Not quite “we’re all going to die” again, but close. But this time by James Hansen, and published in Proceedings of the Royal Society.There is an the Indescribably-over-hypeded write up of it. Featuring:

nothing short of a planetary rescue will save it from the environmental cataclysm of dangerous climate change. Those are not the words of eco-warriors but the considered opinion of a group of eminent scientists writing in a peer-reviewed scientific journal.

Diversion: the article has a side bar pointing to Earth in peril: Climate change brings early spring in the Arctic which is a prime example of the sort of thing that really winds me up. Early spring: yes. Peril? Much less clear. After documenting various critters emerging early, it ends with “Dr Hoye warned that the change in timing of emergence, egg-laying and flowering could disturb local food webs with some animals appearing ahead or behind of others on which they rely for food.” Well its possible… but its not certain. Maybe they will just all have a nice long summer? Much of the “danger” estimates from climate change come from ecosystem responses, hopefully there are studies which actually show some likelihood of problems rather than just maybes.

Anyway, back to Hansen. It looks to be mostly a sea level rise paper. Hansen isn’t happy with the std IPCC estimates, because he thinks that Greenland and Antarctica will contribute more that the IPCC think. Why does he think this? Thats never been terribly clear to me; this is glacio stuff; he isn’t a glacio, and I don’t think many glacios agree with him. He says

The IPCC analyses and projections do not well account for the nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice shelves, nor are they consistent with the palaeoclimate evidence we have presented for the absence of discernible lag between ice sheet forcing and sea-level rise

and thats probably true for the first half: we don’t have a good understanding of that. Hansen seems to translate it into “and therefore they are going to fall apart quickly”. The new thing appears to be the palaeo evidence:

Their study looked back over more than 400,000 years of climate records from deep ice cores and found evidence to suggest that rapid climate change over a period of centuries, or even decades, have in the past occurred once the world began to heat up and ice sheets started melting

Hmm, not really sure what this is referring to. Maybe its necessary to actually read the paper. Well there is quite a lot of it. p1936 sez Sea level following Termination II may have reached 4+/-2 m higher than today (Overpeck et al. 2006), which would already qualify as dangerous change. OK, I’m happy with the idea that 4m of sea level change would be dangerous, if it occurred within a century. But will it… Global warming of approximately 3oC is predicted by practically all climate models for ‘business-as-usual’ (BAU) growth of GHGs (IPCC 2001, 2007). Yet IPCC (2001, 2007) foresees twenty-first century sea-level rise of only a fraction of a metre with BAU global warming. Their analysis assumes an inertia for ice sheets that, we argue, is incompatible with palaeoclimate data and inconsistent with observations of current ice sheet behaviour. This seems less reasonable: there is nothing in the palaeo data I can see that tells you sea level *will* rise within a century.

i-5a8b268059bdd8e2242ab14acbf1f72e-ar4_2090_t1.png Continuing, …As a result, large portions of West Antarctica and Greenland would be bathed in melt water. Already areas of summer melt have increased rapidly on Greenland (Steffen et al. 2004), the melt season is beginning earlier and lasting longer, and summer melt is being observed on parts of West Antarctica which doesn’t seem reasonable at all. Even in January most (or all, according to most of the GCMs I looked at) don’t have any areas above 0 oC by 2090-2100 over West Antarctica (assuming he doesn’t include the Peninsula in W Antarctica… most people don’t). My pic shows the fraction of AR4 models with sfc T above 0 oC in 2010-20 (left) and 2090-2100 (right), using a quick and dirty interpolation so there may be some dubious areas. So I think the models think there is precious little today and not much more by 2090 (incidentally GISS E, which was used in H06, seems to be one of the more enthusiastically warm over Antarctica).

OMiaC also doesn’t quite know what to make of Hansen.

Its very hard (from the paper) to work out what kind of probability Hansen thinks there is for large SLR within a century. But the paper ends with We have presented evidence (Hansen et al. 2006b) that the dangerous level of CO2 can be no more than approximately 450 ppm. Our present discussion, including the conclusion that slow feedbacks (ice, vegetation and GHG) can come into play on century time-scales or sooner, makes it probable that the dangerous level is even lower. OK, so the previous stuff says that 450 is “dangerous” (CO2 or CO2e?) and this stuff says that 450 is too high, “probably”. I don’t know about the previous papers, but if the present one is supposed to demonstrate that lower levels are dangerous then they become irrelevant. But I don’t think that the present one *does* establish that 450 or lower is “probably dangerous”.

There is more inconclusive discussion on the Global Change group.


