for National Geographic News
Laughing gas—known to scientists as nitrous oxide—is now the biggest threat to Earth's ozone layer, according to a new study.
The ozone layer, part of Earth's upper atmosphere, protects plants and animals from harmful ultraviolet radiation from the sun.
In 1987 countries around the world united to ban chlorofluorocarbons, or CFCs—gases that were commonly used in refrigerators and air conditioners. These gases made their way into the atmosphere and thinned the ozone layer by about 5 percent worldwide.
CFC emissions drastically dropped following the ban, and the ozone layer has been on track to largely recover by mid-century, according to the World Meteorological Organization.
But nitrous oxide emissions, which are being released at a rate of about ten million tons a year, may thwart that progress.
An expansion in farming and soaring numbers of livestock may increase emissions of the gas, which comes mostly from fertilizer and animal waste.
"The ozone layer would be prevented from recovering by the time we thought it would," said study leader A. R. Ravishankara of the National Oceanic and Atmospheric Administration in Boulder, Colorado.
Using a computer simulation of the atmosphere, Ravishankara and colleagues calculated how big of an effect nitrous oxide will have on the ozone layer.
The team found that nitrous oxide's effect is as potent as it is for many of the banned CFCs.
Nitrous oxide emitted today will have a lasting effect: "The overall lifetime of nitrous oxide is about a hundred years, comparable to many CFCs," Ravishankara said.
Chlorofluorocarbons, which are still found in the atmosphere, continue to damage the ozone layer.
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