In a recent post about sea level rise, we highlighted a paper by the University of Colorado’s Tad Pfeffer and others in which they show that one can rule out more than 2 meters of sea level rise in the next century. While we liked the paper very much, we also complained that Pfeffer and colleagues had created a bit of a straw man, by implying that it had been seriously proposed that Greenland’s near term contribution to sea level rise could be much larger than that. In fact (we said), none of us in the climate science community ever took such ideas seriously, even if the popular press thought we did. Tad responds by pointing out that in fact there is published work attributing considerable likelihood to such extreme scenarios, and that there are numerous studies that at the very least strong imply it. He also reminded me that their paper actually rules out a contribution of more than about 50 cm from Greenland, significantly below some other recent published estimates. That makes their work even more important, since there are several publications that definitely consider upwards of one meter (from Greenland alone) by 2100 to be plausible. Pfeffer et al. conclude that that is simply not the case (at least in their informed view). Still, we remind readers that our chief complaint was that Pfeffer et al.’s work was taken by many in the media as a downward revision to sea level rise estimates, whereas in fact most informed estimates had put an upper limit well below that. See our earlier post on the IPCC Sea Level numbers.
In any case. Pfeffer et al’.s response to our post follows below. Fair enough.
A response to RealClimate’s post on our paper about sea level rise
W.T. Pfeffer, J.T. Harper, and S. O’Neel
15 September 2008
We have read with interest – and, we admit, surprise – the RealClimate post concerning our 5 September publication in Science entitled “Kinematic Constraints on 21st Century Sea Level Rise.” The source of our surprise, however, is probably not what the RealClimate authors imagine – we had fully expected a vigorous defense of very high rates of sea level rise (greater than 2 m/century), but not a denial that such rates had ever been hypothesized.
We do not state anywhere in our paper that 2m or more of SLR by 2100 has been published as a peer reviewed and “informed estimate”. We do state that this has been ‘inferred’ and ‘argued’ as a “viable 21st century scenario”. We believe there is value in constraining the upper limits to the role of ice dynamics in future SLR. And, from what we know about historical rates of SLR in conjunction with what ‘we know we don’t know’ about ice dynamics, we believe it is reasonable to ponder very high rates of SLR in the next century. However, we also believe that it is problematic to project such a ‘hypothesis’ as a supported theory without proper testing by the scientific method. The question raised by RC is whether or not this hypothesis has circulated within the scientific community.
In his 2007 paper (Environ. Res. Lett. 2(2007)) Hansen proposes a rate of sea level rise of “5 m this century.” This is hypothetical, but he is confident that it is a “far better estimate than a linear response”. This is accompanied by his statement that he finds it “almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale.” The provisional nature of his discussion is irrelevant; it is an explicit statement that 5 m of sea level rise in this century is a possibility he regards as viable, published in the scientific literature by the person who is arguably (and deservedly) the most visible and authoritative climate scientist in the world. No reader of this paper would assume that Hansen didn’t actually mean what he said. Hansen reinforced this idea in other publications and statements, including in his briefing to Congress on 23 June 2008 (“sea level rise of at least two meters is likely this century”). Our analysis specifically tested the likelihood of next-century sea level rise of more than 2 m, and Hansen explicitly hypothesized 5 m of sea level rise in this century.
Hansen has gone on record with specific numbers, but other published studies including the 2006 Overpeck and Otto-Bliesner Science papers left the upper limit open ended, and certainly implied it could be quite high. The fact that this idea was present in the scientific community was confirmed for us by 8 scientific presentations we gave on this topic in the past year (5 in the US, including the Fall 2007 AGU and 3 in Europe). At none of those talks did anyone in the audience question what high forecasts we were referring to. The comments we got back on our work were overwhelmingly positive, and were along the lines that what we had presented was a good next step – both to move past the IPCC’s low sea level forecasts, and as a response to the persistent hypotheses of very high rates of sea level rise that were circulating. Criticisms, where they were voiced, were largely that we were underestimating the power of dynamics and that rates of sea level rise well in excess of 2 m/century might occur in spite of our conclusions.
