Climate Science

This article continues the critique of writings on climate change by Allègre and Courtillot, started in Part I . If you would like to read either post in French, please click on the flag icon beside the post title above.

Prelude: It’s the physics, stupid

…which of course is a paraphrase of Bill Clinton’s famous quote regarding the economy. We put the last word in small letters since we’ve learned that it is not a good debating technique to imply (even inadvertently) that those who are having trouble seeing the force of our arguments might be stupid. What we wish to emphasize by this paraphrase is the simple fact that the expectation of a causal link between increasing long-lived greenhouse gases (like CO2) and increasing temperature does not rest on some vague, unexplained correlation between 20th century temperature and 20th century greenhouse gas concentration.

The anticipated increase in temperature was predicted long before it was detectable in the atmosphere, indeed long before it was known that atmospheric CO2 really was increasing; it was first predicted by Arrhenius in 1896 using extremely simple radiation balance ideas, and was reproduced using modern radiation physics by Manabe and co-workers in the 1960’s. Neither of these predictions rests on general circulation models, which came in during subsequent decades and made more detailed forecasts possible.

Still, the basic prediction of warming is founded on very fundamental physical principles relating to infrared absorption by greenhouse gases, theory of blackbody radiation, and atmospheric moist thermodynamics. All these individual elements have been verified to high accuracy in laboratory experiments and field observations. For a time, there was some remaining uncertainty about whether water vapor feedback would amplify warming in the way hypothesized in the early energy balance models, but a decade or two of additional observational and theoretical work has shown that there is no real reason to doubt the way in which general circulation models calculate the feedback. When modified by inclusion of the cooling effect of anthropogenic aerosols, the theory gives a satisfactory account of the pattern of 20th and 21st century temperature change.

No other theory based on quantified physical principles has been able to do the same. If somebody comes along and has the bright idea that, say, global warming is caused by phlogiston raining down from the Moon, that does not make everything we know about thermodynamics, infrared absorption, energy balance, and temperature suddenly go away. Rather, it is the job of the phlogiston advocate to quantify the effects of phlogiston on energy balance, and incorporate them in a consistent way beside the existing climate forcings. Virtually all of the attempts to poke holes in the anthropogenic greenhouse theory lose sight of this simple and unassailable principle.

In a paper entitled "Are there connections between the Earth’s magnetic field and climate?" published recently in Earth and Planetary Science Letters, Courtillot and co-authors attempt to cast doubt on carbon dioxide as a primary driver of recent (and presumably future) climate change; he argues instead that fluctuations in the Earth’s magnetic field (partly driven by solar variability) have an important and neglected role. Like most work of this genre, it is carried out in an intellectual void — as if everything we know currently about physics of climate had to be set aside in order to make way for one new (or in fact not-so-new) idea. But the problems don’t end there. With the help of a Comment published by Bard and Delaygue (available here at EPSL or here as pdf) , we’ll expose a pattern of suspicious errors and omissions that pervades Courtillot’s paper. Sloppiness and ignorance is by far the most charitable interpretation that can be placed on this pattern.

[Read more…] about Les Chevaliers de l’Ordre de la Terre Plate, Part II: Courtillot’s Geomagnetic Excursion

There’s always a feeling of tristesse when they start pulling down the circus tents and loading the last of the elephants into their trailers. The last day of AGU feels a bit like that. AGU puts one much in mind of those medieval faires, or the Jokkmokk Vintermarknad, where people gathered (and still gather, in the latter case) from time to time to exchange goods and the latest news. Our own faire is a marketplace of ideas, though you can buy some nifty stuff here,too. Like a medieval faire, this is a social event as well — a time of feasting and revels, of renewing old friendships, and of making new ones. Happily, any brawls we have here are rather genteel ones.

But, it’s not over ’til it’s over especially in view of the fact that I was chairing (and giving the last talk at) the very last session of the whole shooting match — on evolution of extrasolar Large Earths. A dedicated group of extrasolar types stayed around for the fun. Closer to home, though, I dropped in on the session on Pliocene climate and the session on geoengineering.

