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Broadly Misleading

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Just when we were beginning to think the media had finally learned to tell a hawk from a handsaw when covering global warming (at least when the wind blows southerly), along comes this article ‘In Ancient Fossils, Seeds of a New Debate on Warming’ by the New York Times’ William Broad. This article is far from the standard of excellence in reporting we have come to expect from the Times. We sincerely hope it’s an aberration, and not indicative of the best Mr. Broad has to offer.

Broad’s article deals with the implications of research on climate change over the broad sweep of the Phanerozoic — the past half billion years of Earth history during which fossil animals and plants are found. The past two million years (the Pleistocene and Holocene) are a subdivision of the Phanerozoic, but the focus of the article is on the earlier part of the era. Evidently, what prompts this article is the amount of attention being given to paleoclimate data in the forthcoming AR4 report of the IPCC. The article manages to give the impression that the implications of deep-time paleoclimate haven’t previously been taken into account in thinking about the mechanisms of climate change, whereas in fact this has been a central preoccupation of the field for decades. It’s not even true that this is the first time the IPCC report has made use of paleoclimate data; references to past climates can be found many places in the Third Assessment Report. What is new is that paleoclimate finally gets a chapter of its own (but one that, understandably, concentrates more on the well-documented Pleistocene than on deep time). The worst fault of the article, though, is that it leaves the reader with the impression that there is something in the deep time Phanerozoic climate record that fundamentally challenges the physics linking planetary temperature to CO2. This is utterly false, and deeply misleading. The Phanerozoic does pose puzzles, and there’s something going on there we plainly don’t understand. However, the shortcomings of understanding are not of a nature as to seriously challenge the CO2.-climate connection as it plays out at present and in the next few centuries.

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Kristof on the Apocalypse

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We have noted with pleasure Nicholas Kristof’s column, The Big Burp Theory of the Apocalypse (TimesSelect subscription required), which appeared in the New York Times of 18 April. This column is built around the possibility of a catastrophic methane release from marine clathrate decomposition, but at heart it is really a lament that the more conventional and better understood harms of global warming have not proved sufficient to get the attention of the White House or Congress. This column is a refreshing change from the recent spate of backlash columns by Will, Novak and Lindzen attempting to tar climate scientists with the “a****mist” epithet.

Kristof gives a generous tip of the hat to “the excellent discussion of methane hydrates by scholars at www.realclimate.org.” (Thanks, Nick.) He has clearly made good use of Dave Archer’s RealClimate article on clathrates, and it shows in the Kristof’s sound discussion of the basic science. He is very clear on why a clathrate catastrophe would be a bad thing, but equally clear about the uncertainties. The column even contains an intelligent discussion of the Paleocene-Eocene Thermal Maximum as a possible example of a clathrate catastrophe. taking care to point out that this event might not, in fact, have been caused by methane release. Quite a lot to get in a short column, while still managing to achieve a lively style that surely keeps the readers awake.

Perhaps closest to our hearts is Kristof’s cogently stated theme that uncertainty is in the nature of the science, and is no excuse for inaction — indeed should be a spur to greater action. “The White House has used scientific uncertainty as an excuse for its paralysis. But our leaders are supposed to devise policies to protect us even from threats that are difficult to assess precisely — and climate change should be considered even more menacing than a nuclear-armed Iran.” He concludes, “The best reason for action on global warming remains the basic imperative to safeguard our planet in the face of uncertainty, and our leaders are failing wretchedly in that responsibility.”

Kristof is a 2006 winner of the Pulitzer Prize for commentary. Congratulations, Nick! We hope you keep on reading RealClimate.

Happy Birthday, Charles Darwin!

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Charles Darwin was born on February 12, 1809. The events commemorating Darwin’s birthday anniversary last Sunday, together with the recent conclusion of an important court case concerning the teaching of Intelligent Design (ID) in public schools prompts me to some musing concerning the relation of the Evolution/ID dialog to similar issues arising in connection with anthropogenic global warming. The age of the two theories is similar as well: Darwin introduced his theory in 1859, whereas Fourier initiated the study of the effect of atmospheres on climate with his 1821 treatise, stimulating the chain of developments leading to Arrhenius’ enunciation in 1896 of the theory that human influences on the atmosphere’s CO2 content could change the climate.

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Natural Variability and Climate Sensitivity

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One of the central tasks of climate science is to predict the sensitivity of climate to changes in carbon dioxide concentration. The answer determines in large measure how serious the consequences of global warming will be. One common measure of climate sensitivity is the amount by which global mean surface temperature would change once the system has settled into a new equilibrium following a doubling of the pre-industrial CO2 concentration. A vast array of thought has been brought to bear on this problem, beginning with Arrhenius’ simple energy balance calculation, continuing through Manabe’s one-dimensional radiative-convective models in the 1960’s, and culminating in today’s comprehensive atmosphere-ocean general circulation models. The current crop of models studied by the IPCC range from an equilibrium sensitivity of about 1.5°C at the low end to about 5°C at the high end. Differences in cloud feedbacks remain the principal source of uncertainty. There is no guarantee that the high end represents the worst case, or that the low end represents the most optimistic case. While there is at present no compelling reason to doubt the models’ handling of water vapor feedback, it is not out of the question that some unanticipated behavior of the hydrological cycle could make the warming somewhat milder — or on the other hand, much, much worse. Thus, the question naturally arises as to whether one can use information from past climates to check which models have the most correct climate sensitivity.

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Busy Week for Water Vapor

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It’s been a busy week for water vapor, and I have two recent papers to discuss. The first is the paper "Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe" by Rolf Philipona et al. (GRL, 2005, subscription required for full text), which has attracted a certain amount of media attention. The overall goal of the paper is to understand, from a physical standpoint, why European temperatures have been increasing three times faster than the Northern Hemisphere average. It focuses on the changes between 1995 and 2002, over which time good surface radiation budget observations are available. The paper reports some results on the role of large scale circulation changes (which they conclude are minor) but I’ll concentrate on the results relating to water vapor.

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Raymond T. Pierrehumbert

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Pierrehumbert Portrait
Raymond Pierrehumbert is the Louis Block Professor in Geophysical Sciences at the University of Chicago, having earlier served on the atmospheric science faculties of MIT and Princeton. He is principally interested in the formulation of idealized models which can be brought to bear on fundamental phenomena governing present and past climates of the Earth and other planets. His recent research interests have included water vapor feedback, baroclinic instability, the Neoproterozoic Snowball Earth, the climate of Early Mars, and methane hydrological cycles on Titan. He has been director of the Climate Systems Center, a US National Science Foundation Information Technology Research project aimed at bringing modern software design techniques to the problem of climate simulation. He has also collaborated with David Archer on the University of Chicago’s global warming curriculum.

He received an A.B. degree in Physics from Harvard, was then a Knox Fellow in the Department of Applied Mathematics and Theoretical Physics at Cambridge University, and completed his PhD on hydrodynamic stability theory at MIT, in the Department of Aeronautics and Astronautics. He was a lead author of the IPCC Third Assessment Report, and a co-author of the National Research Council study on abrupt climate change. He is a Fellow of the American Geophysical Union.

Pierrehumbert is the author of the textbook Principles of Planetary Climate, available from Cambridge University Press.

More information about his research, including a complete publication list, can be found here.