Sea level is scarcely rising: The average rise in sea level over the past 10,000 years was 4 feet/century. During the 20th century it was 8 inches. In the past four years, sea level has scarcely risen at all. As recently as 2001, the IPCC had predicted that sea level might rise as much as 3 ft in the 21st century. However, this maximum was cut by more than one-third to less than 2 feet in the IPCC's 2007 report. Moerner (2004) says sea level will rise about 8 inches in the 21st century. Mr. Justice Burton, in the UK High Court, bluntly commented on Al Gore's predicted 20ft sea-level rise as follows: "The Armageddon scenario that he depicts is not based on any scientific view." A fortiori, James Hansen's prediction of a 246ft sea-level rise is mere rodomontade. Sea-level rise since the beginning of 2006 has been negligible. Source: University of Colorado, 2009, release 4.
Firstly, the characterization of past sea level rise is simply and wildly false.
(courtesy of Global Warming Art)
Secondly, the IPCC AR4(2007) sea level assessment explicitly disincluded any possible rise from ice sheet melt because of increased uncertainty from the time the IPCC TAR(2001) report came out. This uncertainty arose from the fact that Greenland and West antarctica are responding much faster and in ways we do not understand to climate change. The AR4 figures are only about thermal expansion and glacial melt water. Real Climate talked about this here.
Thirdly, who care what Justice Burton says, or even Al Gore? On the other hand, James Hansen knows what he is talking about even if crakar does not. The only place a figure of 246 ft sea level rise can come from is a calculation of how high waters would rise if all ice on the planet melted, (or at least GISS and WAIS, I'm offline now so maybe someone in the comments can post the right citations). No one at all knowledgable in climate science thinks that that can happen in anything less than centuries (including Al Gore who never said anything different). Hansen has never claimed otherwise. Post a quote and a link or drop that turd right now!
Fourthly, we are concerned with climate, with 30+ year trends. Fluctuations over a few years or even a decade are noise not signal.
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For 246 feet (over 70 meters), you're looking at melting the entire Greenland Ice Sheet, the entire West Antarctic Ice Sheet, and the entire East Antarctic Ice Sheet, and waiting for isostatic adjustment to bring parts of Greenland and Antarctica that are currently pressed below sea level by the weight of the ice sheets back to their adjusted, above sea level, elevations. For melting East Antarctica or for isostatic adjustment, the time scale is thousands of years, not mere hundreds.
Hansen, it should be needless to say, but probably is not, has never predicted 246 feet sea level rise on any short time scale. (Short, in this case, meaning anything less than thousands of years.) On the other hand, it's not past the realm of reasonable in the science to think it possible that if we continue on a business as usual path, we will set climate on a course for such a 70+ meter sea level rise. It would take the thousands of years, still, but that would be the expected outcome at some level of human activity on the climate system.
For an old rendition of who the players are in sea level rise, with some magnitudes and time scales, I'll recommend my old Catastrophic sea level rise FAQ. Old meaning 1997. One thing the age is useful for is to see just how much our thoughts on Greenland have changed. Back then, there was no expectation that Greenland could be a major player on rapid sea level rise. West Antarctica was the only serious player for that. Today, if anything it seems that Greenland is the bigger candidate.
That relates to a different bit that crakar has wrong. The 4th IPCC report had unreasonably low estimates for sea level rise. This is because the work that showed Greenland could collapse much faster than we'd previously thought didn't come out until after the deadline for inclusion. (But was well before the release of the report.) Consequently there were, shortly following the release, much better estimates of sea level change. iirc, the top end of the 4th report -- neglecting this new knowledge was 0.59 meters. After starting to make reasonable allowance for the now-known processes, high end figures are is 2-4 times greater. 1-2 meters (3-7 feet).
Posted by: Robert Grumbine | October 24, 2009 9:41 PM