Summer storms in the United States inject water into the atmosphere at altitudes up to 20 kilometres, accelerating ozone-destroying reactions.

RICK D’ELIA/CORBIS

Storms may speed ozone loss above the United States

Injection of water vapour makes ozone layer sensitive to global warming and geoengineering.

Summer thunderstorms across the United States inject water vapour far higher into the atmosphere than was previously believed, promoting a cascade of chemical reactions that could pose an increased threat to Earth’s protective ozone layer as the climate warms.

Anderson’s team expected to see summer storms supply cirrus clouds by pumping water vapour up to an average altitude of about 14 kilometres. Instead, the researchers report today inScience¹, about half of the storms that they studied injected vapour to altitudes of between 15 and 20 kilometres.

“We were shocked,” says Anderson. “Standard, run-of-the-mill Midwestern thunderstorms are far more capable of injecting water vapour into the stratosphere than we once thought.”

There are significant implications for stratospheric ozone, which shields the Earth from ultraviolet radiation. Ozone can be destroyed by reactions with chlorine and water — and the rates of those reactions are governed mainly by temperature and the presence of water vapour. If, as expected, storm activity increases owing to global warming, says Anderson, the proportion of water in the stratosphere will increase, leading to accelerating destruction of stratospheric ozone — and an increase in the amount of ultraviolet radiation reaching Earth.

The affected area of the stratosphere — between 15 and 20 kilometres in altitude — contains about 20% of the total stratospheric ozone, and Anderson says that the water-vapour injections could provide conditions for rapid ozone destruction similar to those that scientists have been investigating for decades in Antarctica and more recently in the Arctic.