In an earlier post, we discussed a review article by Frohlich et al. on solar activity and its relationship with our climate. We thought that paper was quite sound. This September saw a new article in the Geophysical Research Letters with the title «Phenomenological solar signature in 400 years of reconstructed Northern Hemisphere temperature record» by Scafetta & West (henceforth referred to as SW). This article has now been cited by US Senator James Inhofe in a senate hearing that took place on 25 September 2006 . SW find that solar forcing accounts for ~50% of 20C warming, but this conclusion relies on some rather primitive correlations and is sensitive to assumptions (see recent post by Gavin on attribution). We said before that peer review is a necessary but not sufficient condition. So what wrong with it…?
Climate Science
Con Allègre, ma non troppo
Guest Commentary by Georg Hoffmann (LSCE)
Climate change denial is not necessarily a speciality of Washington DC think tanks – sometimes it can also be found in old Europe. Right now there is a little media storm passing by in France evoked by an article from Claude Allègre in L’Express. Who is Claude Allègre? He is one of the most decorated french geophysicists specializing in geochemistry and the use of paleomagnetism. Being a longtime friend of the former prime minister, Lionel Jospin, he even became Minister of Education and Research in the former Socialist government. He still plays an active role within the Socialist party and though he has never published anything directly related to anthropogenic climate change, one would assume that he has some understanding of the scientific matter. But this assumption would be wrong.
In the French weekly journal l’Express he exposed his “sceptical” views in an article entitled “The snows of Kilimanjaro”. In the short editorial, he somehow became lost when following Ernest Hemingway to East Africa. Allègre mentions two scientific examples to demonstrate that there is something fundamentally wrong in the IPCC statements on the reality of climate change. First, he commented on the disappearing glaciers of the Kilimanjaro, sometimes treated as the “Panda” of anthropogenic climate change. Citing a “Nature” study (which was in fact published in Science) by Pierre Sepulchre and colleagues from my laboratory, he claimed that this modelling study demonstrated that Kilimanjaro’s glaciers are controlled by tectonic activity. In fact, the article describes the impact of tectonics of the East African Highlands on Indian ocean moisture transport —- on a time scale of millions of years! This confuses glacier variability over the last ~100 years with rainfall trends extending back to the time of the early hominids (such as Lucy).
In fact, there are good reasons to believe that the situation on the Kilimanjaro is a bit more complicated than a simple “atmosphere gets warmer/ glaciers are melting” equation (for instance, see this previous post on tropical glacier retreat). Furthermore, the real link to climate change does not come from the retreat of one single tropical glacier, but from the fact that, to my knowledge, all studied tropical glaciers have retreated over the 20th century, and the retreat rates have generally increased in recent decades.
Allègre’s misunderstanding was immediately followed by another one. Citing a recent study on relatively stable Antarctic snowfall over the last 30 years (Monaghan et al, 2006, discussed here) , he highlighted what he thought was a clear contradiction to future climate simulations of global circulation models (melting of the Antarctic ice sheet). However, that’s not what they predict. All models predict a comparably stable Antarctic ice sheet for the 21th century in which comparably moderate temperature changes in Antarctica are compensated by slight increase in snowfall. The Monaghan et al study does not contradict these model scenarios.
The French climate research community was of course not very pleased about this short sequence of misrepresentations and personal attacks (“les Cassandres”) and corrected Allègre in an open letter published here on the website of the Institute Pierre Simon Laplace (which includes links to the ongoing back and forth, for those that speak French).
Curiously enough, twenty years ago Allègre wrote in “Clés pour la géologie”, (éd. Belin/France Culture):
“En brûlant des combustibles fossiles, l’homme a augmenté le taux de gaz carbonique dans l’atmosphère, ce qui fait, par exemple, que depuis un siècle la température moyenne du globe a augmenté d’un demi-degré.”
(Translation)
“By burning fossil fuels man enhanced the concentration of carbon dioxide in the atmosphere which has raised the global mean temperature by half a degree in the last century”.
But at that time he used this argument against the anti-nuclear energy movement. It might be that there is simply a bit too much politics in Allègre’s life…
Attribution of 20th Century climate change to CO2
) The discussion of climate change in public (on blogs, in op-eds etc.) is often completely at odds to the discussion in the scientific community (in papers, at conferences, workshops etc.). In public discussions there is often an emphasis on seemingly simple questions (e.g. the percentage of the current greenhouse effect associated with water vapour) that, at first sight, appear to have profound importance to the question of human effects on climate change. In the scientific community however, discussions about these ‘simple’ questions are often not, and have subtleties that rarely get publicly addressed.