We agree that the media coverage of our paper (as well as others before it) has undesirable side effects. Wherever we had the opportunity we pressed media writers not to use terms like “exaggerated” or “high sea level forecasts debunked,” and we have consistently stressed that our results indicate a very significant sea level rise and are no justification for any kind of complacency. We have stressed that even our low end scenario of 0.8 m of SLR would have tremendous consequences. However, we stand by our statements that sea level rise at rates of substantially more than 2 m this century were in fact put forward as a likely possibility.
Earlier this summer Andy Revkin published a piece in the New York Times about what he has termed the “Whiplash Effect”: confusion created in the public mind by media coverage of rapidly evolving scientific ideas. There has certainly been some whiplash in this case. However it is others who cracked the whip. We have simply refused to let go of the other end.
Mark in SF writes:
It is blindingly obvious.
#83 and #90 – Richard and Dave, thanks for that. I get the logic and agree with it. It would so help if RC would just come out and say it though!
Come on, tell me – does the article Target CO2 at https://www.realclimate.org/index.php/archives/2008/04/target-co2/ say this or not (also look at #18 there)? Am I being pedantic here? I think it stops short, and a target – however qualified – needs to be made much more explicit from RC’s contributors. At the moment, even many NGOs aren’t heading for
Steve you have referred to the Howat paper a number of times noting that the smaller glaciers are providing more output than the largest glaciers. First of all the study is focussed mainly on southeast Greenland glaciers. Secondly our attention has been focussed first on the largest glaciers which makes sense. This paper follows on the heels of another paper I have noted on thinning of marine terminating outlet glaciers. What both papers show is that the thinning and acceleration and consequent ice loss is widespread, and not just associated with a few glaciers. Given this it should not be surprising that the smaller marine terminating outlet glaciers that all do drain the ice sheet, can provide an important volume of ice. It should be noted that this is the point of Howat et al., they are not trying to make the point that the smaller glaciers are more important, as they were not comprehensive in examining all glaciers. But it is key to show that it is marine terminating glaciers that have accelerated and small ones too. With respect to the Jokulhlaup you cite, this paper does not cause an issue with our understanding of the ice sheet. They did not identify a specific frictional melting component. They state the remainder is from frictional melting of the actual subglacier drainage and base flow, without tyring to break that down, which would be impossible in their case. The point is base flow could have and probably was the bigger source. The main weakness I see in the Pfeffer et al, paper is that they do not take advantage of the very latest work to articulate that it is accleration of marine terminating outlet glaciers due to force inbalance that is causing the primay sea level change for the GIS, and not the meltwater lubricating effect that many have confused as a prime contributor. In fact immediately after the release of the paper one of the authors was quoting invoking the now dead notion of the Zwally effect, that is enhanced meltwater lubrication being the key to ice accleration, as the main reason for acceleration.
Hey everybody,
Check out this excellent interview about the arctic with Dr. Walt Meier of NSIDC.
http://wattsupwiththat.com/2008/09/21/nsidc-s-dr-walt-meier-answers-10-questions/#more-3188
Dill Weed
#98
Steve,
Thank you for the link.
> wattsup
Take your game card: http://timlambert.org/2005/04/gwsbingo/
> invoking the now dead notion of the Zwally effect,
> that is enhanced meltwater lubrication being the
> key to ice accleration
Mauri, is this notion dead globally, or for specific conditions? I keep seeing mention of flow under ice in Antarctica, and am wondering if you refer to Greenland conditions or to a more basic understanding of ice flow globally. Pointer welcome, glad to read more. I’m assuming getting these issues solved is going to be major decision for the next IPCC report.
I’m also curious if there is any anticipated tally of research that will be coming with the conclusion of the International Polar Year and the ANDRILL and other large projects. I realize the huge amount of data constrains what can be written up and how quickly.
__________________
ReCaptcha: support advised
!!
