Hi John‹First, I would note that polar amplification is included in the estimates of the rates of warming (whether 0.2 C/decade or higher to get 4 C). Cooling the Arctic would reduce this effect.
Second, on the cause of faster sea ice reduction than models are projecting, I know there are a lot of suggestions this is due to soot emissions. My problem with that explanation is that the observations described in Quinn et al ( Quinn P K, Shaw G, Andrews E, Dutton E G, Ruohoairola T and Gong S L ,2007: Arctic haze: current trends and knowledge gaps, Tellus B 59 99114) indicates that soot deposition in the Arctic has been declining. It is true that global emissions may be going up (due to China and India, one would presume), so a pure correlation suggests it might well be soot that is correlated with the increased decline of sea ice, but studies of Arctic haze (presented at last December¹s AGU meeting in SF) indicate that the air trajectories into the Arctic come mainly from Europe (Atlantic to Urals, so including much of Russia), and black carbon emissions from Europe have come down due to emissions controls and from Russia and eastern Europe due to shutdown of the worst power plants due to economic slowdown. Reduced black carbon into the Arctic would be leading to less uptake of solar, so hard to see how increasing global black carbon emissions are accelerating the sea ice retreat (what matters are trajectories into the Arctic and what is happening in the upwind regions). The observations also show that sulfate deposition has been going down, for the same reason, and this would likely increase the solar radiation reaching the sea ice (clear skies would be cleaner and clouds less bright), so, as noted in my ERL article, my supposition is that it is reduced sulfate that is leading to the acceleration of sea ice melting. This all needs to get confirmed by checking out the data on light levels reaching the surface through the year, which Dutton and NOAA may well have. If this sulfate hypothesis is correct, then we have thus performed something like a reverse geoengineering experiment. And we can estimate roughly what the flux change was. And so, as the article suggests, we might well be able to reverse the warming by increasing tropospheric sulfate (which I favor instead of stratospheric sulfate‹see article for reasoning) during the sunlit season in the Arctic, and so for a lot less SO2 emissions than we have had in the past (so we can see what ecological and other effects were). As I say, a good bit of supposition, but a lot that could quite readily be investigated over several years. On issue of uncertainties and surprises, I think it is quite possible that trying to push back toward conditions of recent past via tropospheric sulfate might well, after a relatively short and focused research and development effort, be better understood and have less likelihood of surprises than proceeding along with greater and greater GHG concentrations and warming. Cooling the Arctic would have the advantage of giving back the amplification effect‹so help keep midlatitudes from warming so much and might well slow the rate of rise of sea level, even perhaps helping to stabilize the polar ice sheets. There are indeed questions to be looked at (e.g., would SO2 become sulfate in the Arctic, would geoengineering in the Arctic shift the ITCZ and could that be balanced by some sulfate injection over the Southern Ocean, etc.), and these topics seem to me to be well within our research capacity because the sulfate loading likely needed is, at least in the Arctic, within our experience. I am all for reducing black carbon emissions further to help the sulfate effort along and Tim Lenton may be right that ridding the Arctic of all soot deposition would allow sea ice to return‹another question that could readily be looked at. But I think the changing and geoengineering role of sulfate may well be more critical. I also agree that time is critical. The Arctic is already in what might be called dangerous decline. I don¹t think waiting to use geoengineering at some distant future point is the way to go for then any application would have to be very strong to induce the desired result, if it is possible at all. One normally tries to put out fires when they are small or localized than when the whole building is aflame. Best, Mike MacCracken On 11/1/09 5:26 PM, "John Nissen" <[email protected]> wrote: > > Hi Mike, and others, > > What would happen if we could halt all CO2 emissions overnight? > > As you say, Mike, we have to add up all the climate forcings. If CO2 > emissions were halted overnight by closing coal-fired