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How much future sea level rise? More evidence from models and ice sheet observations.

Filed under: — eric @ 26 March 2006

Lots of press has been devoted to four papers in this week’s Science, on the topic of ice sheets and sea level.

We’ve already discussed the new evidence that Greenland’s glaciers are speeding up. What is new this week is an effort to evaluate the impact of future warming on Greenland by looking at what happened to it last time it got very warm — namely during the Last InterGlacial (LIG) period, about 125,000 years ago. The same group of authors looked at this in two ways, using NCAR’s Community Climate System model (CCSM) coupled to a state-of-the-art 3-D ice sheet model.

First, in a paper by Otto-Bliesner et al. they ran simulations for the Last Interglacial, and took a look at what happened to the ice sheets. They find that most of the icefields in Arctic Canada and Iceland disappear, and that the Greenland ice sheet is reduced to a steep ice dome in central and northern Greenland. These results are in very good agreement with the available ice core and other paleoclimate data evidence, which indeed show that the Canadian ice sheets disappeared during the LIG, and strongly suggest that much of southern Greenland was deglaciated.

Second, in a paper by Overpeck et al., they examine the implications for past and future sea level rise. The results show that the Greenland and other Arctic ice sheets probably did not contribute more than 3.4 m to the LIG sea level rise. However, data from coral reefs exposed above sea level today, and other evidence, point to an LIG sea level at least 4 m and possibly as much as 6 m greater than today. This suggests that the balance came from the Antarctic ice sheet. This is turn implies a strong sensitivity of the Antarctic ice sheet to sea level rise and climate warming — an idea that goes back to John Mercer (1976) but that had until recently fallen out of favor in much of the glaciology community.

Projecting forward in time, the implication is that our future will also see 4-6 m of sea level rise, and that — given the recent evidence for accelerated flow of both Greenland and Antarctic glaciers — this may occur much faster than we expect. In the model simulations, Greenland may already be warmer in 2100 than it was at the height of the LIG. The rate of sea level rise associated with the warming into the last interglacial was probably greater than 10 mm/yr* while current sea level rise is roughly 3 mm/yr. To the extent that the LIG is a good analog for our future, sea level rise is therefore rather likely to accelerate.

Also in this week’s Science are two articles that further strengthen the case that ice sheets are quite sensitive to warming climate. A paper by Göran Ekström et al. shows that the increased speed of Greenland glaciers occurs in distinct lurches (observed as micro “ice-quakes”) that are strongly seasonal, with the greatest number occuring in late summer. This provides evidence that meltwater plays an important role in the acceleration of Greenland’s glaciers. Essentially, the idea is that surface melting that occurs in the summer can make its way quickly down to the glacier bed, lubricating the bed and allowing the glaciers to slide more rapidly. The “ice quakes” occur because the rough bedrock surface causes the glaciers to stick; they only accelerate when enough hydraulic pressure has built up to help float the glacier over the bumps. This is strong evidence that climate, not merely “internal ice sheet dynamics”, has contributed to the recent increases in Greenland’s glaciers. Indeed, a doubling of the rate of quakes has occurred over the past five years, just as the aerial extent of surface melting has increased.

Finally, in a very nice bit of work Velicogna and Wahr use data from the “Gravity Recovery and Climate Experiment” (GRACE) satellites to show that the Antarctic ice sheet has been losing mass at a rate of 150 +/- 80 km3 each year since 2002. That’s equivalent to about 0.4 mm of sea level rise each year. This is about twice other recent estimates, while IPCC 2001 actually gives negative 0.1 mm/yr. What is especially nice about Velicogna and Wahr’s study is that by using gravity measurements they have measured mass changes directly, avoiding the problem of virtually all previous measurements of ice sheet mass change, which usually measure either input (snowfall) or loss (calving, melting, or thinning of the ice), but not both at once.