More opportunities for data collection (where glaciers are cold at the base, at least):
Multiple generations of interglacial lake sediment preserved beneath the Laurentide Ice Sheet
Author(s): Briner JP, Axford Y, Forman SL, Miller GH , Wolfe AP
GEOLOGY Volume: 35 Issue: 10 Pages: 887-890 OCT 2007
DOI: 10.1130/G23812A.1
Abstract: … beneath portions of the northeastern Laurentide Ice Sheet, characterized by cold-based glaciation, sediment sequences representing multiple interglaciations have been preserved within extant lake basins. Radiocarbon and optically stimulated luminescence dating confirm the antiquity of the sediments, thereby extending the terrestrial paleoenvironmental record of the Canadian Arctic by hundreds of thousands of years. The lake sediment record presented here corroborates numerous recent cosmogenic exposure dating studies indicating complex patterns of erosion beneath polar ice sheets. It also demonstrates that the presence of intact interglacial sediments does not demand unglaciated refugia. Similarly ancient sediments may be preserved in many regions formerly covered by Pleistocene ice sheets.
Guy on “Target CO2” paper (multiple),
I’ve been lurking for several months.
In June I took the current draft of that paper as my starting point to get into current climate science: Start with Hansen, start with the most credible worst-case scenario or lowest-CO2 target proposed, work backwards to see how well supported. Could consequences of 21st century warming really be a lot more dire than in IPCC AR4? I obtained and read 34 of the 89 papers referenced in “Target”, plus another twenty or so further papers referenced in those 34, with a slight emphasis on the Last Interglacial (LIG) as a model for what’s certainly in store under BAU, though it’s very uncertain how long that will take. Plus other papers on Hansen’s website.
I sympathize with your frustration: “Target” makes a compelling case that we really have to get CO2 down to 350 or below, but most of the IPCC and policy discussion hovers around 450-500 – so who is “right”? While non-SLR consequences like drought, flooding, crops, ecosystem migration and species loss look bad enough, 2m or more sea level rise should be the most dramatic, a good place to focus attention. Ice flow dynamics have to matter a lot, and the IPCC’s 80cm doesn’t include them. However long it took, sea level was 4-6m higher during the LIG, with global mean temperature only 1C or so warmer, and CO2 100 ppm or so less than today’s.
The Pfeffer paper is helpful, putting plausible constraints on the speed of ice discharge. It’s not the last word, as Gavin notes, but further refinements (which could be higher or lower than 2m by 2100) await more science at both GIS and WAIS, glacier physics, and more comprehensive glacier modeling, which simply requires more time. RC and the other climate scientists cannot say definitively whether Hansen is “right” about 350; rather, I imagine, they’re working as hard as they can to refine the science and the models, and they will be for years.
I’m concerned there is too much focus on 2100, or only looking at the “next 100-150 years”, presumably because most people just can’t handle worrying about farther ahead. With all the latencies in ocean heat content and other parts of that “pipeline”, 450 ppm or higher is guaranteed to put us back in the Last Interglacial, at 4-6m higher sea level within centuries to a few millennia. The only protection against that would be – at some point – getting CO2 levels back down around 280-300 ppm. So at some point in time Hansen’s 350 almost has to be an upper limit, as he says.
Even if SLR is “only” +1-2m by 2100, if we get to that point with 400 ppm or more CO2, we’re probably also locked in to +2-4m by 2200. Most people are aware of places and events 2000 years ago, and a lot of history in between. Maybe they would respond to arguments about a business-as-usual world of 2200, 2500, 4000 AD.
Re 99. Gavin, you do now I don’t make predictions. You do know I always stress the uncertain future. You do know I (almost) always refer to peer-reviewed studies.
You do know the oceans release heat daily, weekly, seasonally, and in various oscillations and cycles, etc. You do know, too:
“…Observational and computational progress in physical oceanography, however, over the last 30 years has rendered obsolete the old idea that the fluid ocean is a slowly changing, passive, almost geological system. Instead, it is a dynamically active, essentially turbulent fluid, in which large-scale tracer patterns arise from active turbulence and do not necessarily imply domination of the physics and climate system by large-scale flow fields….”