[Read more…] about Rolling up the circus tent: Dispatch #7

Today was the all-Union session on Tipping Points, and several people have asked for comments on what went on there. I suppose this session might have been useful for people who had to miss the more detailed discussion in specialized sections, but I don’t have much to say about most of the talks, since they for the most part went over issues like ice sheet dynamics and rapid arctic sea ice loss, which I’ve discussed in earlier dispatches. Myself, I never found the notion of “tipping points” to be a very useful contribution to public discourse. The concept is ill-defined and very prone to be misunderstood — as in: we’ve passed a tipping point so it’s too late to do anything (might as well have a party). In Hansen’s talk, he did try to clarify what he meant by a tipping point. His notion of this has less to do with what mathematicians understand as “bifurcations,” and more to do with a kind of inertia in the climate system. He means things like having passed a threshold of CO2 which, given warming in the pipeline and the lifetime of CO2, commits a certain discrete event — e.g. loss of perennial sea ice or the Amazon rainforest– to occurring even if we were to later reduce emissions to zero. He tried to distinguish between reversible and irreversible tipping points. The talk was good cheerleading, after a fashion, but rather thin on real examples of what might be a tipping point in his definition. Everything he said was true (especially the emphasis on the importance of a rapid phase-out of coal burning) but the talk had much more to do with energy policy and lamentation of the power of entrenched fossil fuel interests than it had to do with climate science.
[Read more…] about Live (almost) from AGU–Dispatch #6

The summer of 2007 was apocalyptic for Arctic sea ice. The coverage and thickness of sea ice in the Arctic has been declining steadily over the past few decades, but this year the ice lost an area about the size of Texas, reaching its minimum on about the 16th of September. Arctic sea ice seems to me the best and more imminent example of a tipping point in the climate system. A series of talks aimed to explain the reason for the meltdown. [Read more…] about Notes from The Gathering #5: Arctic sea ice: is it tipped yet?

Ptarmigans are Back! Fans of the Sheep Albedo Feedback will remember these little fellows over on the right (photo credit: Ken Tape) from the immortal paper by Squeak and Diddlesworth on the influence of ptarmigan populations on the Laurentide Ice Sheet. In Session C33A on Wednesday, Ken Tape of the University of Alaska presented a paper on the influence of ptarmigan grazing on shrubbification of the Alaskan tundra. It seems that when there is deep snow cover, ptarmigan browsing is concentrated on those few willows that stick up above the snow. They eat the buds, which inhibits willow growth. These tall willows are the ones that have managed to benefit most by climate warming, but the ptarmigan provide a stabilizing feedback, up to a point. An interesting thing is the ptarmigan don’t like to perch. 98% of the winter buds within a half meter of the snow surface get eaten, but only 48% of the buds above that browse level. So, if the shrubs grow fast enough to get above the browse level, they can beat the ptarmigans. This seems to be happening more and more.
[Read more…] about Live (almost) from AGU–Dispatch #4

Just a few minutes ago Chappellaz et al presented the deepest dregs of greenhouse gas concentration data from the EPICA ice core in Antarctica, extending the data back to 800,000 years ago. In Al Gore’s movie you saw what was at that time the longest record of atmospheric greenhouse gas concentrations, back to 650 kyr, and their astonishing correlation with Antarctic temperature. This iconic superstar record has probably consumed as many eyeball-hours as any in climate science, alongside other classics such as the Jones et al. global temperature trends, the Moana Loa recent CO₂ record, and the hockey stick. The Antarctic CO₂ record has spawned countless internet rants about the CO₂ lag behind temperature, and the circle of cause and effect between CO₂ and climate. And the new data say … [Read more…] about Hot off the projector #3: Atmospheric CO₂ to 800 kyr ago

Before I get started with a few hasty remarks on today’s events, let me remind you that Lonnie Thompson’s Frontiers in Geophysics lecture will be webcast live on Wednesday at 1815 Pacific time. A link to the webcast can be found here. The lecture is entitled “Abrupt Climate Change and Our Future”. At the same page you’ll find links to Arvidson’s Whipple lecture on Mars exploration, which will be webcast at 14:20. Enjoy! Wish you were here.

Now, let me say at once how inspiring it is to see so much first-rate innovative science arrayed here. There are a lot of geophysicists in the world, and most of them are very, very good. It is especially encouraging to see so much new, young talent in all areas. I spend all too much of my time on RealClimate writing about bad science, it is great to come here and get a reality check.

[Read more…] about Live (almost) from AGU–Dispatch #2