power stations, then > we'd have: > 1) much of the CO2 positive forcing (currently around 1.6 W/m-2) continuing > for centuries; > 2) the almost immediate removal of sulphate from troposphere and thus loss of > its cooling effect (resulting in increased net positive forcing); > 3}the removal of black carbon, aka soot, and (a) its slight reflective effect, > but also (b) its darkening effect on snow and ice in the Arctic. > > As you say in your paper, as emissions continue to increase, both warming and > the commitment to future warming are increasing at the a rate of 0.2 degrees > per decade. This equates to 2 degrees this century, from effect (1). > Moreover, it appears, from the Climate Congress in Copenhagen last March and > subsequently, that the current trajectory of emissions could lead to at least > 4 degrees warming [1]. > > But I believe, whatever we do about emissions, the so-called "polar > amplification" effect will continue. This is on the assumption that the > regional warming in the Arctic is largely driven by warming surface waters of > the Gulf Stream entering the Arctic ocean. As the Atlantic surface waters > would continue to warm, the amplification would continue. Thus the Arctic sea > ice would continue its trend towards summer disappearance. (However Tim > Lenton disagrees, saying that the removal of carbon black alone would be > enough to halt the retreat, see 3b above.) > > Our conclusion must be that emissions reductions, however severe, are (by > themselves) extremely unlikely to prevent a temperature increase of at least 2 > degrees this century, and certainly cannot prevent the Arctic sea ice summer > disappearance (if the current trend for retreat continues). Removal of carbon > black will undoubtedly help to preserve Arctic sea ice, but by itself could > not be relied upon. > > Thus the science is conclusively pointing to the need to be prepared for SRM > geoengineering to cool the Arctic. > > It is often said the SRM geoengineering should be used "as a last resort". > But that assumes that we wait until things get much worse, when it could be > too late. So when is the best time for deployment? Surely it is before the > positive feedback effects grow any larger. Therefore: > > The optimum time for SRM deployment is right now. > > And if you consider the risks of geoengineering are enormous, spend your > energy on finding a way to reduce them! We can be researching on this while > in parallel gearing up for large scale deployment. > > One of the greatest dangers from letting the Arctic sea ice disappear, and > Greenland ice sheet disintegrate, is the effect of sea level rise on food > supply. Lester R. Brown, founder and president of the Earth Policy Institute, > wrote about the possibility of food shortages bring down civilisation [2]. He > is acutely aware of tipping points and danger of sea level rise. He said > about our current predicament: > > Time is our scarcest resource... The world is in a race between political > tipping points and natural ones... Can we prevent the Greenland ice sheet > from slipping into the sea and inundating our coastlines? ... It is hard to > overstate the urgency of our predicament. Every day counts. > > I recommend reading the whole article. It helped me to appreciate what we are > up against. > > Cheers from Chiswick, > > John > > [1] Four degrees and beyond: How soon is it coming? > http://blogs.nature.com/climatefeedback/2009/09/4_degrees_and_beyond_how_soon. > html > > [2] Scientific American, May 2009. "Could food shortages bring down > civilization?" by Lester R. Brown: > http://www.scientificamerican.com/article.cfm?id=civilization-food-shortages&p > age=5 > > --- > > Mike MacCracken wrote: >> >> If we stopped all emissions, of all GHGs and aerosols, what would be removed >> first are the aerosols. The sulfate cooling offset is estimated at 1.1 W/m2 >> so their loss would lead to a strong warming influence. The black carbon is >> estimated by IPCC at about 0.4-0.5 and by Ramanathan and others to be twice >> that. Their loss would lead to a less positive forcing, so, if all these >> emissions stopped, the net would be a small warming influence. Stopping all >> emissions, of course, tropospheric ozone warming influence would also end >> over months. And then methane influence would go down over decades. So, one >> would tend toward a lessened warming influence. And some, but not a lot of >> the CO2 would be taken up. So, stopping all forcing does reduce the warming >> influence. >> >> If you want to see a graph of the effects of ending all GHG emissions (the >> tables have information on aerosols), go to a