Ref: Wunsch, Carl, 2007. The Past and Future Ocean Circulation From a Contemporary Perspective. Chapter in Schmittner, Andreas, John Chiang, Sidney Hemmings, Editors, 2007. Ocean Circulation: Mechanisms and Impacts. AGU Geophysical Monograph Series Vol. 173, 2007, online http://ocean.mit.edu/~cwunsch/papersonline/present_pastocean_rev_2april.pdf
Well, I see misprint ‘2’ instead of ‘1’ in my quick writing, please see:
“North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.”
Ref: Keenlyside, N.S., M. Latif, J. Jungclaus, L. Kornblueh, and E. Roeckner, 2008. Advancing decadal-scale climate prediction in the North Atlantic sector. Nature Vol. 453, No 7191, pp. 84-88, May 1, 2008
You do know I always say, it remains to be seen…
[Response: Picture Timo talking to Galileo as he is walking up the Tower of Pisa with his wooden and lead balls:
Galileo: I predict that when dropped at the same time, the balls will hit the ground after an equal amount of time.
Timo: But have you seen this paper on the wind?
Galileo: I’m assuming that the winds are a negligible effect.
Timo: But what about the uncertainties in time-keeping apparatus – Here’s a paper about clocks drifting.
Galileo: Obviously I am only talking about time differences that detectable with current technology.
Timo: here’s another paper about variations in the gravity field across the planet, and here’s one about the impact of operator error in ball dropping stations, and here’s another on cosmic ray impacts on small round objects in the air.
Galilieo: None of those things are relevant.
Timo: Well, all I’m saying is that we’ll have to wait and see.
Galileo: Hmmm…. (drops balls and they both land at the same time)… See, I was right.
Timo: Here’s a paper on the non-reproducibility of ball dropping experiments.
Galileo: Sigh…..
– gavin]
Re #104: That’s a nice try by Walt, meaning that his information is, um, sea ice off a polar bear’s back as far as the regular commenters there are concerned. I assume the hope is that many of those who read but do not comment are less set in their ways.
This is a good place to mention some recent results (WaPo story here, paper here) finding that conservatives (however defined) have an internal dialog such that when they hear information refuting one of their beliefs they tend to become *more* confirmed in it. This effect is not apparent among other segments of society. I notice that one of the authors has a quite active blog.
While I’m at it, and also relevant to some of the other discussion above, this paper (“Are debatable scientific questions debatable?“) is good advice (abstract):
“Scientists often find difficulty in engaging in formal public debate about transcientific social issues. Although science is a highly disputatious institution, public argumentation amongst scientists follows very different conventional practices from those that rule in political and legal arenas. Amongst other differentiating features, scientific disputes are typically conducted in writing rather than orally, they are not sharply polarised or formally adversarial, they are seldom addressed to a specific proposition, and they do not reach decisive closure. As a result, the rhetorical style that scientists learn from participation in such practises is not well adapted to the established format of socio-political ‘debate’. For scientists to contribute effectively to such debates, they must learn new ways of making their particular type of knowledge convincing in unfamiliar intellectual and social contexts.”
Finally, since I feel compelled to complete the trifecta, there’s this paper (“Understanding Public Complacency About Climate Change: Adults’ mental models of climate change violate conservation of matter“) finding that a substantial majority of intelligent humans (the group studied was MIT grad students) have no grasp of stock and flow.
to John Mashey #61 and Joseph O’Sullivan #84
I know that 6ft would probably be a big deaL, I as trying to visualize how big given that I live in the city as well. The map application Mashey referenced is the google widget I was thinking of, but I was wondering if anyone had links to more accurate readings than that.
Joseph, I was thinking at what point does the Financial District become like Venice? Pumping out the subway is bad enough as it is. I was wondering at what point do we have to retrofit some tunnels or maybe restore the old tracks on the Brooklyn Bridge, and maybe add them to the Queensboro (which strike me as more feasible projects). I like underground as much as the next guy, but going back to El trains may be necessary in many areas.
