Re: naturalSCIENCE Cover Story of October 8, 1997
From: S. Fred Singer
Date: Tue, 17 Mar 1998 15:59:44 -0500
Reply To: firstname.lastname@example.org
Subject: Stratospheric Ozone Depletion
Stratospheric Ozone Depletion: 10 Years After Montreal
I wish to comment on your cover story of October 8, 1997.
The stratospheric ozone layer is important because, among other things, it reduces the amount of solar ultraviolet-B radiation reaching the Earth's surface. UV-B is the main cause of basal and squamous cell skin cancers, but not of malignant melanoma; the latter is primarily caused by UV-A--which is not absorbed by ozone. UV-B is not known to cause other effects on human health, or problems for agriculture or forest growth or ecosystems. The easiest way to gain perspective on this issue is to note that UV-B increases rapidly towards lower latitudes, by 5000% between polar regions and equator, mainly because of the sun angle. A 10% decrease in ozone, causing a 20% increase in UV-B, would therefore correspond to a move of 120 miles towards the equator.
The actual observations of global stratospheric ozone depletion are somewhat uncertain. Published claims (in Science, 262:1032, 1993) that UV-B is increasing at 35% per year were later shown to be false (Science, 264:1341, 1994) The Antarctic Ozone Hole did grow rapidly between 1975 and 1985, but has more or less stabilized since then, subject to large interannual fluctuations.
The decision to phase out methyl bromide is curious, and seems to be ideologically motivated. About two-thirds of methyl bromide present in the atmosphere is of natural origin. No one has yet observed an increasing trend of bromine in the stratosphere, which would indicate a human influence. In addition, the atmospheric lifetime of methyl bromide is less than one year. If a problem should arise, production can be stopped and anthropogenic methyl bromide will rapidly disappear from the atmosphere.
Finally, I am surprised at the conservative economic estimates by Canada's Environment Minister. The Canadian study purports to show a global benefit-to-cost ratio of 2:1 for ozone layer protection. The United States does things on a grander scale. As reported to Congress in 1995, EPA's benefit-to-cost ratio is 1,000:1, based on estimated costs on the order of $30 billion and health benefits of up to $32 trillion(!). For once, I share the skepticism of the activist Ozone Action group, which doubts the realism of the benefit calculations.
S. Fred Singer
1 Dr. Singer, an atmospheric physicist, is the president of the Science & Environmental Policy Project based in Fairfax, Virginia. He is emeritus professor of environmental sciences at the University of Virginia and former director of the U.S. Weather Satellite Service.