> I think it's just that people are trying to decide whether Hansen is > actually saying that the IPCC authors were wrong to write what > they did at that time, or merely that subsequent evidence has > overturned their conclusion. In fact, it doesn't seem clear to me > that either version is all that reasonable.
I think I had discovered why you and William have difficulty seeing things from our POV. You both have strong mathematical backgrounds and so you use deductive reasoning when approaching scientific issues. When something has been proved true with deductive reasoning, it is always true. Once someone has worked out that 123 plus 765 equals 888 that is true for ever. That fact never changes. But with earth science, just because someone PROVES that the Greenland ice is melting at 104 +/- 54 km^3 yr^-1 during the two years from 4 - 2002 until 4-2004 does not mean that the rate is still true today. In fact, during the two years 5 - 2004 until 4 - 2006 the rate was 342 +/- 66 km^3 yr^-1. In other words, the mass loss more than trebled! See: "Our results show a significant increase in the rate of Greenland mass loss, starting in spring 2004. A fit to the GRACE results for all Greenland before and after April 2004 yielded ice loss trends of 104 +/- 54 lm^3 yr^-1 during April 2002 - April 2004, and 342 +/- 66 km^3 yr^-1 during May 2004 - April 2006." Velicogna & Wahr Nature 2006. Of course, you may reply that with your analysis of climate sensitivity you are using Bayesian logic which is a form of inductive reasoning. But science is not based on inductive reasoning. "...scientific reasoning is always defeasible ..." See: http://william-king.www.drexel.edu/top/prin/txt/Intro/Eco112c.html It is not just Hansen who is criticising the IPCC TAR. Velicogna & Wahr [2006] begin their abstract "In 2001 the Intergovernmental Panel on Climate Change projected the contribution to sea level rise from the Greenland ice sheet to be between -0.02 and +0.09 m from 1990 to 2100 (ref. 1). However, recent work (refs. 2-4) has suggested that the ice sheet responds more quickly to climate perturbations than previously thought, ..." and Chen et al. [Science 2006] write "GRACE clearly detects a rate change in the recent period, suggesting a contribution of about 0.54 mm/year to global sea level rise, well above earlier assessments (23)." [23 = IPCC TAR pp 639 - 694.] > Many of Hansen's references are to his own presentation (ref 17) which > could IMO be arguably described as handwaving, rather than any clear > scientifically-justified quantitative argument. I think if septics were > to make opposing arguments on a similar basis they would risk getting > vigorously fisked on certain climate blogs I could mention :-) One should be careful when using a pejorative term like "handwaving." You could be accused of using ad hominem arguments. Moreover, it is not handwaving to use defeasible facts to argue that the melt of the Greenland ice is accelerating. A handwaving argument would be that it is all due to natural cycles, for which there is no evidence. > However, I have to admit I've got a bit of a soft spot for the man. OYOH, I have always been suspicious of a member of the establishment. Their views tend to be conservative (without a capital C) and I feel that Hansen's are too. He says we have ten years to turn things round, but it is clear to me we have already passed the tipping point as far as the Greenland ice is concerned. In his 25. Summary : Ice sheets, he writes: "C. Once ice sheet disintegration begins, there is the possibility of a system out of our control. We cannot tie a rope around a collapsing ice sheet." The disintegration has begun, and there is no lasso. Our only hope is that the US Cavalry will ride to our rescue, and erect a sunshade, or cover the Sahara in tin foil. They could even explode a nuclear bomb in the middle of an ocean to inject water into the stratosphere. That worked in 1946 and 1963. Otherwise "Waur doomed :-(" [Private Frazer] Cheers, Alastair. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/globalchange -~----------~----~----~----~------~----~------~--~---
