July 3, 2006 — Despite widespread international reductions in ozone destroying chemicals, the Antarctic ozone hole will likely continue its annual appearance for another 60 years, say atmospheric scientists – 20 years longer than previous estimates.
A new model that analyzes the effects of ozone gobbling chlorofluorocarbon (CFC) emissions predicts a return to pre-1980 stratospheric ozone levels over the southern continent in the year 2068. What’s more, no meaningful shrinking of the ozone hole should be expected before 2024, say researchers from NASA, NOAA and the National Center for Atmospheric Research in the latest issue of Geophysical Research Letters.
"The (previous) models underestimated the amount of chlorine and bromine over Antarctica," said NASA atmospheric scientist Paul Newman, referring to the two elements that tear ozone apart. "That’s why we under-estimated the recovery rate."
One reason for earlier miscalculation is that CFC quantities over Antarctica were originally measured indirectly, by how much ozone destruction they caused. But when far more chlorine and bromine is present than needed to destroy all the ozone over Antarctica, it's difficult to predict the consequence of such a surplus.
In the 1990s the stratosphere over Antarctica saw the first of this sort of "saturation effect," said Newman, with 100 percent ozone destruction and plenty of chlorine and bromine to spare.
There can be no significant change in ozone destruction until the levels of harmful chemicals at least drop below the saturation level. The new model estimates that will happen by 2018, with a detectable reduction in ozone destruction by 2024.
"Now we understand how the models were wrong," Newman told Discovery News.
Another change to the model comes from new information on how long it takes chlorine-containing CFCs to reach the Antarctic stratosphere and how long they linger, says atmospheric researcher John Austin of NOAA’s Geophysical Fluid Dynamics Laboratory and the UK’s Meteorological Office.
"Over the last few years we’ve realized that it takes a lot longer for the chlorofluorocarbons to be taken out of the atmosphere," said Austin. The longer they linger, the slower the ozone recovers.
Yet another concern that has been raised in recent months is that the amounts of CFCs still being emitted hasn’t dropped off as quickly as expected. That could possibly add more delays to ozone recovery at both poles.
"In principle you could have another delay of another couple of decades," said Austin. "You keep adding more and more delays and you’re starting to look at another 30 years. That’s a problem."
