Dear Ken, I've already looked at this interesting paper [1], from Jim Hansen and Mikiko Sato - but I'd not read before of his conjecture about rate of ice mass loss doubling per decade, producing many metres of sea level rise this century. But the implication is that the situation can be saved simply by reducing fossil fuel emissions! Is that the prescription that you are complaining about? Wouldn't a well-considered prescription be welcome from somebody as eminent as Prof Hansen? Geoengineering for example! I don't see a way out of our predicament without it. Do you, Ken?
Does Hansen accept that 90% sea ice could be gone as soon as at end summer 2016? (BTW, I've another reference to this date we've been arguing about [2].) Hansen seems to dismiss methane as always producing less forcing than CO2: "*This sensitivity has the merit that CO2 is the principal GHG forcing and perhaps the only one with good prospects for quantification of its long-term changes.*" (page 15) However the paper is relevant to the methane issue in several ways. One argument, which I've heard from Jeff Ridley, is that there is no sign of a methane excursion at previous interglacials* such as end-Eemian, when it was hotter, so we don't need to worry about having an excursion now. Hansen shows that it was never hotter than it is now (in Holocene) by more than one degree. Elsewhere Hansen points out that the current rate of global warming is much higher than it has been for millions of years. Andrew Lockley suggests it's higher than even it was at the PETM some 55.8 million years ago, when temperatures rose about 6 C [3]. That rate of change is important, because of methane's short lifetime. The increasing speed of change implied by Hansen's climate sensitivity is thus relevant to methane. A further way that the paper is relevant to methane is because of climate sensitivity to radiative forcing. The paper suggests various alternative values that could be taken - see [1] table 1. If we get over 2 W/m-2 from methane, then that certainly takes us over the danger line of 2 degrees global warming, using his argument. Cheers, John * During the past 800,000 years, methane never rose much above 700 ppb until recently, see [1] figure 2 [1] Full paper http://arxiv.org/ftp/arxiv/papers/1105/1105.0968.pdf Abstract here: http://arxiv.org/abs/1105.0968v3 [2] http://www.bbc.co.uk/news/science-environment-13002706 [3] http://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_Thermal_Maximum --- On Thu, Jul 21, 2011 at 11:07 PM, Emily <em...@lewis-brown.net> wrote: > Hi, > > here is a recent paper from Jim Hansen,including some figures I've read > before, which stunned me: > > "In the early Pliocene global temperature was no more than 1-2°C warmer > than today, yet sea level was 15-25 meters (50-80 feet) higher." > > best wishes, > > Emily. > > > *Paleoclimate Implications: Accepted Paper and 'Popular Science'* > > > "Paleoclimate Implications for Human-Made Climate Change" has been > reviewed, revised in response to the referee's suggestions, and accepted > for publication in "Climate Change at the Eve of the Second Decade of > the Century: Inferences from Paleoclimate and Regional Aspects: > Proceedings of Milutin Milankovitch 130th Anniversary Symposium" (Eds. > A. Berger, F. Mesinger and D Šijački), Springer. > > This final version has also been published in arXiv:1105.0968v3 > [physics.ao-ph] > < > http://columbia.us1.list-manage.com/track/click?u=0ebaeb14fdbf5dc65289113c1&id=fbefcc8464&e=60a7483168 > > > > A__'popular science' summary > < > http://columbia.us1.list-manage.com/track/click?u=0ebaeb14fdbf5dc65289113c1&id=d3b93e0894&e=60a7483168 > > > of the paper, intended for lay audience, is available. > > Thanks especially to reviewer Dana Royer for helpful comments, > foundations and NASA program managers for research support, and a number > of people for comments on an early draft of the paper, as delineated in > the acknowledgements. > > Jim Hansen > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to geoengineering@googlegroups.com. > To unsubscribe from this group, send email to > geoengineering+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
