Higher temperatures over Antarctica this year shrank the hole in the ozone layer to the smallest it's been since 1988.
The ozone hole is a depletion of ozone gas (O3) in the stratosphere above Antarctica. The three-oxygen molecule is toxic at ground level, but high in the atmosphere, it deflects dangerous ultraviolet rays from reaching Earth's surface.
In 1985, scientists first detected the hole in the ozone layer and realized it was being caused by man-made chlorine and bromine, often found in chlorofluorocarbons (CFCs), compounds used as refrigerants. In 1987, the Montreal Protocol initiated the phase-out of these chemicals. As they gradually leave the atmosphere, the ozone hole will heal, and scientists expect it to return to 1980s size by 2070.
Natural variability affects this healing year-to-year, however.
"The Antarctic ozone hole was exceptionally weak this year," Paul Newman, chief scientist for Earth Sciences at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. "This is what we would expect to see given the weather conditions in the Antarctic stratosphere." [Infographic: Earth's Atmosphere Top to Bottom]
Weather and ozone
In the upper atmosphere, CFCs break apart, freeing chlorine to react with ozone molecules, a reaction that creates oxygen and chlorine monoxide. Similar reactions occur with bromine. Polar stratospheric clouds, which form in frigid temperatures, speed up this process by providing surfaces for the reactions to occur on. That's why the ozone hole worsens in the Southern Hemisphere winter.