recent proceedings paper I >> have posted at http://www.climate.org/PDF/MacCracken_Erice.pdf, where you >> will also see my views about how to utilize the different time scales to >> promote an agreement between developed and developing nations at >> http://www.climate.org/topics/climate-change/maccracken-proposal-north-south >> -framework.html >> >> These notes are all about forcings, as the forcing will determine the >> climate that the world heads toward. The ocean slows the transition to >> equilibrium. If you want to see what is, in effect, a geoengineering set of >> simulations by the modeling groups of the world, look at the graph of the >> IPCC projections of temperature. One sees the results for the various SRES >> scenarios, but the yellow/orange line shows the results for holding all >> concentrations and aerosol loadings constant. Holding CO2, N2O, and >> halocarbon concentrations constant requires some very large percentage >> reduction in their emissions; for methane the cutback is much less. But >> cutting CO2 emissions by 80-90% to keep its concentration constant will >> surely lead to a sharp reduction in SO2 emissions, and so a very sharp >> reduction in their cooling influence, and perhaps in black carbon and its >> somewhat smaller warming influence, meaning that to hold the aerosol burden >> constant, there must be substantial emissions of aerosols/aerosol precursors >> (just what is being discussed for geoengineering, except in the >> troposphere). You can see that about 0.5 C further warming goes on, and this >> is the oceans catching up to the land. >> >> Mike MacCracken >> >> >> On 11/1/09 12:34 PM, "John Gorman" <[email protected]> >> <mailto:[email protected]> wrote: >> >> >> >>> >>> I think the point is as follows: >>> >>> If we fix the CO2 at say 2 times preindustrial then the net forcing will not >>> instantly get the global temperatures up to their long term steady state. >>> The oceans will lag. >>> >>> It sounds as if you are thinking of the net forcing which has resulted in >>> the temperature rise for the land has gone away-but it hasn't in the case >>> you have quoted. The CO2 level will stay constant for centuries even if all >>> emissions stop today. >>> >>> There was a very recent post or link on this recently which quoted 3deg for >>> doubling of CO2 in the short term but 6deg long term. This link, which I >>> cant find just now, used data from some much earlier time when the doubling >>> had already resulted in almost completely ice free poles. This is presumably >>> what will happen now if we get to doubling and don't do something about it. >>> The Arctic is melting now. It isn't going to stop melting just because we >>> stop increasing the temperature. So there is a temperature inertia or lag >>> due to ocean heat capacity but an even bigger one due to ice cap latent heat >>> of melting. >>> >>> john gorman >>> >>> >>> ----- Original Message ----- >>> From: "John Nissen" <[email protected]> <mailto:[email protected]> >>> To: <[email protected]> <mailto:[email protected]> >>> Cc: "geoengineering" <[email protected]> >>> <mailto:[email protected]> >>> Sent: Sunday, November 01, 2009 1:56 PM >>> Subject: [geo] Re: Jamais Cascio-- on the problematic idea of 350 >>> >>> >>> >>> >>>> >>>> >>>> Hi all, >>>> >>>> Jamais Cascio is described as an "environmental futurist" and has >>>> written a book with the title "Hacking the Earth" [1]. It's great that >>>> somebody is pointing out the implication of the 350 ppm target! >>>> >>>> But he shares a very common scientific belief which I do not understand: >>>> >>>> "(Even more troubling: even if we stopped all anthropogenic carbon >>>> sources immediately, we'd still see continued warming for at least >>>> decades, possibly longer, simply from the thermal inertia of the >>>> oceans. Absent a radical step, we're guaranteed to see at least >>>> another degree or two of warming, no matter what we do.)" >>>> >>>> >>>> With global warming, the land and atmosphere warm faster than the >>>> oceans. If emissions stopped overnight, the oceans would still be >>>> warming up, thus cooling the atmosphere, rather than warming it. Thus >>>> the thermal inertia of the oceans would drag down the global temperature >>>> (mean of surface temperatures over the globe). Am I right? >>>> >>>> Cheers, >>>> >>>> John >>>> >>>> [1] http://www.lulu.com/content/6048806 >>>> >>>> -- >>>> >>>> Dan Whaley wrote: >>>> >>>> >>>>> >>>>> You will appreciate this one Greg... >>>>> >>>>> http://www.fastcompany.com/blog/jamais-cascio/open-future/350 >>>>> >>>>> 350 >>>>> BY Jamais CascioTue Oct 27, 2009 at 2:55 PM >>>>> 350 parts-per-million is the carbon limit. How will we get back there? >>>>> >>>>> 350.org >>>>> >>>>> It may be odd to focus a political movement on a relatively obscure >>>>> bit of science, but a world-wide push to limit concentration of >>>>> atmospheric carbon dioxide to 350 parts-per-million made a big splash >>>>> last week, with rallies and gatherings all over the planet focusing on >>>>> drilling this number into the public consciousness. The number comes >>>>> from work done by (among others) NASA's James Hansen, looking for >>>>> potential climate "tipping points." 