The loss of ozone over Antarctica in the southern hemisphere is relatively well documented and popularly known, especially within Australia where for residents of southern states (like the island state of Tasmania) venturing out into the sun during summer is downright dangerous.
Simply put, conditions in the Arctic — on the other side of the planet — are not conducive to ozone loss.
However, in 2011, that’s exactly what happened, when ozone levels in the atmosphere over the Arctic were 20% less than the average.
Ozone loss requires three key ingredients we as humans produce — chlorine from man-made chlorofluorocarbons (CFCs), frigid temperatures and sunlight. These three ingredients are not normally present in the Arctic atmosphere at the same time.
A new study by NASA, however, has found that while chlorine in the Arctic atmosphere was the primary culprit for what has become known as the Arctic ozone hole of 2011, unusually cold and persistent temperatures also helped the ozone depletion. On top of that, uncommon atmospheric conditions blocked wind-driven transport of ozone from the tropics, which subsequently halted the supply of ozone until April.
“You can safely say that 2011 was very atypical: In over 30 years of satellite records, we hadn’t seen any time where it was this cold for this long,” said Susan E. Strahan, an atmospheric scientist at NASA Goddard Space Flight Center in Greenbelt, Md., and main author of the new paper, which was recently published in the Journal of Geophysical Research-Atmospheres.
“Arctic ozone levels were possibly the lowest ever recorded, but they were still significantly higher than the Antarctic’s,” Strahan said. “ There was about half as much ozone loss as in the Antarctic and the ozone levels remained well above 220 Dobson units, which is the threshold for calling the ozone loss a ‘hole’ in the Antarctic – so the Arctic ozone loss of 2011 didn’t constitute an ozone hole.”