What does all this news mean in practice? Reading the editorials in Science, and quotations from various researchers in newspaper articles, one might be under the impression that we should now expect “catastrophic sea-level rise” (as Science’s Richard Kerr writes). Of course, what is catastrophic to the eye of a geologist may be an event taking thousands of years. In the Otto-Bliesner et al. simulations, it takes 2000-3000 years for Greenland to melt back to its LIG minimum size. And while we don’t advocate sticking with the typical politician’s time frame of 4 or 5 years, the new results do not require us to revise projections of sea level rise over the next century or so. This is because even with Arctic temperature continuing to rise rapidly, there will still be significant delay before the process of ice sheet melting and thinning is complete. There is uncertainty in this delay time, but this is already taken into account in IPCC uncertainty estimates. It is also important to remember that the data showing accelerating mass loss in Antarctica and rapid glacier flow in Greenland only reflect a very few years of measurements — the GRACE satellite has only been in operation since 2002, so it provides only a snapshot of Antarctic mass changes. We don’t really know whether these observations reflect the long term trend.

On the other hand, none of the new evidence points in the direction of smaller rates of sea level rise in the future, and probably nudge us closer to the upper end of the IPCC predictions. Those who have already been ignoring or naysaying those predictions now have even less of a leg to stand on. Coastal managers, real estate developers, and insurance companies, at the least, would be wise to continue to take such predictions seriously.** As Don Kennedy and Brooks Hanson write in the lead Editorial, “accelerated glacial melting and larger changes in sea level should be looked at as probable events, not as hypothetical possibilities.”

———
*Note that we don’t actually have good constrains on the rate of sea level rise from the penultimate glacial period (~140,000 years ago) to the last interglacial (LIG, ~125,000 years ago). However, we have very good data on the more recent glacial-to-interglacial transition, between about 14,000 and 7,000 years ago. During that time, sea levels rose at an average rate of about 11 mm/year, and at rates much higher than that for short intervals.
**Consider for example, that 1 m of sea level rise would change the frequency of what are now 100-year floods in metropolitan New York to once in every four years events. (See here and Rosenzweig, C. and W.D. Solecki (Eds.). 2001. Climate Change and a Global City: The Potential Consequences of Climate Variability and Change – Metro East Coast (MEC). Report for the U.S. Global Change Research Program, National Assessment of the Potential Consequences of Climate Variability and Change for the United States, Columbia Earth Institute, New York. 224 pp)


87 Responses to “How much future sea level rise? More evidence from models and ice sheet observations.”

  1. 51
    llewelly says:

    Re 46: Closest I can find is everyone’s favorite moulin shot . (it’s the pic on the right – click to enlarge). It looks like a waterfall, and there are people around it, and it was taken on Greenland’s ice sheet. But not on an ice shelf, and not precisely a waterfall…

  2. 52
    Alan says:

    Re #18

    I don’t understand your apparent grudge against environmentalists. How does “naming of scientific literature by environmentalists”, land the authour in “hot water”, would you rather they sourced the forest fairies?

    If the ultimate “job” of climate science is to predict climate, and you are willing to give weight to Jim Hansen’s timescale for averting climate change, why does investigating the environmantal impacts suddenly become a “fortune telling” exercise? ( Note: To the vast majority of punters and journalists who do not understand the scientific method, the difference between scientists and soothsayers is based on an individuals notion of common-sense. )

    I will whole-heartedly agree that we do not have the ability to predict next years global harvest but ever since humans started planting seeds and milking cows we have come up with more accurate and better educated “guesses”. One thing has not changed in 10,000yrs of agriculture, when our “guess” is seriously wrong, civilization goes out the window and we starve.

    Turning a deaf ear to environmental groups is just as foolhardy as turning a deaf ear to fossil fuel advocates. Both groups have their dogma and both groups make plenty of dramatic assertions that have been investigated in a scientific manner. Doesn’t science itself progress by constantly finding ways to test the validity of popular, interesting, crazy, politically suicidal, blasphemous, scientific,,,assertions?

    Put another way, the concept of black holes floating around in the cosmos started with a geologist in 1783, it took at least 200yrs before anyone took the idea seriously and another 100yrs for us to find one!

  3. 53
    C. W. Magee says:

    Re 40.
    I thought that the agricultural CO2 theory had been disproved by Broecker’s demonstration of no -d13C anomaly prior to the industrial revolution.

  4. 54
    A Lincoln says:

    I would like to know your views, after having watching the recent BBC programme on the slowing and potentional ceasing/reversing of the gulf stream, what kind of effect this would have on the rising sea levels? Surely this would reverse the melting of the ice-caps, as it would encourage a new ice-age. All be it in a 100 years or so. What can we possibly expect to happen? As this would effectively give us a greater area of ice-cap, forming along the length of the British Isles and pack-ice around our own coast-line.