  1. #1 fergus

    The whole argument seems to rest on one huge conditional: if non-linear, wet process, warming-induced change is stimulated by a warming within the parameters suggested for a BAU, or 450ppm (CO2, not CO2e) scenario, then the WAIS might collapse suddenly. And this is conditional on the assumption that the WAIS glaciers will be undercut by seawater influx over the ‘ridges’ which hold back the flow. It’s one thing to claim this is possible, another entirely to imply that it is likely or ‘imminent’.

    OTOH, there’s a new paper on Greenland out today in GRL, which points to topographically-induced enhancement of sub-glacial warming, which might go some way to helping us understand the processes involved in glacier acceleration.

    Whilst I applaud Hansen’s intention (get them scared), what this seems to be is a rehash of the ‘dangerous climate change’ paper, with emphasis placed on ice sheets; what’s new in it? Not a lot that I can see.

  2. #2 Alexander Ac

    Dear William,

    I have several points – first, here are the words of leading expert on Greenland, Jay Zwally –

    “We are seeing things taking place in the ice now that weren’t expected, that five years ago we didn’t even know about,” said Zwally, who will spend his 14th summer on the Greenland ice cap this year.

    then you are probable aware of icequakes in Greenland- -this is what Hansen probably had in mind by non-linear response. Further, melted ice has lower albebo, than fresh ice…

    All glaciologists have been surprised by the collapse of Larsen ice sheet –
    we also should not forget, that a lot of new evidence for *possible* fast melting was obtained after 2005.

    It would be nice to know, what Zwally thinks about “Earth in imminent peril”… though I guess it will not be much different from Hansen…

    and finally, Ken Caldeira said: “History of climate modelling is a history of underestimating the effects of global warming”

    [I disagree with much of that. JZ is a fine scientist, but there is no need to puff him up. And his quote... well, what does it mean? Melting snow has a lower albedo, but as I pointed out, W Ant is unlikely to get above freezing. And no, the collapse of the Larsen wasn't desperately surprising - in fact Chris Doake predicted it. And what evidence does KC provide for his quote? -W]

  3. #4 Luboš Motl

    Hansen is like a kid who interpolates 11 points in a plane by a polynomial of 10th degree, then extrapolates the polynomial away from the original interval, and comes close to a heart attack when he sees that the graph grows like a tenth power for large values of “x”. There is no meaningful argument in his paper that would support the thesis that there are mostly positive feedbacks. There is no meaningful argument that would indicate that the models they think about with a chaotic interplay of dozens of randomly chosen effects are correct models. It is a work of pure hysteria. Click my name to learn more.

    At any rate, Hansen has figured out that consensus was only good to achieve the first cosmic speed of hysteria. Now this, consensus part of the rocket must be thrown away to achieve the second cosmic speed of hysteria. When others disagree with IPCC, they’re heretics. However, Hansen is a prophet who is gonna make the second cosmic hysterical speed, so newspapers support him.

  4. #5 Luboš Motl

    Klaus has answered 18 questions of the Financial Times readers, see

  5. #6 Alexander Ac

    Lubos, as you show in your blog (China is surpassing USA in CO2 emissions) – neither 1st nor 2nd cosmic speed is enough to significantly slow down CO2 increase… :-)
    maybe hysteria is one thing, and to do *something* is quite different

  6. #7 Luboš Motl

    I completely agree with you, Alexander. Hysteria has nothing to do with doing useful things. Unless you wanted to say that one needs a 3rd cosmic speed of hysteria and then it will work. ;-)

  7. #8 Luna_the_cat

    Uh, yeah, no bias there, Lubos, just a dispassionate analysis of the facts. In the same vein, I’m also really King Louis XIV of France.


    Is Hansen too hysterical? Yeah. Is he wrong? Possibly. There are legitimate reasons to think the Greenland and land-bound Antarctic glaciers are more unstable than expected; the fact they’re already moving far faster than people thought already is one reason, and a few plausible types of instability which are being detected now are more. However, there are many other possible confounding factors.

    It’s pretty certain we will see sea level change, and I think the lower limit on how much over the next century has been plausibly set at 20cm. And we know that sea level can change quite quickly, viz. the end of the Younger Dryas — but we don’t yet know if we’re looking at anything like that now. Another decade, we’ll know lots more.

    I don’t personally blame a lot of the client scientists for becoming increasingly frantic. They see a problem, they’re convinced it’s a big problem, and they can’t get people to move on it — in fact, there’s still a large population who refuse to believe there’s any problem at all (take a bow, Lubos!). Problem is, if they don’t use strong language, the point totally misses some people, and if their language is too strong they alienate more people. Difficult line for them to walk.

  8. #9 Brian Schmidt

    “hopefully there are studies which actually show some likelihood of problems rather than just maybes.”

    I saw a study a while back showing an important insect species hatched based on climate, while its predator bird nested on a genetic calendar. I’ll see if I can find it.