One such question is the percentage of 20th Century warming that can be attributed to CO2 increases. This appears straightforward, but it might be rather surprising to readers that this has neither an obvious definition, nor a precise answer. I will therefore try to explain why.
[Read more…] about Attribution of 20th Century climate change to CO2
Carl Wunsch, The Economist and the Gulf Stream
Carl Wunsch usually has very interesting things to say about the climate system, and although his arguments don’t necessarily win everyone completely over, they often generate an improvement in the level of scientific discussion. In this week’s Economist, he has a letter printed concerning the mis-definition of the ‘Gulf Stream’ concept in the magazine’s climate change survey a couple of weeks ago. This is essentially a reprint of his letter to Nature that was published in 2004, which stated correctly that the Gulf Stream is basically a wind driven phenomenon and will not stop or reverse while the wind still blows and the Earth still turns. [Read more…] about Carl Wunsch, The Economist and the Gulf Stream
Sachs’ WSJ Challenge
Jeffery Sachs of the Columbia Earth Institute has an excellent commentary in Scientific American this month on the disconnect between the Wall Street Journal editorial board and their own reporters (and the rest of the world) when it comes to climate change. He challenges them to truly follow their interest in an “open-minded search for scientific knowledge” by meeting with the “world’s leading climate scientists and to include in that meeting any climate-skeptic scientists that that the Journal editorial board would like to invite”.
RealClimate heartily endorses such an approach and, while we leave it to others to judge who the ‘world leading’ authorities are, we’d certaintly be willing to chip in if asked. To those who would decry this as a waste of time, we would point to The Economist who recently produced a very sensible special on global warming and proposed a number of economically viable ways to tackle it, despite having been reflexively denialist not that many years ago. If the Economist can rise to the challenge, maybe there is hope for the Wall Street Journal….
The trouble with sunspots
by Gavin Schmidt and Michael Mann
Solar forcing of climate is a subject that gets far more attention than any new observations or improved understanding would warrant. Two new articles appearing today attest to that. One is occasionally tempted to agree with Oscar Wilde when he said:
Why does not science, instead of troubling itself about sunspots, which nobody ever saw, or, if they did, ought not to speak about; why does not science busy itself with drainage and sanitary engineering?
Except in this case it’s Nature rather than Science who are troubling themselves…
A new review paper by Foukal et al does a reasonable job summarising the mainstream opinion on the issue. In particular, they outline quite clearly why some ideas related to long term solar variability (such as solar disk radius changes, or the difference between cycling and non-cycling stars) have recently fallen out of favor. Indeed, they assert that there is little evidence for any solar variability in irradiance that is not related to the shielding/enhancements of sunspots and faculae – which implies only a modest decrease in solar flux at the Maunder Minimum for instance. We could quibble with their use of paleo-reconstructions, their climate modeling approach, and the rather cursory treatment of the substantial body of work relating to amplyfying mechanisms due to UV/ozone links, but we’ve gone over this ground before and we refer readers to those earlier discussions.
Slightly more novel is the description in the News section of a new experiment at CERN that is attempting to test the cosmic-ray/cloud hypothesis by building a large cloud chamber mimicing the atmosphere and firing high energy particles at it. There’s nothing intrinsically wrong with the idea, but given the $11 million to spend on climate change research, we would have tended to favour projects that, unlike this one, have at least some empirical support within the observations….
Weekly Round-up
A few scattered pieces that may be of interest:
The increasingly-odd behaviour of the American Association of Petroleum Geologists – who recently awarded Michael Crichton a journalism award (because his work apparently has the ‘ring of truth‘ as opposed to actually being true), aroused the ire of American Quaternary Association in a commentary in EOS.
Reason Magazine has a Roundtable discussing responses to global warming from their particular perspective. The second essay (by D. Boudreaux) has the remarkable subtitle “Why ignoring climate change isn’t a sign of scientific illiteracy or of ideologically induced stupidity”. His point appears to be that the science of climate change doesn’t specifically imply any particular actions in response (which is true – what action to take, if any, is a political, ethical and economic decision). However his conclusion that ignoring climate change is sensible postition to take is indeed pretty dim. Ignorance is never the answer.