    [Response: Absolute cooling is extremely unlikely, a new ice age an impossibility, and very little impact on global sea level. See http://www.realclimate.org/index.php?p=159 - gavin]

    [It is further worth noting that the particular modeling experiments discussed in this post find that while Greenland meltwater does slightly affect the ocean circulation, even the very high rates of melting are insufficient to cause any cooling; at the most, they slow down the local rate of warming a little bit. Of course, more extreme scenarios can be imagined, with the glaciers accelerating even more. Since many of the important details of glacier dynamics are not well represented in the models yet, this can't exactly be ruled out on the basis of these experiments. But this is all very much in the realm of speculation. The likelihood of a new ice age as a consequence of global warming has been grossly exaggerated in both the popular media and the scientific literature. --eric]

    [Response: Eric, do you have any examples for the latter?
    Concerning sea level impacts, a paper on this is here. -stefan]

  5. 55
    pete best says:

    Re #18

    Environmentalists are potentially alarmist as they are in the world of politics and part of the free for all system of hype and hyperbole. It is not necessarily their fault, only hype gets peoples attention in the modern world, the press live and thrive on it. Science on the other hand cannot act that way and does not follow that method. Therefore scientists including Jim Hansen when they say things other than what they actually know are in the realm of speculation and conjecture even if it could end up being right.

    Contrary to popular scientific belief no black hole has ever been found. What has been shown is that taking relativity as gospel black holes can exist and may even exist but as yet none has been verified to exist. what has been shown is areas of space with massive gravitational strength but these could be one of a number of things and not necessarily a black hole.

    Climate science is complex and requires many variables in order to be able to predict second and third order effects such as the thermohaline systems faltering or the amazon drying out and releasing massive amounts of CO2. None is proven or has been shown to actually happen so we wait and try and predict with greater accuracy.

    Real climate is showing me personally just how complex climate is and we see very little here in the way of predicting or prophesizing doom and destruction for humanity.

    I sometimes wonder about the term “Abrupt” or “sudden” climate change as climate even under our deluge or fossil fuel burning is taking a long time to change (by human terms)radically enough to worry anyone in Government. Makes me wonder if there is a major scientific basis (younger dryas maybe but the cause is currently unknown)for it or is it a political tool.

  6. 56
    pete best says:

    #Re 54 Eric

    Does this mean that the thermohaline system in not in any present danger of stuttering or faltering at the present or near future time. Russian rivers increased discharge inot the atlantic, increased arctic ice melt and increased salinity and evaporation at the equator marked by increased freshness and precipitation at the poles which is increasing the flow rate of the thermohaline system (or so I have read) is not leading to issue with it at the present time and the recent measurements that showed a 1/3 slowdown in the flow rate were contentious at best ?

  7. 57
    KC Jones says:

    Thanks Chandler and llewelly, that’s the image I was after — the earthobservator.com version in particular. Awesome image.

  8. 58
    Paul says:

    Post #48 by John Monro:
    ===It will require an effort on behalf of mankind equivalent to fighting the Second World War, except this time no one has to die, be maimed or psychologically scarred for their whole life, nor do cities have to be destroyed or civilisations wrecked. We cannot leave this to people who seek to weigh the health of the world against these other considerations, there is no set of scales that can accomplish this measurement. But until we fully understand this moral imperative, the necessary action to deal with this issue will never, ever come. Sermon over.===

    That wasn’t a sermon John, but an example of Churchillian oration.
    Still, addressing AGW, just like any other issue, remains in the realm of public policy which requires the assent and support of the general public.

    And combatting AGW must we weighed against other considerations. The sacrifices that scientists are proposing are so radical, so drastic, and so costly that only the public can decide if it is a truly worthwhile battle.

  9. 59

    Re 58 Here is a sermon, or at least the views of the Archbishop of Canterbury, head of the Anglian Church.

    “And yet unless there’s a real change in attitude we have to contemplate those very unwelcome possibilities if we want the global economy not to collapse and millions, billions of people to die”.

    See http://news.bbc.co.uk/1/hi/sci/tech/4852136.stm

    Paul, I wonder whether you think saving billions of lives is a “truly worthwhile battle.”?

    Cheers, Alastair.

  10. 60
    David B. Benson says:

    Re #48 & #58: Regional climate change?

