Strong summer storms that pump water high into the upper atmosphere pose a threat to the protective ozone layer over the United States, researchers said Thursday, adding that the risk of damage may increase as the climate warms.
In a study published online by the journal Science, Harvard University scientists reported that some storms send water vapor well into the stratosphere and showed how such events could rapidly set off ozone-destroying reactions with chemicals that remain in the atmosphere from CFCs, the now-banned refrigerant gases.
Ozone helps shield people, animals and crops from damaging ultraviolet rays from the sun. Much of the concern about the ozone layer has focused on Antarctica, where a seasonal thinning has been seen for two decades, and the Arctic, where a hole was observed last year. But those regions have almost no population.
A thinning of the ozone layer over the United States during summers could mean an increase in ultraviolet exposure for millions of people and a rise in the incidence of skin cancer, the researchers said.
This problem now is of deep concern to me, said James Anderson, an atmospheric scientist and the lead author of the study. I never would have suspected this.
The findings were based on sound science, he and other experts said, but direct measurements of the impact of water vapor on ozone chemistry are lacking, and much more research is needed.
The NASA-financed study focused on the United States because that is where the data was collected. But the researchers pointed out that similar conditions could exist at other midlatitude regions.
It is chlorine from the CFCs that ultimately destroys ozone. The chlorine has to undergo a chemical shift in the presence of sunlight that makes it more reactive, and this shift is sensitive to temperature.
Anderson and his colleagues found that a significant concentration of water vapor raises the air temperature enough in the immediate vicinity to allow the chemical shift, and the ozone-destroying process, to proceed rapidly.
The rate of these reactions was shocking to us, Anderson said.