350ppm for CO2 is a safe limit-- >>>>> get too much beyond it, and the dangers multiply. >>>>> >>>>> It's an audacious goal, for reasons of both communication and science. >>>>> >>>>> In terms of communication, while a simple meme like "350" or "350ppm" >>>>> fits nicely on protest signs and bumper stickers, it's a term without >>>>> much context for the vast majority of the populace. In and of itself, >>>>> that's not a problem; however, it can make a visceral connection to >>>>> the concept more difficult. Activists adopting the 350 meme will need >>>>> to match rhetoric with education, to make the number meaningful. >>>>> Again, not impossible, but likely an ongoing challenge. >>>>> >>>>> The scientific audacity with the 350 meme comes from a single, simple >>>>> fact: current concentration of atmospheric CO2 is roughly 385ppm. That >>>>> is, we already exceed the 350 limit, and most climate scientists say >>>>> we'll be hard-pressed to keep from going over 450ppm by the middle of >>>>> the century. And carbon dioxide takes centuries to cycle out of the >>>>> atmosphere--even if we stopped all anthropogenic sources of CO2 right >>>>> this minute, we'd still see too-high concentrations for years to come. >>>>> >>>>> (Even more troubling: even if we stopped all anthropogenic carbon >>>>> sources immediately, we'd still see continued warming for at least >>>>> decades, possibly longer, simply from the thermal inertia of the >>>>> oceans. Absent a radical step, we're guaranteed to see at least >>>>> another degree or two of warming, no matter what we do.) >>>>> >>>>> If this sounds like I think the 350 movement is a bad idea... I don't. >>>>> I rather like the simplicity of the meme, and the target is--if >>>>> difficult--smart. It's not saying "let's keep things from getting too >>>>> much worse," it's saying "let's make things better." That's the kind >>>>> of goal I like. >>>>> >>>>> But getting back to 350ppm requires more than a rapid cessation of >>>>> anthropogenic sources of atmospheric carbon. It requires an >>>>> acceleration of the processes that cycle atmospheric CO2. Planting >>>>> trees is an obvious step, but it's slow and actually doesn't do enough >>>>> alone. We'll also need to bring in more advanced carbon sequestration >>>>> techniques, such as bio-char. The combination of the two would likely >>>>> bring down atmospheric carbon levels, given enough time. >>>>> >>>>> Unfortunately, we may not have enough time. >>>>> >>>>> If efforts to eliminate carbon emissions continue to happen at a pace >>>>> most generously described as "leisurely," we will almost certainly >>>>> face a situation where we approach and even pass critical tipping >>>>> point concentrations. Ocean thermal inertia means that climate >>>>> benefits from emission cessation won't be seen for decades. There's a >>>>> very real scenario where finally get it right, both cutting out >>>>> anthropogenic emissions and sequestering megatons of carbon via plants >>>>> and bio-char ... and still face terrible environmental consequences, >>>>> simply because we didn't act fast enough. >>>>> >>>>> That's where we start to talk about much more radical, and potentially >>>>> dangerous, steps. Geoengineering to hold temperatures down is one; to >>>>> meet the 350ppm goal, we will likely also start looking at large-scale >>>>> methods to sequester carbon, such as with triggered algae blooms. >>>>> >>>>> 350ppm is an audacious goal, but one worth striving for. But its >>>>> challenge comes not just in the effort to eliminate anthropogenic >>>>> carbon emissions around the world--a massive endeavor alone--but also >>>>> in figuring out how to remove the extra carbon already there. I hope >>>>> that the 350 leaders have thought through the implications of what >>>>> that means. >>>>> >>>>> [Images: "Organized Spelling B" by Wade in Da Water on Flickr, >>>>> Creative Commons Licensed; "Summer Bloom in the Baltic Sea" by NASA >>>>> Visible Earth] >>>>> >>>>> >>>> >>> >>> >>> >>> >> >> >> >> >> >> >> > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