    Quotes from “Forest insects at epidemic levels”, Associated Press:
    COUR D’ALENE, Idaho — THe region’s largest infestation of mountain pine beetles in 20 years has hit more than a million acres of forests in northern Idaho and Montana, while 2.5 million acres in Washington face desease and insect problems. … But she said it would take several years of normal moisture for forests to return to health. … Mountain pine beetles have also been a problem in British Columbia, where at least 20 million acres of forest have been killed. Officials there say warmer-than-average winters have led to the outbreak.

  11. 61
    Florifulgurator says:

    Re 60: So, yet another positive feedback! We also have them beetles here in Bavaria. Spruce monocultures dying off.
    Re 58: O the immense sacrifices…
    Here´s a low-tech solution I currently ponder: Produce terra preta. Not slash&burn but slash&char them forests! Bury half of the char coal (=carbon sequestration plus valuable soil production), burn other half for energy plus refinery of the oils & methanol you get from wood pyrolysis.

    What do you experts think about that?

  12. 62
    Lynn Vincentnathan says:

    RE #58, AGW is not only a public realm issue, but ultimately a private realm issue. Each person has to decide whether or not to abate GW in his/her home, workplace, school, etc. As Hunter Lovins put it, “The national energy policy comes down to the cracks around your windows.”

    Since we in the rich world can actually save a lot of money, while saving the earth (I’ve reduced by more than 3/4 cost-effectively & save $100s every year), this should be a no-brainer. When will people reach down to pick up those $100 bills for their meager efforts at energy/resource efficiency/conservation? Are we so rich, gluttonous, and evil, that we would rather lose money & in the process kill people?

    But, of course, it is also a public issue at every level, from one’s town, state, country, & the world. It has to be addressed at all levels.

  13. 63
    Stewart Argo says:

    Re. 55:

    Contrary to popular scientific belief no black hole has ever been found. What has been shown is that taking relativity as gospel black holes can exist and may even exist but as yet none has been verified to exist. what has been shown is areas of space with massive gravitational strength but these could be one of a number of things and not necessarily a black hole.

    The theory behind black holes does a pretty good job of explaining what we see going on in the cosmos. Sure, the theory could be wrong – but until something better comes along, I’ll stick with black holes (If you’re aware of something that I’m not, please let me know).

    AGW does a pretty good job of explaining what’s happening to the planet. And until I see a credible alternative theory, I’ll stick with that as well.

    Falling into a black hole would provide some proof that it exists, but it would be pretty terminal for the observer. I don’t really want to take that chance with climate change.

  14. 64
    Hank Roberts says:

    Hosts, forgive the digression; Stewart, try this theory.

    Recent cite:
    http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:gr-qc/0511097

    Snippet from old 2001 news item:
    “… Emil Mottola of the Los Alamos National Laboratory in New Mexico and Pawel Mazur of the University of South Carolina in Columbia think gravastars are cold, dense shells supported by a springy, weird space inside. They’d look like black holes, lit only by the material raining down onto them from outside. In fact, they seem to fit all the observational evidence for the existence of black holes….”

  15. 65
    S Molnar says:

    Eric, I’m a bit confused about the magnitude of these icequakes in Greenland. You describe them as microquakes, and seem to view them as pretty insignificant, but news reports claim they are as big as magnitude 5 on the Richter scale. What’s the story? Are earthquake and icequake magnitudes incommensurate? Are the news reports wrong? I’ve been in magnitude 5 quakes, and I wouldn’t call them micro – just ask my dry cleaner.

  16. 66
    Mauri Pelto says:

    Based on monitoring these on Taku Glacier in Alaska most ice quakes are truly microquakes. In a glacier with a high velocity they occur very frequently. They can be caused by 1. Basal sliding events, which have a low frequency a short duration and no glacier surface signal. Calving events which are also low frequency, short duration but due have surface waves near the glacier front and the scariest when standing on a glacier nearby the source are surface crevassing events which are low frequency, short duration and provide a surface wave very close to the event on the glacier. Only a basal sliding event will trigger a seismic wave in bedrock.

  17. 67
    Ike Solem says:

    Famous modeller: “I wouldn’t want to fly in a modelled airplane. I’d worry to much about what was left out”.

