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The Ozone Layer:

South Polar Ozone Hole, 1997

From http://jwocky.gsfc.nasa.gov/eptoms/epanim97.html

"This [animated .gif] movie shows a sequence of daily images of the southern hemisphere using an orthographic projection looking down on the earth from 60 degrees south latitude. The ozone hole is indicated by ozone values less than 225 Dobson units (the violet colors).

"The black circle in the middle is due to polar night, when [the] T[otal] O[zone] M[apping] S[pectrometer] [satellite] cannot measure ozone. Notice that its size decreases and then disappears as the apparent position of the sun crosses the equator (signalling the start of spring in the northern hemisphere) and more and more of Antarctica becomes sunlit. The other black gaps are due to the fact that the Earth Probe is in a 500 kilometer orbit and cannot, therefore, provide full daily global coverage for ozone measurements within 60 degrees of the equator.

"The discontinuity that is sometimes seen at the international date line (180 degrees longitude) is due to the fact that data on the east side of the line (negative longitudes) are taken up to 24 hours later than the west side of the line (positive longitudes).

"Due to a problem with the satellite, there is no data for 17-November-97 and 18-November-97."

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Jason has a strong argument--but this may well be one of those cases in which certainty-equivalent analyses are a bad idea, and risk and uncertainty are surely not the friends of global-warming skeptics.

Moreover, even if the U.S. is by and large unaffected on net, and even if Canada gains bigtime from global warming, there are other places that don't: Bangladesh for example, as a warmer earth means bigger and more frequent typhoons. Their losses may well be small in *monetary* terms, but money benefits and damages ain't social welfare.

So far the atmostpheric CO2 measurements are not suggesting a big win for the ocean-will-rapidly-take-it-all-up crowd...

Contributed by Brad De Long (delong@econ.berkeley.edu) on May 23, 2000.

Regarding global warming, the more sophisticated skeptics such as Patrick Michaels of the University of Virginia argue that indeed there will be global warming, but that a) it will not be as great as some have forecast and b) it will mostly occur at night during winters, thus of little economic or social significance. The other problem is that satellite measures of air temperature suggest very little warming, in contrast to ground measures that are subject to "urban heating" bias and other problems. This is an unresolved scientific problem. There are a variety of other loose ends in the scientific debate, negative feedbacks such as oceanic uptake of carbon and the acceleration of plant growth. Jason Shogren, now at University of Wyoming and formerly environmental adviser to the CEA during the Kyoto negotiations has argued that the only way there is a benefit/cost ratio greater than on for the Kyoto Accords is if there is reasonably high probability of a true catastrophe in the next century. Arguments for such a probability may involve the positive feedbacks associated with albedo effects, the reflectivity off the snow and ice caps, that may have been responsible for the (relatively geologically) rapid movements of the planet into and out of ice ages. We may be in such a period now with melting feeding back into warming as sunlight is reflected less and less. This could be the trigger for a sudden warmup leading to a serious glacier melt and ice cap falloff into the oceans, either in Anatarctica or more likely off of Greenland

Contributed from by J. Barkley Rosser, Jr. (rosserjb@jmu.edu) on May 22, 2000.

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Professor of Economics J. Bradford DeLong, 601 Evans Hall, #3880
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