RealClimate

Climate science from climate scientists...

You are here: Home / Archives for Climate Science

Climate Science

What links the retreat of Jakobshavn Isbrae, Wilkins Ice Shelf and the Petermann Glacier?

by

Guest commentary from Mauri Pelto

Changes occurring in marine terminating outlet glaciers of the Greenland Ice Sheet and ice shelves fringing the Antarctic Peninsula have altered our sense of the possible rate of response of large ice sheet-ice shelf systems. There is a shared mechanism at work that has emerged from the detailed observations of a number of researchers, that is the key to the onset and progression of the ice retreat. This mechanism is shared despite the vastly different nature of the environments of Jakobshavns Isbrae, Wilkins Ice Shelf and the Petermann Glacier.
[Read more…] about What links the retreat of Jakobshavn Isbrae, Wilkins Ice Shelf and the Petermann Glacier?

Palin on Global Warming

by

Translations: (Italian) (English)

Here at RealClimate we understandably have an intense interest in the positions of the Presidential and Vice-Presidential candidates regarding global warming and carbon emissions. What the stance bodes for future action on climate change is consequential in itself, but beyond that the ability to use sound science in this case serves as a bellweather for the candidates’ whole approach to science. Whatever else you can say about the candidates, it has been encouraging that both John McCain and Barack Obama favor mandatory action to reduce US carbon emissions.

But, enter Gov. Sarah Palin, McCain’s pick for VP. Palin’s position on global warming has been stated quite clearly in this recent interview with the publication Newsmax , where she says “A changing environment will affect Alaska more than any other state, because of our location. I’m not one though who would attribute it to being man-made.” How is this to be reconciled with McCain’s position? Do they just agree to differ? What does this bode for future actions if McCain were to win the election, especially in view of the fact that, in a Cheney-esque way, Palin is likely to be put in charge of energy policy? The recent vice-presidential debate sheds some light on the issue. A full transcript of the debate is here.

[Read more…] about Palin on Global Warming

A new survey of scientists

by

Translations: (Deutsch) (English)

Dennis Bray and Hans von Storch have been making surveys of climate scientists for a number of years with the reasonable aim of seeing what the community thinks (about IPCC, climate change, attribution etc). They have unfortunately not always been as successful as one might like – problems have ranged from deciding who is qualified to respond; questions that were not specific enough or that could be interpreted in very different ways; to losing control of who answered the questionnaire (one time the password and website were broadcast on a mailing list of climate ‘sceptics’). These problems have meant that the results were less useful than they could have been and in fact have occasionally been used to spread disinformation. How these surveys are used obviously plays into how willing scientists are to participate, since if your answers are misinterpreted once, you will be less keen next time. Others have attempted similar surveys, with similar problems.

As people should know, designing truly objective surveys is very tricky. However, if you are after a specific response, it’s easy to craft questions that will favour your initial bias. We discussed an egregious example of that from Steven Milloy a while ago. A bigger problem is not overt bias, but more subtle kinds – such as assuming that respondents have exactly the same background as the questioners and know exactly what you are talking about, or simply using questions that don’t actually tell you want you really want to know. There are guides available to help in crafting such surveys which outline many of the inadvertent pitfalls.

Well, Bray and von Storch have sent out a new survey.

[Read more…] about A new survey of scientists

On straw men and Greenland: Tad Pfeffer Responds

by


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.

Simple Question, Simple Answer… Not

by

Translations: (Français) (Japanese) (Finnish) (Czech) (English)

Guest commentary by Spencer R. Weart, American Institute of Physics

I often get emails from scientifically trained people who are looking for a straightforward calculation of the global warming that greenhouse gas emissions will bring. What are the physics equations and data on gases that predict just how far the temperature will rise? A natural question, when public expositions of the greenhouse effect usually present it as a matter of elementary physics. These people, typically senior engineers, get suspicious when experts seem to evade their question. Some try to work out the answer themselves (Lord Monckton for example) and complain that the experts dismiss their beautiful logic.

The engineers’ demand that the case for dangerous global warming be proved with a page or so of equations does sound reasonable, and it has a long history. The history reveals how the nature of the climate system inevitably betrays a lover of simple answers.

[Read more…] about Simple Question, Simple Answer… Not

Friday round-up

by

Blogging has been a little light recently (apologies!), but here are a few pieces that have caught our eye this week.

First up, the Columbia Journalism Review has a two–parter on journalistic coverage of climate change inspired by comments from Jeff Huggins on the Andy Revkin’s Dot Earth blog. The key issues CJR addresses are familiar ones to readers here: how to communicate mainstream science in a way that doesn’t distort the reality of the consensus on many issues in favour of controversy on more cutting-edge topics. Definitely worth a read, and proof (if such were needed) that commenting on blogs can make a difference to coverage.

Next, the role of CO2 as a long-term climate forcing. The old CO2 lead/lag issue keeps making the rounds as a contrarian talking point (and made a brief resurgence here in comments this week) despite the fact that the existence of impact of climate on the carbon cycle in no way invalidates the impact of CO2 (as a greenhouse gas) on climate. However, there is a nice paper in Nature this week (Lunt et al, 2008) which looks at the various proposed triggers for the onset of the quaternary glaciations at the end of the Pliocene (~3 million years ago). These triggers involve, permanent El Nino events, the closing of the Isthmus of Panama, changes in orbital forcing, tectonic uplift of the Rocky mountains – and long-term decreases in CO2 as a function of very slow variations in sea floor spreading and chemical weathering. Lunt et al find that only the change in CO2 (400 ppm to 280 ppm) can explain the changes in the ice sheet. None of the other ideas come even close.

Thus, it looks very much like the climate changed radically due to this externally forced drift in CO2 (and tectonic is external for climate purposes on this timescale). As a corollary, this is an expansion of the idea we discussed a few months back, that the long term changes in the Earth system due to external forcings might be well be larger than the classical (Charney) sensitivity we often talk about.

Third. There has been a lot of discussion on energy futures in the comments – Nature had a good rundown of the scientific constraints on the different prospects. But this video is a quite entertaining discussion of why we just can’t get our heads around the issue from Dan Gilbert (h/t GH).

Finally, a commentary on the prospects for continued employment as an Arctic ice expert (h/t Climate Feedback).