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Tyndall Lecture: GC43I. Successful Predictions - 2012 AGU Fall Meeting

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Published on Dec 7, 2012

Tyndall Lecture: GC43I. Successful Predictions - 2012 AGU Fall Meeting

Abstract:

http://abstractsearch.agu.org/meeting...

In an observational science, it is not possible to test hypotheses through controlled laboratory experiments. One can test parts of the system in the lab (as is done routinely with infrared spectroscopy of greenhouse gases), but the collective behavior cannot be tested experimentally because a star or planet cannot be brought into the lab; it must, instead, itself {\it be} the lab. In the case of anthropogenic global warming, this is all too literally true, and the experiment would be quite exciting if it weren't for the unsettling fact that we and all our descendents for the forseeable future will have to continue making our home in the lab. There are nonetheless many routes though which the validity of a theory of the collective behavior can be determined. A convincing explanation must not be a"just-so" story, but must make additional predictions that can be verified against observations that were not originally used in formulating the theory. The field of Earth and planetary climate has racked up an impressive number of such predictions. I will also admit as "predictions" statements about things that happened in the past, provided that observations or proxies pinning down the past climate state were not available at the time the prediction was made. The basic prediction that burning of fossil fuels would lead to an increase of atmospheric CO2, and that this would in turn alter the Earth's energy balance so as to cause tropospheric warming, is one of the great successes of climate science. It began in the lineage of Fourier, Tyndall and Arrhenius, and was largely complete with the the radiative-convective modeling work of Manabe in the 1960's -- all well before the expected warming had progressed far enough to be observable. Similarly, long before the increase in atmospheric CO2 could be detected, Bolin formulated a carbon cycle model and used it to predict atmospheric CO2 out to the year 2000; the actual values come in at the high end of his predicted range, for reasons I shall discuss. During the dark ages of global change, between Arrhenius and Plass (punctuated by Callendar), work on planetary climate had not in fact ground to a halt, but developed vigorously in the astronomical community. This culminated in major discoveries about the atmospheres of Mars and Venus, notably Sagan's prediction that Venus has an extremely high surface temperature owing to an atmosphere extremely rich in greenhouse gases. The fertile interplay between astrophysics and terrestrial climate science continues in the current dawning era of exoplanet discovery. Early modeling work, notably by Manabe and co-workers, identified a number of spatial patterns of global change that were ultimately realized in data. These include: amplification of warming over land and in the Arctic, and the conjunction of stratospheric cooling with tropospheric warming. Additional examples I will discuss include the problem of tropical temperatures at the Last Glacial Maximum, water vapor feedback, Hansen's prediction of response to the Pinatubo eruption, and the prediction that ocean heat uptake would delay warming. While not all aspects of climate change were anticipated in advance (notably the interruption of warming around 1950-1970), examples of truly failed predictions are rare, and are overwhelmingly found among theories such as those of Angstrom or Lindzen which purport to show little sensitivity of climate to CO2.

Cite as: Author(s) (2012), Title, Abstract GC43I-01 presented at 2012 Fall Meeting, AGU, San Francisco, Calif., 3-7 Dec.

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