#111
Jess,
OK, you have upgraded NYC, including all the underground electrical and communications utilities.
What are you going to eat?
A SLR of six feet is enough to take out much of the fuel, fertilizer and pesticide production facilities used by modern agriculture. Thus, you not only have to find the capital to upgrade NYC but also much of the petrochemical industry on the Gulf Coast.
What are you going to wear? Most modern fiber is made near current sea level.
These days everything has a computer chip in it. Where is the plastic used to make the carrier for that computer chip made? Near sea level. Where is your shampoo made? And, the bottle it is shipped in?
And, out here in California where we grow some of the food of the food that NYC eats, it would not take much of a SLR to knock out the water supplies for irrigation and our drinking water.
It will be expensive for NYC to maintain its lifestyle. Of course, you are lucky, your airport is a couple of feet higher than SFO or OAK.
Any of these is fixable. However, if they come faster than we expect or they come all at the same time, then we are going to be in over load mode.
Steve (110), the 3rd referenced study concluded that highly educated (including in the sciences) people have some mental abnormality that does not permit them to understand that a net positive inflow increases stuff at hand. This being the only way the researchers could explain the subjects’ seeming dichotomy in their comprehension of AGW in its entirety. I find that incredibly pedantic, short-sighted, and ludicrous prima facie.
Your 2nd referenced study presents some cogent and significant observations that affect the scientist operating in the non-scientific world.
But I find the contention in 1st reference that only “conservatives” dig in when challenged equally silly prima facie.
More melt-down problems for Wall Street? I just happened across this (still in press, I believe):
Yin, J., M. E. Schlesinger, and R. J. Stouffer, 2008:
Rapid sea level rise threatens the Northeast Coast of the United States. Nature. 8/08.
Abstract: “Human-induced climate change could cause sea level rise (SLR) and slow down the Atlantic meridional overturning circulation (MOC). Low-lying Florida and western Europe are often evoked as the vulnerable regions to these changes. Here based on a state-of-the-art climate model, we report a rapid SLR on the northeast coast of the U.S. during the 21st century. The rapid SLR is projected under various IPCC greenhouse-gas (GHG) emission scenarios including low, medium and high rates. A dynamic (relative to the geoid) SLR induced by the weakening of the MOC is imposed on the global steric (density-dependent) and eustatic (mass-dependent) SLRs, thereby greatly enhancing the SLR rate on the northeast coast of the U.S. The future changes of sea level and ocean circulation therefore pose a great and imminent threat to this heavily populated area.”
It doesn’t say how much, unfortunately.
Re #113: Rod, I would expect that a conservative denialist would find both of those results objectionable in the extreme. Do keep digging, though.
There was a question asked up-thread about ocean acidification, and serendipitously a new paper has just appeared (press release pasted below). Pertinent to another topic these results seem quite consistent with Hansen’s call for 350 ppm, noting the finding that “even if atmospheric CO2 stabilizes at the current level of 380 ppm, fewer than half of existing coral reef will remain in such an environment.” Putting things in a context of “avoidig dangerous climate change” (referring to the UNFCCC) is also consistent with Hansen’s approach.
————————–
Modest CO2 cutbacks may be too little, too late for coral reefs
Stanford, CA—How much carbon dioxide is too much? According to United Nations Framework Convention on Climate Change (UNFCCC) greenhouse gases in the atmosphere need to be stabilized at levels low enough to “prevent dangerous anthropogenic interference with the climate system.” But scientists have come to realize that an even more acute danger than climate change is lurking in the world’s oceans—one that is likely to be triggered by CO2 levels that are modest by climate standards.
Ocean acidification could devastate coral reefs and other marine ecosystems even if atmospheric carbon dioxide stabilizes at 450 ppm, a level well below that of many climate change forecasts, report chemical oceanographers Long Cao and Ken Caldeira of the Carnegie Institution’s Department of Global Ecology in the journal Geophysical Research Letters.
