Hi All, 11-14-08 You may find the enclosed below interesting.
Jack Smith --------------- http://dotearth.blogs.nytimes.com/2008/11/12/will-next-ice-age-be-very-very-long/ BLOG from The New York Times, 11-12-08, By Andrew C. Revkin ``Will the Next Ice Age Be a Very Long One? A new analysis of the dramatic cycles of ice ages and warm intervals over the past million years, published in Nature, concludes that the climatic swings are the gyrations of a system poised to settle into a quasi-permanent colder state -- with expanded ice sheets at both poles. [UPDATE 11/13: Authors and critics debate the findings.] In essence, says one of the two authors, Thomas J. Crowley of the University of Edinburgh, the ice age cycles over the past million years are a super-slow-motion variant of the dramatic jostlings recorded by a seismograph in an earthquake before the ground settles into a new quiet state. He and William T. Hyde of the University of Toronto used climate models and other techniques to assess the chances that the world is witnessing the final stages of a 50-million-year transition from a planet with a persistent warm climate and scant polar ice to one with greatly expanded ice sheets at both poles. Their findings have stirred a lot of skepticism in the community of specialists examining ancient records of past climate changes and how they might relate to variations in Earth's orbit and orientation toward the Sun and other factors. I'll be adding some of their reactions overnight (I'm on the road). The Nature paper (abstract and citation below) goes on to propose that humans, as long as they have a technologically powerful society, would be likely to avert such a slide into a long big chill by adding greenhouse gases to the atmosphere. That doesn't obviate the need to curb such emissions and the prospect of dangerous climate warming in the short run, Dr. Crowley said. But it is more evidence that like it or not, the future of conditions on Earth is likely to be a function of human actions, whether chosen or not. The idea that human actions can dominate the climatic influence of things as grand as shifts in a planet's orbit is hard to grasp, but quite a few climate specialist say it's pretty clear this is the case. In 2003, I wrote an article exploring when scientists think we'll slide into the next ice age (the conventional variety). James Hansen of NASA echoed Dr. Crowley, saying that as long as we're technologically able, we'll be able to keep the big ice at bay. Strange, wonderful stuff, climate science. The paper citation details and abstract are below (it's not online except for subscribers): Nature Vol 456| 13 November 2008 doi:10.1038/nature07365 LETTERS Transient nature of late Pleistocene climate variability Thomas J. Crowley & William T. Hyde Climate in the early Pleistocene1 varied with a period of 41 kyr and was related to variations in Earth's obliquity. About 900 kyr ago, variability increased and oscillated primarily at a period of ,100 kyr, suggesting that the link was then with the eccentricity of Earth's orbit. This transition has often2 - 5 been attributed to a nonlinear response to small changes in external boundary conditions. Here we propose that increasing variablility within the past million yearsmay indicate that the climate system was approaching a second climate bifurcation point, after which it would transition again to a new stable state characterized by permanent mid-latitude Northern Hemisphere glaciation. >From this perspective the past million years can be viewed as a transient interval in the evolution of Earth's climate. We support our hypothesis using a coupled energybalance/ ice-sheet model, which furthermore predicts that the future transition would involve a large expansion of the Eurasian ice sheet. The process responsible for the abrupt change seems to be the albedo discontinuity at the snow - ice edge. The best-fit model run, which explains almost 60%of the variance in global ice volume6 during the past 400 kyr, predicts a rapid transition in the geologically near future to the proposed glacial state. Should it be attained, this state would be more `symmetric' than the present climate, with comparable areas of ice/sea-ice cover in each hemisphere, and would represent the culmination of 50 million years of evolution from bipolar nonglacial climates to bipolar glacial climates. ----------------- http://dotearth.blogs.nytimes.com/2008/11/13/more-on-whether-a-big-chill-is-nigh/ [UPDATE 11/13: Authors and critics debate the findings.] November 13, 2008 More on Whether a Big Chill Is Nigh By Andrew C. Revkin [UPDATE, 12:30 p.m.: Thomas Crowley responds to critiques below.] I was on the road yesterday and had no time to collate earth scientists' reactions to the Nature paper positing that the world, after 450,000 years of climatic turmoil (the ice ages and warm spells) is poised to enter a quasi-permanent big chill (unless we avert it, after dealing with near-term warming, with a