    Of course, this doesn’t mean that models are worthless! There are always uncertainties in a science where the experimental options are extremely limited or non-existent. The papers described above seem to have taken the best possible approach in that they compare their models to a historical record; and of course a historical record is going to have more uncertainties then a real-time experimental observation.

    So, take the above estimate of 0.5 to 3 ft of water (all over the surface of the Earth’s oceans). Add a warmer ocean. Send a tropical disturbance out from Africa towards Florida. Do this enough times and eventually Miami get flattened – direct hit by a full-strength category 5. So, yes, there is cause for concern. There might be even more cause for concern since we are heading into a CO2 regime that hasn’t existed for millions of years, according to the detailed, peer-reviewed and published work of hundreds or thousands of full-time scientists.

    Note: Biofuels are a good idea. Building a coal-fired ethanol plant, on the other hand… no comment.

  18. 68
    pete best says:

    Re 63

    There have been recently some alternatives put forward to the notion of black holes but all present cosmology indicates that they do exist and are real cosmic phenomena.

    Global Warming is at present best explained by human induced fossil fuel burning but it is the consequences of that burning that concern me. I believe it to be true also but what we are discussing here is the environmental consequences and ramifications of that burning. At present according to the Keeling curve we are increasing the amount of CO2 in the troposphere by 2 ppm per annum. So by around 2040/50 we will have reached some 450 ppm and by 2100 it will be around 550 ppm. A doubling of pre industrial CO2 might happen and I personally believe that it will cause us a lot of issues but what those issues are are the issue.

    Is the Amazon going to dry out for instance, can it be shown to definitely be so ? Will the THC slowdown or become severely disrupted thus plunging Europe into colder and more frequently so winters ? Will rainfall change, will sea levels rise significantly ? Or will we just experience warmer weather and less and more rainfall depending on where we live.

    Indeed do we even have enough fossil fuels to make 550 ppm, we have plenty of coal but Oil and Gas are both getting towards their peak and alternatives need to be found before we experience an energy and transport crisis.

    For me at the present time the climate scientists are being ultra cautious and tell us that climate change is occuring, that it is human made but leave the impact of it to others to say and that makes for some extremely wild cliams to my mind anyway.

  19. 69
    Alan says:

    Re: #55 #63 #64 Off Topic, black holes DO exist…

    Quoting from the wiki link in my post…

    One of several definitions, I am using the general one…

    “The gravitational field is so strong that the escape velocity past its event horizon exceeds the speed of light.”

    And this is what I meant in the original post by the term “find one”…

    “…our own Milky Way. Sagittarius A* is now generally agreed to be the location of a supermassive black hole at the centre of the Milky Way galaxy. The orbits of stars within a few AU of Sagittarius A* rule out any object other than a black hole at the centre of the Milky Way assuming the current standard laws of physics are correct.”

    As we currently understand physics, what is inside the hole can never been seen so we will never observe the internal workings, we can also never directly observe the event horizon. No matter what is inside that region of space at the center of our galaxy, it will be forever known as a “black hole”.

    Off course, extreme skeptics can always come back with, “I doubt therefore I maybe!”

    [Response: No more black holes please. -gavin]

  20. 70
    pete best says:

    What I am trying to suggest is that there are people say who want everyone to sit up and take notice of climate change in order to get it at the top of the political agenda, to sell newspapers and magazines, to get the ratings up on the TV etc and there is what people who are peer reviewed say. The media has a responsibility to whatever it wants to, Science owns it to itself.

    Every climate computer model that fortells of doom is picked up on by the political lot and told as if it is gospel and it will happen. The peer reviewed mob on the other hand tell us within their sphere of influence/expertise what is happenning such as CO2 levels rising and correlating that to rising global temperatures etc. But it is a big leap to suddenly link beetles ravaging forests in Canada to climate change of humans doing although personally I do believe this sort of thing is related to human induced climate change but lots of people do not as yet thought seemingly the holistic systemic nature of climate change does make for some wild claims it is also right in many ways.

    One burning question is the acidification of the Oceans via increased CO2 absorbtion. http://www.physorg.com/news11008.html. This sort of thing worries me as second order effects in the systemic view (GAIA) of Earth.