The researchers’ conclusions are based on computer simulations of ocean chemistry stabilized at atmospheric CO2 levels ranging from 280 parts per million (pre-industrial levels) to 2000 ppm. Present levels are 380 ppm and rapidly rising due to accelerating emissions from human activities, primarily the burning of fossil fuels.
This study was initiated as a result of Caldeira’s testimony before a Congressional subcommittee on Fisheries, Wildlife and Oceans in April of 2007. At that time he was asked what stabilization level would be needed to preserve the marine environment, but had to answer that no such study had yet addressed that question. Cao and Caldeira’s study helps fill the gap.
Atmospheric CO2 absorbed by the oceans’ surface water produces carbonic acid, the same acid that gives soft drinks their fizz, making certain carbonate minerals dissolve more readily in seawater. This is especially true for aragonite, the mineral used by corals and many other marine organisms to grow their skeletons. For corals to be able to build reefs, which requires rapid growth and strong skeletons, the surrounding water needs to be highly supersaturated with aragonite.
“Before the industrial revolution, over 98% of warm water coral reefs were surrounded by open ocean waters at least 3.5 times supersaturated with aragonite” says Cao. “But even if atmospheric CO2 stabilizes at the current level of 380 ppm, fewer than half of existing coral reef will remain in such an environment. If the levels stabilize at 450 ppm, fewer than 10% of reefs would be in waters with the kind of chemistry that has sustained coral reefs in the past.”
For the ecologically productive cold waters near the poles, the prospects are equally grim, says Cao. “At atmospheric CO2 levels as low as 450 ppm, large parts of the Southern Ocean, the Arctic Ocean, and the North Pacific would experience a rise in acidity that would violate US Environmental Protection Agency water quality standards.” Under those conditions the shells of many marine organisms would dissolve, including those at the base of the food chain.
“If current trends in CO2 emissions continue unabated,” says Caldeira, “in the next few decades, we will produce chemical conditions in the oceans that have not been seen for tens of millions of years. We are doing something very profound to our oceans. Ecosystems like coral reefs that have been around for many millions of years just won’t be able to cope with the change.”
“When you go to the seashore, the oceans seem huge,” he adds. “It’s hard to imagine we could wreck it all. But if we want our children to enjoy a healthy ocean, we need to start cutting carbon emissions now.”
On the topic of a “shutdown” of the “thermohaline circulation,” I’d be interested in seeing a post that summarizes the current thinking. The Lenton et al “Tipping Elements” paper from earlier this year puts more emphasis on it than AR4.
http://www.pnas.org/content/105/6/1786.full.pdf
Just wondering what Realclimate’s thoughts are on this topic.
#108 – Srooke, thanks so much for your contribution – and sympathies! And I totally agree with timescales – most climate science projections stop at 2100, leading to this bizarre logical fallacy among the media at least that EVERYTHING stops there! If SLR and temperature are both still rising by then, the game is surely up. And what ethical gounds are there for caring less about the world after 2100? I understand a reduced emotional response, but that has no moral or intellectual authority. If our actions today only cataclysmically affect people in 400 years time, that’s a real problem in terms of galvanising a response.
I understand the ever increasing problem of probabilities beyond 2100, but if we are at that point in a world beyond the possibility of any human intervention, this point does need re-inforcing.
And I also sympathise with the problem of not knowing enough re the 350ppm target. And yet Hansen has weighed in, and policies have to be forged by December 2009, so waiting for more data before saying anything at all isn’t really an option. A simple “that seems a reasonable conclusion on the basis of available evidence” (or not!) from colleagues would massively help.
12 attempts at a Real Climate specific response to 350ppm in 14 days! I promise I won’t throw my toys out of the pram or be rude, but I must keep asking…
The Independent in the UK is leading with this – http://www.independent.co.uk/environment/climate-change/exclusive-the-methane-time-bomb-938932.html
Highlights:
Exclusive: The methane time bomb
The first evidence that millions of tons of a greenhouse gas 20 times more potent than carbon dioxide is being released into the atmosphere from beneath the Arctic seabed has been discovered by scientists.
