More On The Unsettled Nature Of Settled Science

Twenty years ago we so confident in our understanding of how ozone holes formed that we banned certain chlorofluorocarbons because they destroyed the ozone layer. The chemist who alerted the world won a Nobel Prize. But, it turns out that it was all wrong.

"This must have far-reaching consequences," Rex says. "If the measurements are correct we can basically no longer say we understand how ozone holes come into being." What effect the results have on projections of the speed or extent of ozone depletion remains unclear.

The rapid photolysis of Cl2O2 is a key reaction in the chemical model of ozone destruction developed 20 years ago2 (see graphic). If the rate is substantially lower than previously thought, then it would not be possible to create enough aggressive chlorine radicals to explain the observed ozone losses at high latitudes, says Rex. The extent of the discrepancy became apparent only when he incorporated the new photolysis rate into a chemical model of ozone depletion. The result was a shock: at least 60% of ozone destruction at the poles seems to be due to an unknown mechanism, Rex told a meeting of stratosphere researchers in Bremen, Germany, last week.


Other groups have yet to confirm the new photolysis rate, but the conundrum
is already causing much debate and uncertainty in the ozone research community. "Our understanding of chloride chemistry has really been blown apart," says John Crowley, an ozone researcher at the Max Planck Institute of Chemistry in Mainz, Germany.

"Until recently everything looked like it fitted nicely," agrees Neil Harris, an atmosphere scientist who heads the European Ozone Research Coordinating Unit at the University of Cambridge, UK. "Now suddenly it's like a plank has been pulled out of a bridge." ...

Nothing currently suggests that the role of CFCs must be called into question, Rex stresses. "Overwhelming evidence still suggests that anthropogenic emissions of CFCs and halons are the reason for the ozone loss. But we would be on much firmer ground if we could write down the correct chemical reactions."

Oops!

It's not as though the Nobel Committee hasn't screwed up before. And more than once.