  21. 71
    Lynn Vincentnathan says:

    There’s the other side to the sea level rise issue — the glaciers that are melting that in part lead to such a rise. While sea rise is slow & we could get out of the way in time to save our lives, once, say, Himalayan glaciers are all melted that will put an estimated 40% of China and India at severe risk of no water for irrigation, and consequent famine. And that story is repeated around the world where people depend on the annual cycle of glacier melt & replenishing to feed their rivers (& fishing industries) and irrigation canals. That’s the big story on the other side of the sea rise coin.

    We’ve got to keep looking at the big picture & the whole picture.

  22. 72
    Almuth Ernsting says:

    Re 70:
    If I’m understanding you correctly then you are saying that there is no evidence as yet to link worrying responses of plants, insects and animals to climate change, and that the peer-reviewed evidence is more about atmospheric warming, sea level rises and ocean acidification. Okay, I don’t know if there are studies yet about beetle infestations in Montana. But there are a lot of peer-reviewed studies into phenology, species extinctions, insect behaviour, etc. I understand that they are not discussed here because the people runnign this blog are climate scientists and not ecologists or biologists. This does not make those reports unscientific – it just means that we are yet to get a good weblog where climate scientists and biologists and ecologists work together. Meantime, the many peer-reviewed findings about the biosphere responding to climate change are no less scientific for this!

  23. 73
    pete best says:

    Re #70 I personally believe that as the atmosphere warms so there will be knock on effects to earths other sub systems including those studied by ecology and the like and that they are as scientific as other empirical sciences it is just that often what I read and believe to be possible in the more popular media even the more scientific media ends up being mistaken, wrongly reported or just plain misguided.

    This site has proved many things to me and cautions us all not to rush to conclusions just because a respected magazine or TV program says so.

  24. 74
    Ike Solem says:

    Regarding the applicability of these studies to future climate trends:

    Warmer than a Hot Tub: Atlantic Ocean Temperatures Much Higher in the Past

    This is the general reason why some people are saying that climate models which focus on the relatively recent geological past (ice age era) might be of limited use in predicting future climate trends. Not to say that these studies aren’t valuable in their own right in terms of benchmarking model performance.

  25. 75
    Hank Roberts says:

    Ike, who are the “some people” — what’s your source for the opinion stated about models?
    The press report you link to is about the recent Woods Hole study of marine sediments deposited when CO2 was over 1000 ppm. The article then talks about methane feedbacks. Current models don’t incorporate methane feedbacks, last I recall.

    The “some people” seem to be casting doubt on the models by asking the question asked long ago of Charles Babbage:

    “‘Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?’ I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.”
    http://www.hexatron.com/about/bab/index.html

  26. 76
    llewelly says:

    Changes in the timing of winter-spring streamflows in eastern North America, 1913-2002 . From the latest GRL. Related, but older, online material . Also related, but older, and about the western US .

    This snow-melt stuff isn’t really on topic for a thread about sea-level rise, but it does seem related to flooding, and to intensification of the hydrologic cycle, which keep coming here. Also, it’s more closely related to sea-level rise than black holes …

    Now, I have a question – does intensification of the hydrologic cycle play a role in glacier melting? If so, what role? (Ignore for the moment the relative paucity of glaciers in the aforementioned areas …)

  27. 77
    Stephen Berg says:

    Re: #74-75,

    “Some people” are weasel-words often used by those on FOX News and by climate skeptics. It tries to inject questions and disagreements where there really aren’t any.

    [Response:Allow me to interject with a couple of points of clarificatoin.
    1) The link in #74 about warm Atlantic temperatures is about a time millions of years ago, when carbon dioxide levels in Earth’s atmosphere were higher than present. That web site actually says "researchers say they may be an indication that greenhouse gases could heat the oceans in the future much more than currently anticipated. The study suggests that climate models underestimate future warming."
    2) I think it is fair to say that climate models which focus on the ice age might be of limited use in predicting future climate trends. In spite of the analogy made between the present and the Last Interglacial by the authors of the papers I've discusssed in this post, it is arguably a pretty weak analogy. The summertime insolation anomaly glacial-to-interglacial is something like 60 W/m2. That's why the glaciers melt! Even at 1000 ppm, CO2 doesn't provide that much forcing. --eric]