The Independent has been passed details of preliminary findings suggesting that massive deposits of sub-sea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats.
In the past few days, the researchers have seen areas of sea foaming with gas bubbling up through “methane chimneys” rising from the sea floor. They believe that the sub-sea layer of permafrost, which has acted like a “lid” to prevent the gas from escaping, has melted away to allow methane to rise from underground deposits formed before the last ice age.
They have warned that this is likely to be linked with the rapid warming that the region has experienced in recent years.
Orjan Gustafsson of Stockholm University in Sweden, one of the leaders of the expedition, described the scale of the methane emissions in an email exchange sent from the Russian research ship Jacob Smirnitskyi.
“We had a hectic finishing of the sampling programme yesterday and this past night,” said Dr Gustafsson. “An extensive area of intense methane release was found. At earlier sites we had found elevated levels of dissolved methane. Yesterday, for the first time, we documented a field where the release was so intense that the methane did not have time to dissolve into the seawater but was rising as methane bubbles to the sea surface. These ‘methane chimneys’ were documented on echo sounder and with seismic [instruments].”
At some locations, methane concentrations reached 100 times background levels. These anomalies have been seen in the East Siberian Sea and the Laptev Sea, covering several tens of thousands of square kilometres, amounting to millions of tons of methane, said Dr Gustafsson. “This may be of the same magnitude as presently estimated from the global ocean,” he said. “Nobody knows how many more such areas exist on the extensive East Siberian continental shelves.
The preliminary findings of the International Siberian Shelf Study 2008, being prepared for publication by the American Geophysical Union, are being overseen by Igor Semiletov of the Far-Eastern branch of the Russian Academy of Sciences. Since 1994, he has led about 10 expeditions in the Laptev Sea but during the 1990s he did not detect any elevated levels of methane. However, since 2003 he reported a rising number of methane “hotspots”, which have now been confirmed using more sensitive instruments on board the Jacob Smirnitskyi.
Apparently ocean acidification will affect more than just shells (excerpt from a post on the blog of EPOCA — the European Project on Ocean Acifification):
“Rising acidification of the ocean could reduce fertilisation of marine invertebrates and might eventually wipe out colonies of sea urchins, lobsters, mussels and oysters, according to a study.
“Scientists knew that ocean acidification was eating away at the shells of marine animals, but the new study has found that rising acidity hindered marine sperm from swimming to and fertilising eggs in the ocean.”
119 Guy, the quote of methane strength is wrongish. Methane degrades at a fairly constant total amount, not a constant percent. Thus, double methane concentrations, and the half-life of methane doubles. Since methane is so powerful (I’ve searched but never found an instantaneous strength of CH4 VS CO2), this could change the 100 year multiplier from 23 (as it is currently) to 100 PDQ. Yet another non-linear response of a non-linear response of a linear input.
[Response: The effect is real, but it isn’t as strong as you suggest. Calculations in Table 1 in Schmidt and Shindell (2003) suggest you need to multiply concentrations by a factor of 10 to get a doubling of the lifetime. – gavin]
118 A new paper from the Tyndall Centre suggests that we are heading for 650 ppm.
http://www.tyndall.ac.uk/media/news/latest_news.shtml
Add in the methane belching (post 119) from the East Siberian and Laptev Seas and 650 ppm may be on the low side.