    Replacing tundra with forest is also likely to result in more than a long summer for tundra species.

    I haven’t seen any discussion of this, but I expect the decrease and thinning of permafrost will significantly decrease wetlands. That would have a dramatic impact on arctic systems and migrating waterfowl.

  9. #10 Alexander Ac

    I really don’t know, what the “mainstream” glaciologists say… so for know, let’s hope IPCC got it right.

    I also don’t know, whats the support for KC statement, I am not able to find that article…

    anyway, the question is, if papers like that of Hansen are *helping* the CO2 reduction or not. But with great confidence we can say, that the truth is somewhere between Hansen and Lubos :-)

  10. #11 Eli Rabett

    While Hansen is not a glaciologist, he has been working on sea level rise issues for over 25 years so he certainly is familiar with work on glaciers and ice caps.

    One of the things to bear in mind with ice is that there IS a tipping point. Not damn much is going to happen as long as the temperature remains below freezing every damn day of the year, but. . .

    [I'm not sure that is true. In fact there is no real evidence for this "tipping point" stuff at all (see

    And even if there was one, for a particular location, it isn't clear that there would be for the whole sheet given spatial variation.

    Hansen may be right - who knows. But at the moment, I think he is hand waving -W]

  11. #12 Luboš Motl

    Dear Luna the Cat,

    you got many adjectives and other things upside down. You said that there are still people who say that there is no AGW problem. Quite on the contrary. There are people who already know that AGW is not a problem.

    IPCC didn’t set the lower limit on 20 cm but 14 cm, if you kindly look, and your very choice of talking about “lower limits” shows your bias. No upper limit and no lower limit on such estimates is 100% guaranteed. But even 1 meter per century would be completely unspectacular from the humanity’s viewpoint.

    Your comment that the message of catastrophe misses the public shows that you must live in a different Universe. People are bombed by 30,000+ newspaper articles a month – and I only count those collected by – and all of them contain increasingly hysterical descriptions of a problem that clearly doesn’t exist.

    If you support the hysterization, what exactly do you want to achieve, a 100% consensus of the citizens? Do you want normal people to behave as naked biking environmentalists? I assure you that you won’t achieve any consensus by screaming loudly. With the evidence missing just like today, millions of intelligent people will keep on thinking the same thing as we do today – that ecoscreamers are not sane. The more you scream nonsense, the more nuts you are. There are other millions who are easily manipulable by screaming – but you have already gotten pretty much all of them. So why do you keep on screaming?


  12. #13 Eli Rabett

    Actually Luby, we are laughing our butts off at your act.

  13. #14 guthrie

    Lubos- where is your evidence for the assertion that even 1 metre sea level rise per century would be completely unspectacular?
    If by spectacular you mean similar to the effect blowing up a levee would have, then of course it will not. But in terms of infrastructure damage, movement of people and places etc, it would be rather spectacular.

  14. #15 Luboš Motl

    People like you have no idea about the real world and they don’t care. It’s enough if they spread their stupidity to others.

    First of all, the “upper bound” by IPCC is 43 centimeters. But as I said, even 1 meter in 100 years would be unspectacular. What do I mean?

    [There is no upper bound from IPCC. There are only various estimates. If you insist on taking the highest of these, its 0.59 -W]

    For example, this region of the Netherlands

    is situated seven meters below the sea level. And what? It also took roughly a century or two to get to this level, and they had worse technologies. So I think that 7 meters per century would be a detectable problem that would give some jobs and required some efforts, but it would surely be extremely far from a catastrophe.

    1 meter in 100 years is ludicrous. I mean, this is still comparable to the normal movements that the sea level has always been doing. Sometime in the past, it was faster. We’re not talking about any deaths here. One has 100 years to walk away. What are you talking about? I think that it makes no sense to talk to people who are not able to answer this question – whether 1 meter in 100 years is a disaster – themselves.

    There exists no calculation and no number that would indicate that the climate will cause some global tragedies in the next 100 years. The more someone says something else, the more lies he or she spreads.

    [I disagree with both you and Hansen. 1m is certainly possible - unlikely, perhaps, but possible (of course if you don't believe that T is going to go up then its implausible - I'm assuming for the purposes of this that we're talking about what might happen to SL *if* T went up 3 oC, say). Its clear that we don't have really good models of the ice sheet response to T change. Given our ignorance, saying that 1m is "ludicrous" is totally unscientific - we simply don't know -W]

  15. #16 maksimovich

    Hansen forgot to observe what Gaia was doing though,forgetting that change is opportunity,in a mixed biological “market’–aih061907.php

  16. #17 Eli Rabett

    In Gaia vision, change is usually an opportunity for your species to become food or compost

  17. #18 Eli Rabett

    The US East Coast barrier islands (Key West to Cape Cod)are toast at 1m. The investment in buildings/land is trillions of dollars. A strong hurricane or Northeaster on top of high tide and a 1 m rise will make NO look like a tea party. I suggest that string theory is not the best base for confronting reality.

