Severe storms cause widespread destruction on the ground, but a new study says they may also be damaging protective ozone in the upper atmosphere. A team of Harvard University scientists has found that water vapor ejected into the stratosphere by strong thunderstorms can set off an ozone-depleting chemical reaction.
The study, published July 26, raises concerns that climate change might accelerate the loss of ozone above Earth’s populated areas. Until now, it was thought that human-induced ozone depletion only occurred at very cold temperatures above the planet’s polar regions. But this research shows that ozone is vulnerable above more temperate climates as well.
Such a possibility poses risks to humans: the ozone layer protects us by blocking a large portion of the sun’s harmful ultraviolet (UV) rays, known to cause skin cancer. Scientists are concerned that ozone depletion over the planet’s populated areas could increase as a warming climate loads the dice for more frequent severe weather.
James G. Anderson, lead author of the study, explains that ozone depletion can occur when towering cumulonimbus clouds in strong thunderstorms punch through the tropopause – the boundary layer separating the lower atmosphere from the stratosphere.
Updrafts in these storms accelerate water vapor as high as 9 to 12 miles above us in a process called convective injection. Anderson and his colleagues found that in areas where water vapor was injected into the stratosphere, the surrounding loss of ozone increased significantly. This is because water vapor raises the temperature at which chlorine – a byproduct of now-banned CFCs, or chlorofluorocarbons – undergoes a chemical chain reaction that ends up attacking ozone.
In its own summary of Anderson’s findings, ScienceNews writes:
“… the havoc wreaked by water vapor could continue for days after a storm, as humidity levels slowly fall. As much as 25 to 35 percent of ozone, over a horizontal distance of 100 kilometers, could be annihilated in a week.”
More research is still needed to measure actual rates of stratospheric ozone depletion due to convective water vapor. Nonetheless, this study implies that Earth’s protective ozone layer may not be repairing itself as quickly as hoped in the wake of the 1987 Montreal Protocol that banned manmade CFCs.
If severe storms are in fact pumping extra water vapor into the stratosphere, we may not be as protected from the sun’s damaging UV rays as once thought.