subsequent buildup of greenhouse gases). Responses came back from James Hansen, Richard Alley and other longtime contacts in the climate science community, and I've posted them below. [UPDATE 6:00 p.m.: Carl Wunsch of M.I.T. has joined the fray, and Thomas Crowley has responded.] As I said yesterday, Dr. Hansen has long thought that the next ice age, whether short or long, will be averted -- as long as humans have the ability to alter the atmosphere -- by adjusting greenhouse-gas concentrations. And this geological time scale has little to do with the current push by many climate scientists to curb such emissions to avoid dangerous warming in the next century or two. I'll send these thoughts to the authors of the Nature paper, Thomas J. Crowley and William T. Hyde, for their reactions. Richard B. Alley, Pennsylvania State University (the 'singing climatologist'): Andy- Fascinating idea, fascinating paper. I'm a huge believer in simple models, but whenever I use one, someone is sure to point out that dramatic behaviors are often easier to obtain in simpler models. (Thermal oscillators in ice sheets, and shutdowns of the north Atlantic, are two things that seem easier in simpler models.) So a model like this is great for putting forward the hypothesis, but a range of models will be required for testing. The glaciological community has for decades harbored the widespread belief that the thermal evolution of the ice sheet, and the effect of this evolution on ice flow, are central in the ice-age cycling (not all communities agree, but there is plenty of literature on this from the land-ice crowd), so use of a temperature-independent rheology for the ice leaves out one favored explanation for termination of extensive glaciation. With CO2 feedbacks and north Atlantic feedbacks not in the picture, I believe that the current paper leaves out Mo Raymo's (1997) idea that termination of a glaciation requires storage of excess ice in the northern hemisphere -- sort of a "the bigger they are, the harder they fall" idea, which can be found in earlier and later literature as well. (Much of the glaciological literature on termination of large ice ages requires ice-sheet growth past a threshold size.) In a short piece in the PAGES Newsletter, George Denton, Wally Broecker and I linked this excess ice and orbital forcing through ocean circulation to control of CO2, and others are surely thinking along the same lines. So, if some of these ideas on termination of glaciations are correct (ice-sheet temperature, ocean circulation and CO2), and all of these are omitted from the current model, it leaves open the possibility that a more comprehensive model would get a different result. Richard Julie Brigham-Grette, University of Massachusetts, Amherst (whom I've consulted on Arctic climate shifts many times): I agree with Richard. There are so many exceptions ("we do not consider glacial-interglacial changes in CO2 or North Atlantic heat sources"; other experiments listed have "no ocean dynamics." The paper represents a series of sensitivity tests, theoretical as you say, but it might at least stir more work in understanding abrupt change and system dynamics. There are many things we don't understand -- like why the EPICA interglacials before stage 11 have a lower threshold level than after. Sometimes even simple models help us think in new ways, and that is what science does. James E. Hansen, NASA Goddard Institute for Space Studies: Look at Figure 3 in our 'Target' paper Target CO2: Where should humanity aim? [pdf]. Yes, the Earth has been on a 50-million-year cooling trend with superposed glacial-interglacial oscillations.* It would take only a small further reduction in climate forcing (less long-lived GHGs or whatever) to yield more ice during the glacial phase of glacial-interglacial oscillations. But that is entirely academic at this point, unless humans go extinct. Although orbital variations instigate the glacial-interglacial swings, the mechanisms for climate change are changes in GHG amount and surface albedo (as we show in Fig. 1 of our paper) -- those mechanisms are now under the control of humans. Another ice age cannot occur unless humans go extinct. It would take only one CFC factory to avert any natural cooling tendency. Our problem is the opposite: we cannot seem to find a way to keep our GHG forcing at a level that assures a climate resembling that of the past 10,000 years. Jim *The long-term cooling is related to the situation with the continents -- not much subduction of carbonate-rich ocean crust now. The site of strong subduction associated with India plowing through the Tethys Ocean ended when India crashed into Asia 50 million years ago, so that source of CO2 diminished. Daniel P. Schrag, Harvard University (here's his formula for action on global warming): I am very, very skeptical. This is all fun and games with a climate model. (and theirs is not a particularly good one). I do not believe that their results