentative answer: No. The sci-fi challenge of narrative realism, so often shirked, is well worth facing. What do you think?