  18. #19 guthrie

    I love how Lubos avoids actually making concrete statements.

    From my own personal knowledge, a 1 metre sea level rise in a century would put 3 golf courses at St Andrews under complete risk of erosion, necessitating expensive dykes an dams and stuff.

    Then take London. ACcording to this web page,

    1. According to present Government estimates, a flood would cost around £30 billion, around 2% of the UK’s GDP (Jane Kettle, EDIE 1/4/2005). By comparison, the cost of the barrier is estimated to have been around £1.3 billion pounds in current money.”

    The current Thames barrier has a life up to 2030, supposedly. Building barriers capable of going on well past 2100 and coping with a metre and more of sea level rise will cost many billions of pounds. If the sea level rise occurs, and the defences cannot cope, thats £30 billion down the drain, and probably more- look how much it is costing for New Orleans.

    I hardly think either of these probabilities are unspectaular. When multiplied out across the globe, the dangers are gigantic.

  19. #20 jay alt

    The costs of dealing with a 1 meter rise in sea level make the Iraq war look like a bargain.

    [Interesting maps, but thats 1.5m at the lowest, and I don't see any cost estimates -W]

  20. #21 Pau

    The AR4 models for yr 2100 probably assume no surface lowering in the continental interiors, which wouldn’t be true if ice was streaming toward the oceans because of ice shelf collapse due to warming ocean temps. Summer surface melt would eventually play a role in crevasse propagation and interface lubrication near sea level. Hasn’t anyone looked at what kind of ice flux increase would be needed to deflate significantly the ice surface in a few basins in West Antarctica?

    [The Hadley Centre have run an ice model coupled to Greenland - thye use this because sfc T's warm as the ice lowers. But the results are not dramatic. They don't contain any terms for exciting lubrication though -W]

  21. #22 Pau

    If I undestand well, Hadley Center people modeled the Greenland ice sheet but Greenland’s bottom is above sea level and has significant relief. Ice streaming couldn’t happen there the way it’s likely to happen in w.Antarctica where the classic thinning-buoyancy-speedup feedback of retreating maritme glaciers would play a significant role in bringing over time a large part of the ice surface in these basins close to sea level.

    [Maybe, but Greenland is more likely to get warm enough to melt to start the cycle -W]

  22. #23 Pau

    Even with Greenland getting warm first, it isn’t as likely to see a very rapid surface drawdown like W Antarctica could see if the ice shelves collapsed so the cycle isn’t comparable. Greenland would probably melt in the better part to the small multiple of a 1000 yr even with lubrication of the basal contact. We just don’t know the relevant time scale for W Antarctica but we know that maritime glaciers retreat extremely quickly once they aren’t pinned at the grounding line.

    [We do? Which maritime glaciers? -W]

  23. #24 Pau

    I don’t think there is much of a doubt that maritime and lacustrine glaciers can retreat very quickly and are often out of sink with climate especially on shorter time scales (decades) because relative sea level can exert a much stronger control on terminus position than surface mass balance.

    It’s also true that we know mostly of subpolar glacial systems of small to medium size (esp. post-LIA in Alaska, Patagonia, ..) that retreated very quickly but Ant. Peninsula and some Greenland glaciers are presently showing that fast retreat rates are possible in colder environments. Environments not as cold as WAntarctica, but ocean temps seem to be most critical to grounding line stability with great effect on the glaciers of the Amundsen Sea area. Surface temps and melt events are not important in WAntarctica today but these systems aren’t frozen to their beds for quite a ways upstream and have active subglacial hydrology so no surface melt is needed there to lubricate the basal contact and start deflating the ice sheet.

  24. #25 Hank Roberts

    Loose ends — in the first post you write, quoting

    ” and summer melt is being observed on parts of West Antarctica” and then comment:
    which doesn’t seem reasonable at all.

    I didn’t find a cite, but — this perhaps?

    ——–begin quote ————
    “The January 2005 discovery is the first widespread Antarctic melting detected with NASA’s QuikScat satellite and the most significant melt observed using satellites in 30 years. The affected regions encompass a combined area as big as California.

    Son Nghiem of the National Aeronautics and Space Administration’s Jet Propulsion Laboratory and Konrad Steffen, director of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado-Boulder, led the team.

    They said the melting occurred in multiple distinct regions, including far inland, at high latitudes and at high elevations — all areas where melt had been considered unlikely. The scientists determined maximum air temperatures at the time of the melting exceeded 41degrees Fahrenheit in one of the affected areas and remained above freezing for approximately a week…..”
    ——- end quote——-