And on a lighter note, the Union of Concerned Scientists has a cartoon competition.
Tropical SSTs: Natural variations or Global warming?
by Michael Mann and Gavin Schmidt
Roughly a year ago, we summarized the state of play in the ongoing scientific debate over the role of anthropogenic climate change in the observed trends in hurricane activity. This debate (as carefully outlined by Curry et al recently) revolves around a number of elements – whether the hurricane (or tropical cyclone) data show any significant variations, what those variations are linked to, and whether our understanding of the physics of tropical storms is sufficient to explain those links.
Several recent studies such as Emanuel (2005 — previously discussed here) and Hoyos et al (2006 — previously discussed here) have emphasized the role of increasing tropical sea surface temperatures (SSTs) on recent increases in hurricane intensities, both globally and for the Atlantic. The publication this week of a comprehensive paper by Santer et al provides an opportunity to assess the key middle question – to what can we attribute the relevant changes in tropical SSTs? And in particular, what can we say about Atlantic SSTs where we have the best data? [Read more…] about Tropical SSTs: Natural variations or Global warming?
Why greenhouse gases heat the ocean
Guest commentary by Peter Minnett (RSMAS)
Observations of ocean temperatures have revealed that the ocean heat content has been increasing significantly over recent decades (Willis et al, 2004; Levitus et al, 2005; Lyman et al, 2006). This is something that has been predicted by climate models (and confirmed notably by Hansen et al, 2005), and has therefore been described as a ‘smoking gun’ for human-caused greenhouse gases.
However, some have insisted that there is a paradox here – how can a forcing driven by longwave absorption and emission impact the ocean below since the infrared radiation does not penetrate more than a few micrometers into the ocean? Resolution of this conundrum is to be found in the recognition that the skin layer temperature gradient not only exists as a result of the ocean-atmosphere temperature difference, but also helps to control the ocean-atmosphere heat flux. (The ‘skin layer‘ is the very thin – up to 1 mm – layer at the top of ocean that is in direct contact with the atmosphere). Reducing the size of the temperature gradient through the skin layer reduces the flux. Thus, if the absorption of the infrared emission from atmospheric greenhouse gases reduces the gradient through the skin layer, the flow of heat from the ocean beneath will be reduced, leaving more of the heat introduced into the bulk of the upper oceanic layer by the absorption of sunlight to remain there to increase water temperature. Experimental evidence for this mechanism can be seen in at-sea measurements of the ocean skin and bulk temperatures. [Read more…] about Why greenhouse gases heat the ocean
Chinese whispers in Australia
We decided months ago that we would not comment on leaks of the draft of the upcoming IPCC report (due Feb 2007) but we are prepared to correct obvious errors. The ongoing revisions of the text and the numerous drafts make any such commentary, let alone conclusions drawn from it, pretty pointless. This is even more true when the leaks are obviously confused about a central point. The principle error in the latest ‘exclusive’ is that the writer confuses a tightening of the estimate of climate sensitivity to 2xCO2 (as discussed here) with projections of climate change in 2100. These projections obviously depend on the uncertainties in the scenarios of future technology, economic progress and population (etc.) plus uncertainties in feedbacks related to the carbon or methane cycles. Unfortunately these have not been reduced since the last assessment report (and in some cases have actually increased).
That occasional stories will come out that get basic things wrong is unfortunate but not surprising. What is more troubling is that they subsequently get picked up by Reuters and UPI, and republished in places (such as Scientific American, though in their defence, it is simply a posting of the wire report) where the editors should know better. Worse still, the wire service stories are too brief to make the source of the error obvious, and thus the error gets propagated in an ever more confused state. As usual the blogsphere is playing a key role in amplifying and further muddying the story. The advantage of blogs is that errors can be corrected quickly, and the comments on Prometheus for instance, quickly revealed the confusion and the potential agenda of the original story.
There will be plenty of time to discuss the new IPCC report when it comes out and where everyone can read for themselves what has and what hasn’t changed since 2001. Until then, we would counsel against journalists and editors jumping at supposed ‘exclusives’ and – more dangerously – going ahead with them without even a basic sanity check of the details.