have much to do with how the real earth would or will behave. And I think many climate scientists would agree with me. Why don't you ask Carl Wunsch or Kerry Emanuel what they think? [I've sent a query to Dr. Wunsch.] Dan More on the paper and how it's stirred debate is online at Discover magazine. Again, the time scale here is far beyond what's relevant to climate policy now (meaning the next 100 years or so). As I've written before, Homo sapiens appears to be in the uncomfortable position of being the first life form to exert a global-scale influence (for better or worse) and be aware of that reality (plants altered the atmosphere, too, but most likely didn't realize it). Do you think we've absorbed this yet? [UPDATE:] Thomas Crowley has responded to this round of critiques: Andy, Not surprised by the replies, but don't buy them: As we said in the paper there is a huge gulf between the original simple energy balance model from Budyko and the one we use. Yet the basic results are almost exactly the same. The fact that our model does a surprisingly good job with simulating the last 400,000 years of global ice volume, with no change in model physics and only one linear change in boundary conditions, argues for the fact that, despite plausible deficiencies, we have done a surprisingly good job of simulating the pattern of fluctuations in ice volume. Another example can be drawn from the energy balance model calculations for the snow/ice instability - despite all the details not in the original energy balance model, much more complex general circulation models have now been shown to have the same behavior - a citation from 1994 (!) which we have in our document but is almost universally ignored by the geological community but has been supported by subsequent work with another model (Bette Otto-Bliesner). The criticisms also ignore the analysis of data which almost undeniably indicate increasing variability towards the present - is one supposed to think that this variability will now just stay anchored at the present level? That to mean seems more implausible. I am quite comfortable with our conclusions and remain unconvinced by the first wave of counter-arguments. Tom [UPDATE 2:30 p.m.:] Carl Wunsch of the Massachusetts Institute of Technology has fired quite a broadside: "Surely this isn't science in any conventional sense. Taking a toy model and using it to make a 'prediction' about something nearly a million years in the future, is a form of science fiction -- maybe interesting in the same way a novel is, but it isn't science. The prediction itself is untestable -- except a million years from now, and the model 'tests' that quoted are carefully chosen to be those things that the model has been tuned to get 'right,' with no mention of the huge number of things it gets wrong. How many times do 'if', and 'may' get used in the paper? If I make a four-box model of the world economy, and predict the US stock market level 500 years from now, who would pay any attention? Climate is far more complicated than the world economy, yet supposedly reputable journals are publishing papers that superficially look like science, but which are the sort of thing scientists will speculate about late at night over a few beers. It doesn't deserve the light of day except as the somewhat interesting mathematical behavior of a grossly over-simplified set of differential equations. Why should anyone take it seriously? The wider credibility of the science is ultimately undermined by such exercises." Dr. Crowley has responded to Dr. Wunsch (I'll end the up-front debate here and any further comments by scientists can come in the comment string below): These are pretty harsh words and they almost sound convincing. Except that we do make an attempt to validate the model with respect to how it has performed against the best estimate of global ice volume we have - Shackleton's 2000 record (I might add that I am not sure of any other modeling study that has tried to validate itself against the Shackleton record). And it is this very same model run that is run past the present. We also point out that similar processes appear to have gone on in the deeper geological past with respect to Antarctica. We again point out that observations clearly indicate an increase in variability towards the present. Does one somehow expect that just to stop? If so, why, Carl? With respect to the dismissal of the model, we point out that we have separately applied the model to the great Permo-Carboniferous glaciation on Pangaea and to the Snowball Earth problem (although some people do not like one of the solutions it produces). Are not these tests of the models, or a separate test we have done with respect to noise forcing of the model (referred to in paper)? This is actually a fairly well tested model (Dick Peltier has done separate work on the Pleistocene - again referred to in our paper). Sorry Carl, this is science; you might not like it, but it is science.''