    [Response: I think the LGM is a somewhat better test for CO2 sensitivity than Eric implies, if used properly. To be sure, the summertime glacial to interglacial anomaly is 60 W/m**2, this is in the seasonal cycle, not the annual mean; the main response to this is in the NH, where the ice sheets are. The response to this seasonal anomaly is much attenuated in the tropics, and even more attenuated in the Southern Hemisphere. In the SH midlatitudes, the LGM cooling is mostly due to CO2 reduction amplified by cloud and water vapor and sea ice feedbacks -- plus a wildcard for what you think interhemispheric ocean heat fluxes are doing. In this regard, the SH cooling at LGM time provides a pretty pure example of the sensitivity of temperature to a reduction of CO2. The main assumption one then needs to make is that the sensitivity to an increase in CO2 from an interglacial base state is similar to the sensitivity to a reduction from the same state. The largely unexplained nature of the ice-free Cretaceous hothouse climates does suggest, however, that there may be some things going on at the warm end that aren't analogous to the glacial-interglacial transition. --raypierre]

    [Response: Well, the climate sensitivity estimate from the LGM data, discussed by Gavin in the previous post, is just out. As both the LGM climate and the CO2 doubling climate are simulated with the full model ensemble, this does not use the assumption that climate sensitivity is the same, going up to higher CO2 or down to lower CO2 levels. -stefan]

  28. 78
    Jason Burford says:

    Well i have read lots here, and it’s nice to get a consensus of some scientific thought

    Sorry for bursting in as a newbie, but

    It seems that we (being a climatologist myself, although young) are predominantly stuck in our pidgeon holes looking for variable a to explain b etc

    What of the other environmentalists…phenological studies…how can people accept our fears when they are stuck in one percepted area of science…why cant we do some correlations with more fields of study…how can we combat politicians with agendas of (dare i go there)or corporations bent on profit or even the guy on the street that is worried but sees NO instruments of change

    This may seem out of context but who give a fat lying pancake if sea level/temp rise x.y or x.z I mean really
    it’s all looking worse and I am, in my youth, surprised at the distraction/cowering tactics to face the problem/TRUTH…The young didn’t create this, but are now perpetuating

    No, I see a perpetuation of greed and feigned ignorance, especially in the US leadership, and now with Chindia….give me reason for hope

    With my few climate studies as a youth in here in Canada, I know there are always complaints about not enough intergration or communication(or data!)between scientists (e.g the man that looks at the river and the man that looks at the sky, even though they may be atop one another)

    IMVHO opinion to survive now (bird flu?)…Lets all get togethor in the name of humanity.

    Sorry if this is spam, but it cuts to the heart
    I don’t want to give up personally on humanity and hope the planet ‘gives us’ what we have from ignorance or laziness now apparently deserve.
    (we need Q to force a trial again)

  29. 79

    Re: 71

    One of those places “around the world” is most of the western US. Up here in Seattle, we have a reputation for lots of rain, but in fact, the summer here is usually bone dry for 3-4 months. Most of the water supply during those months comes from snow melt in the Cascades, but if the snow line rises and rain starts melting it earlier, that could cause big problems here.

  30. 80
    Hank Roberts says:

    Stefan (Response, bottom of #78) thanks for the link to Schneider et al. “just out”- it’s a PDF file.

    Brief snip:
    ” … a close link exists between the simulated warming due to a doubling of CO2, and the cooling obtained for the LGM. Our results agree with recent studies that annual mean data-constraints from present day climate prove to not rule out climate sensitivities above the widely assumed sensitivity range of 1.5-4.5C(Houghton et al. 2001). Based on our inferred close relationship between past and future temperature evolution, our study suggests that paleo-climatic data can help to reduce uncertainty in future climate projections.
    “Our inferred uncertainty range for climate sensitivity, constrained by paleo-data, is 1.2-4.3C and thus almost identical to the IPCC estimate.”
    [and add one degree C at the top, says their next paragraph]

  31. 81
    John Finn says:

    I’ve just been reading the above article when I noticed the following

    Finally, in a very nice bit of work Velicogna and Wahr use data from the “Gravity Recovery and Climate Experiment” (GRACE) satellites to show that the Antarctic ice sheet has been losing mass at a rate of 150 +/- 80 km3 each year since 2002.

    Is this correct? I mean the bit about “losing mass at a rate of 150 +/- 80 km3 each year since 2002″. Isn’t this rather a short period from which to be drawing any conclusions? Mind you I can see the advantages. No need to bother trawling through decades of data which can be a bit time-consuming. In fact, the more I think about it the more I like it – so much so I’ve even decided to do my own study.

