Monday, October 21st 2019, 8:00 pm – The recovery of the ozone hole got a little boost this year from some unusually warm weather
The 2019 Antarctic ozone hole is the smallest on record since the 1980s, according to NASA.
Each year, as the Antarctic emerges from the darkness of winter, frigid polar stratospheric clouds are suddenly exposed to sunlight, setting off a flurry of chemical reactions.
The molecules that help form these clouds, called chlorofluorocarbons (CFCs), break down in the sunlight, and the resulting components eat away at the protective layer of ozone molecules high above the continent.
This process destroys ozone far faster than it is created naturally by sunlight, and it results in the Antarctic ozone hole.
The average size and shape of the Antarctic ozone hole, so far in October 2019. Credit: NASA
Discovered in 1985, the Antarctic ozone hole forms each year between August to December. Growing to a peak size sometime in September, it then slowly closes up again in the following months, only to re-form the next year. Usually, depending on the weather, the size of the hole varies from year to year.
When scientists first discovered it, they found that the hole was growing at an alarming pace, due to the release of chlorofluorocarbons into the atmosphere. These chemicals were once widely used as accelerants in spray cans and as coolants in refrigerators and air conditioners. Moving quickly, the scientists gathered their evidence and went to the world’s governments. Within two years, the 1987 Montreal Protocol had been signed, banning the production and use of CFCs.
Since then, careful yearly tracking of the ozone hole has revealed that our decisive action halted its growth by the late 1990s. While it took a few decades to see progress after that, NASA has seen a definite trend towards smaller and smaller ozone holes.
For 2019, the Antarctic ozone hole reached its largest extent of the year on September 8, at an area of 16.4 million square kilometres. In the weeks after, the hole then shrank significantly, to an average of around 10 million square kilometres.
So far, that is the smallest maximum extent we have ever seen from the ozone hole since its discovery, and the smallest ozone hole seen in September and October since the year 1982!
The maximum extent of the 2019 stratospheric ozone hole, on September 8, 2019. Credit: NASA
By comparison, the largest ozone hole ever recorded was on September 9, 2000, at 29.9 million sq km. The maximum extent of the ozone hole in 2018 was 24.8 million sq km, on September 20.
RARE WONKY WEATHER
This year’s new record for smallest ozone hole is more encouraging news for the recovery of the ozone layer, but it isn’t exactly normal.
According to NASA, the reason for the smaller ozone hole this year was an unusual pattern of warmer temperatures in the stratosphere. Temperature readings from the Antarctic stratosphere in September were the warmest they’d been in 40 years of record-keeping, at around 15°C above normal.
This warmth limited the formation of the frigid polar stratospheric clouds – where most of the ozone-destroying chemical reactions take place – and those clouds that did form did not last as long as usual.
At the same time, the warming also knocked the southern polar vortex off-kilter.
Similar to how warmer Arctic temperatures can slow the northern polar vortex, causing a wide swath of frigid air to extend down over North America, this same situation occurred in the south. A lobe of the southern polar vortex extended far north towards the southern tip of Argentina, while more ozone-rich air moved in behind to fill in the space over East Antarctica.
According to NASA, there’s no link here to anthropogenic climate change, although this situation is highly unusual.
“It’s a rare event that we’re still trying to understand,” said Susan Strahan, a NASA Goddard scientist from the Universities Space Research Association. “If the warming hadn’t happened, we’d likely be looking at a much more typical ozone hole.”
WHY DOES THIS MATTER?