[Vision2020] It's The Physics, stupid...(Not a Good Debating Technique...)

[Ted Moffett]

http://www.realclimate.org

http://www.realclimate.org/index.php?p=207

18 December 2007
Les Chevaliers de l'Ordre de la Terre Plate, Part II: Courtillot's
Geomagnetic Excursion
Filed under: Climate Science— raypierre @ 9:44 AM - ()
This article continues the critique of writings on climate change by
Allegre and Courtillot, started in Part I .

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.

Raymond T. Pierrehumbert
Filed under: Contributor Bio's— raypierre @ 1:00 AM

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 is 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 currently writing a book on comparative planetary
climate, "Climate from First Principles," to be published by Cambridge
University Press.

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