Re 117 ccc, please see
Zickfeld, Kirsten, Anders Levermann, M. Granger Morgan, Till Kuhlbrodt, Stefan Rahmstorf, and David W. Keith, 2007. Expert judgements on the response of the Atlantic meridional overturning circulation to climate change. Climatic Change Vol. 82, No 3-4, pp. 235-265, June 2007
Abstract
We present results from detailed interviews with 12 leading climate scientists about the possible effects of global climate change on the Atlantic Meridional Overturning Circulation (AMOC). The elicitation sought to examine the range of opinions within the climatic research community about the physical processes that determine the current strength of the AMOC, its future evolution in a changing climate and the consequences of potential AMOC changes. Experts assign different relative importance to physical processes which determine the present-day strength of the AMOC as well as to forcing factors which determine its future evolution under climate change. Many processes and factors deemed important are assessed as poorly known and insufficiently represented in state-of-the-art climate models. All experts anticipate a weakening of the AMOC under scenarios of increase of greenhouse gas concentrations. Two experts expect a permanent collapse of the AMOC as the most likely response under a 4×CO2 scenario. Assuming a global mean temperature increase in the year 2100 of 4 K, eight experts assess the probability of triggering an AMOC collapse as significantly different from zero, three of them as larger than 40%. Elicited consequences of AMOC reduction include strong changes in temperature, precipitation distribution and sea level in the North Atlantic area. It is expected that an appropriately designed research program, with emphasis on long-term observations and coupled climate modeling, would contribute to substantially reduce uncertainty about the future evolution of the AMOC.
Further:
Drijfhout, Sybren S., W. Hazeleger, F. Selten and R. Haarsma, 2008. Future changes in internal Atlantic Meridional Overturning Circulation variability. Climate Dynamics Vol. 30, No 4, pp. 407-419, March 2008, online http://www.knmi.nl/publications/fulltexts/climdyn08.pdf
Abstract
The response of the internal variability of the Atlantic Meridional Overturning Circulation (MOC) to enhanced atmospheric greenhouse gas concentrations has been estimated from an ensemble of climate change scenario runs. In the model, enhanced greenhouse forcing results in a weaker and shallower MOC with reduced internal variability. At the same time at 55°N between 0 and 1,000 m the overturning increases as a result of a change in the area of convection. In a warmer world, new regions of deepwater formation form further north due to the poleward retreat of the sea-ice boundary. The dominant pattern of internal MOC-variability consists of a monopole centered around 35°N. Due to anthropogenic warming this monopole shifts poleward. The shift is associated with a stronger relation between MOC-variations and heat flux variations over the subpolar gyre. In old convective sites (Labrador Sea) convection becomes more irregular which leads to enhanced heat flux variability. In new convective sites heat flux variations initially are related to sea-ice variations. When the sea-ice coverage further decreases they become associated with (irregular) deepwater formation. Both processes act to tighten the relation between subpolar surface heat flux variability and MOC-variability, resulting in a poleward shift of the latter.
Re: 121: Methane lifetime is a function of the oxidative capacity of the atmosphere (namely, hydroxyl radical abundance).
Indeed, increased methane emissions lead to decreased hydroxyl concentrations, but it isn’t a straightforward calculation to determine exactly how much hydroxyl disappears, or how much methane lifetime increases due to that. Also, other factors effect hydroxyl concentrations: NOx emissions, for example.
Note that increased methane also leads to increased ozone concentrations, for added radiative forcing bang for your methane buck.
The last time I looked up comparative methane and CO2 forcings, I found a ratio of 21 (methane:CO2) by molecule or a ratio of 60 (methane:CO2) by mass.
12 attempts at a Real Climate specific response to 350ppm in 14 days! I promise I won’t throw my toys out of the pram or be rude, but I must keep asking…
And I shall keep asking, has it ever occured to you to do your own research, instead of demanding that others do it for you? Science is about discovery, previously unknown phenomenon become revealed, previously unanswered questions become reasonable, revealing more questions.
After a while, the constant nagging gets tiresome. Clearly we want to reduce atmospheric carbon dioxide concentration, once we have that ability, the final equilibrium number is pretty much meaningless, call it anything around 300 ppm or so. 350 is probably a little on the high side. Captcha : track esperanto
#122 – that Tyndall paper is terrifying. I guess that’s why Hansen says coal phase-out is the only possible way…
[All: I’ve closed comments for now, as I can’t keep up with responses. More discussion can continue in response to the next post on sea level rise. –eric]