    This study analyses land-based winter (Dec/Jan/Feb) temperatures in the Northern Hemisphere for the period 2001/02 to 2005/06. The data used in the study is from the GISS NH temperature record (that should keep everyone happy). OK …………….finished!

    Our results show that land-based NH winter temperatures have cooled by -0.028 deg C per year since 2001. If this trend continues NH winter temperatures will be -2.8 deg C (-5.0 deg F) below current levels within 100 years. The implications could be catastrophic. Snowfall levels in northern Europe may be up to lots more than they are at present.

    [that's dealt with the "could bes", "up tos", & "may bes" - now we need to finish with the heart-tugger for the media]

    Mammals which are native to the high northern latitudes may be forced to migrate in order to escape the harsher conditions. Some scientists believe Santa Claus may be forced to relocate as far south as Scotland. In a worst case scenario, Father Christmas may well be speaking with a glaswegian accent within 150 years.

    [Response: Maybe if you just kept reading:

    It is also important to remember that the data showing accelerating mass loss in Antarctica and rapid glacier flow in Greenland only reflect a very few years of measurements -- the GRACE satellite has only been in operation since 2002, so it provides only a snapshot of Antarctic mass changes. We don't really know whether these observations reflect the long term trend.

    - gavin]

  32. 82
    Stephen Berg says:

    “Unexpected warming in Antarctica”:

    “Winter air temperatures over Antarctica have risen by more than 2C in the last 30 years, a new study shows.

    Research published in the US journal Science says the warming is seen across the whole of the continent and much of the Southern Ocean.”

    http://news.bbc.co.uk/1/hi/sci/tech/4857832.stm

  33. 83
    Hank Roberts says:

    I recommend everyone look at what your local newspapers are printing about this subject in the past few days — this narrowly defined search found mine, sad to say:

    http://www.google.com/search?hs=Dj8&hl=en&q=%2B2006+%2B%22sea+level%22+%2B%2220+feet+by+2100%22&btnG=Search

    Write an editor — help stop the madness!

    [Response: Try clicking through. The original SF Gate article has actually been corrected and has had its title changed to '3 feet by 2100' (down from 20!). Most of the other hits are pick ups of the original (mistakenly headlined) article. There is some hope! - gavin]

  34. 84
    Paul says:

    ===Post #83
    [Response: Try clicking through. The original SF Gate article has actually been corrected and has had its title changed to '3 feet by 2100' (down from 20!). Most of the other hits are pick ups of the original (mistakenly headlined) article. There is some hope! - gavin]===

    Only the headline for the SF Gate article has been corrected. The actual article still states (four times)that there could be a 20 foot rise in sea level by 2100.

  35. 85
    Melvin Landers says:

    Why is the public so slow to respond to what is being reported concerning the rapidly changing climate? They are confused.

    Could the scientific community do anything to inspire public support for the needed changes? Yes.

    It is understandable that people are confused about changes in sea levels, melting ice and other results of global warming. For decades, the scientific community has used the phrases, â??present rate of changeâ?? and â??present rate of increaseâ?? when discussing continually changing projections. The rates are changing with every new discovery.

    The public is left believing that there are, in fact, great uncertainties in the conclusions and predictions of those in the scientific community. The great differences in recent reports on seal level changes bring this problem into better focus than other projections that seem to change over months or years of time. But, the variations in projected changes make skeptics of the people in the U.S.

    It is also understandable that modeled projections are based on presently observable rates. It would not be very scientific to base them on anything else. If the public is to be swayed, the reporting can not be left to environmental activists. They are not trusted by the people who need to make the greatest changes.

    There is now a critical need for an ambassador to assist the scientific community in its relations and communication with the rest of the world. The world needs to have a person with understanding of the science, a personable presentation and the respect of both the public and their peers. This person needs to present the uncertainties as what they are; the greatest reason of all to take action now.

    Then the scientific community needs to find a way to report its findings, based on present rates, but without giving the impression that they believe the rates will remain the same.

  36. 86

    Cilmate Change and the Media, Reality and the Future
    We are of course deeply heartened by the sudden clamor over climate change. 2006 may just be the year in which climate change will finally…

  37. 87

    Climate Change and the Media, Reality and the Future
    We are of course deeply heartened by the sudden clamor over climate change. 2006 may just be the year in which climate change will finally…


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