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Climate change could produce an ozone hole over the U.S. similar to the one observed over Antarctica, above, in 2006. Image via NASA

For the past 25 years, it seemed that we’d pretty much solved the ozone problem. In the 1970s and 80s, people around the world grew increasingly alarmed as research revealed that chemicals we were producing—such as CFCs, used in refrigeration— had started destroying the crucial ozone layer, high up in the atmopshere, that protects us from the sun’s harmful UV radiation. In response, world governments came together to sign the Montreal Protocol in 1987, which phased out the production of ozone-depleting chemicals. The concentration of these chemicals in the atmosphere leveled off within a decade.

Yesterday, though, Harvard scientists hit us with some bad news: It looks as if climate change could actually cause the depletion of the ozone layer to resume on a wide scale, with grim implications for the United States.

“If you were to ask me where this fits into the spectrum of things I worry about, right now it’s at the top of the list,” said professor James Anderson in a press release, discussing his team’s paper, published online in Science. “What this research does is connect, for the first time, climate change with ozone depletion, and ozone loss is directly tied to increases in skin cancer incidence, because more ultraviolet radiation is penetrating the atmosphere.”

The revelation comes from the researchers’ observation that warm-temperature summer storms can force moisture high up into the stratosphere, a layer of the atmosphere that sits about 6 miles above our heads. Typically, storm updrafts are halted at a boundary just below the stratosphere, but in a series of observation flights above the U.S., the team saw that storms with sufficient power injected water vapor into the stratosphere via convection currents.

Normally, the stratosphere is bone dry. In the Arctic and Antarctic, though, the presence of holes in the ozone layer is tied to moisture. Because water vapor raises the air temperature in the immediate vicinity, it allows compounds such as chlorine—leftover from CFCs, which will remain in our atmosphere for decades—to undergo a chemical shift into a free radical form, which then depletes ozone. In the warmer air above the U.S., the researchers measured that the local presence of water vapor increased the rate of ozone erosion as high as one hundredfold.

Because this mechanism has only been detected now, there are no historical data about how much water vapor has been moved upward by such storms over time, and so the researchers can’t say just how much total increased ozone depletion has occurred so far. But their concern is the future. The problem is that, as previous studies have shown, climate change is likely to mean more warm-temperature storms, especially over populated mid-latitude regions such as ours.

As a result, despite the best efforts of the Montral Protocol, the erosion of the ozone layer might accelerate in the coming century. The particularly troubling aspect of this discovery is that it puts highly-populated areas at risk, as compared to the polar regions previously observed.

“There has been a major effort by the medical community to define the relationship between decreases in ozone and the subsequent increases in skin cancer,” Anderson said. “The answer is quite clear–if you multiply the fractional decrease in ozone protection by about three, you get the increase in skin cancer incidence. There are 1 million new skin cancer cases in the U.S. annually–it’s the most common form of cancer, and it’s one that’s increasing in spite of all the medical research devoted to it.”

Much more field research is needed to track the rate of water vapor injections into the stratosphere, the attendant ozone depletion and the prevalence of skin cancer in the U.S. population. But as long as greenhouse gas emissions rise, the trend will likely continue. “We don’t know how rapidly the frequency and intensity of these storms will increase, so we can’t place a time scale on this problem, but the core issue here is quite straightforward and simple, because we understand this chemistry,” said Anderson

“In my mind, this is not just a broad public health issue,” Anderson added. “This is about actually being able to step out into the sunlight.”