There's no consensus on how serious the hole in the ozone layer is. You can actually still find people who dismiss it entirely, and you can find others who see the hole in the ozone layer as a doomsday machine that could wipe out life on Earth.
Neil Comins, professor of astronomy and physics at the University of Maine, takes a different approach. Like a chess player, he considers not just the next move, but the move after the next move. He knows that people do not agree on whether the hole in the ozone is a threat, but he nevertheless asks the next question: What would happen, based on what we know of physics and atmospheric chemistry, if the ozone layer itself were depleted by as much as, say, 25 percent?He grants that this may not happen, but as a scientist he believes that the odds that, under present circumstances, it will reach that level are somewhere between possible and likely.
To understand the consequences of depleting the ozone layer by 25 percent, it helps to know a little more about what the ozone layer does. The ozone layer shields us from the ultraviolet radiation that would otherwise make life on earth impossible. If you've ever had a bad sunburn, you know what even very small amounts of ultraviolet radiation can do.
The ozone layer extends from about nine miles to about 30 miles above the Earth's surface. You might expect that because the ozone layer is more than 20 miles thick, we could easily afford to lose some. However, part of the reason scientists worry about the ozone layer is that in spite of how deep it is, there's still astonishingly little of it considering it makes life possible. As Comins points out, "There is so little ozone surrounding the Earth that if all of it were compressed to the density of the air we breathe, it would make a layer less than one-eighth of an inch thick."
The ozone hole has begun forming during the Antarctic winter. Man-made compounds containing chlorine and bromine drift from Earth into the stratosphere and then become trapped there by an atmospheric whirlpool called the Antarctic Vortex. By late October, which is spring there, the Antarctic Vortex breaks up. At this point, the ozone hole fills in as ozone from other parts of the stratosphere drifts southward.
"In other words," Comins explains, "each year some of the ozone that is over your head goes south to plug the renewed Antarctic ozone hole." This is ominous because each year the ozone layer over us thins a little bit more.
If it were depleted by 25 percent, it would create a condition that would cause a major disruption in the food chain.
The world's food chain begins with microscopic plants called phytoplankton. These rely on the sun's energy to help convert inorganic compounds into food. Because phytoplankton are so small, they are profoundly more vulnerable to radiation than larger creatures. The intense radiation resulting from 25 percent less ozone would be enough to kill vast numbers of them.
Animals further up the food chain that feed on phytoplankton would find their food source abruptly depleted as the radiation level rises. Many of these animals would go extinct. At the top of the food chain, man would face famine on a scale unknown before.
"Where do we go from here?" asks Comins. "By stopping CFC and halon production now, we may keep the total ozone depletion down to 10 percent rather than 25 percent. We all have a stake in the result, and we had better act soon."
(Mitzi Perdue writes about environmentally related matters weekly for Scripps Howard News Service.)