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Graphic showing the Antarctic ozone on September 16, 2013.

The Antarctic ozone hole reached its maximum single-day area for 2013 on Sept. 16. The ozone hole (purple and blue) is the region over Antarctica with total ozone at or below 220 Dobson units (a common unit for measuring ozone concentration).

GRAPHIC COURTESY NASA'S GODDARD SPACE FLIGHT CENTER

Olive Heffernan in San Francisco

for National Geographic

Published December 13, 2013

Last year the hole in the ozone layer above Antarctica was surprisingly small. But don't get used to that, say atmospheric scientists. Rather than signaling a speedy recovery, the shrinkage was likely a sign of variable weather.

The ozone hole still has decades of waxing and waning before it finally closes, suggests research presented this week at a American Geophysical Union meeting. (Also see "Ozone Depletion".)

“The hole should vanish entirely by 2070 and should start to recover in the next decade,” says one of the lead scientists on the research, Susan Strahan of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The size of the ozone hole above Antarctica, a region in the upper atmosphere characterized by very low ozone levels, has peaked in recent years, covering roughly 8.1 million square miles (21 million square kilometers) to 10.4 million sq. mi. (27 million sq. km.)—an area larger than South America.

More than 20 years ago the Montreal Protocol limited the use of ozone-depleting chemicals, which had left a visible wound in the Earth’s ozone layer. But since they have a life span of more than 100 years, these chemicals are still thinning the the upper atmosphere’s ozone layer.

This layer matters because it shields the Earth's surface from the sun's ultraviolet radiation, which can cause skin cancer and cataracts in people. That’s why the hole’s pattern of recovery and relapse has left scientists disappointed—and puzzled.

Two of the deepest and largest ozone holes of the past decade occurred in 2006 and 2011, for example, yet the hole in 2012 was the second smallest of the past 20 years.

Strahan and her colleagues Anne Douglass and Natalya Kramarova, also at NASA’s Goddard Space Flight Center, now think they know why. They say the hole contracts and expands not only in response to the level of ozone-depleting chemicals left in the atmosphere but also in response to wind.

“It’s very important to understand these year-to-year changes”, says Lorenzo Polvani, an atmospheric scientist at Columbia University in New York, who was not involved in the study.

Vertical Reality

Traditionally, scientists have measured the total amount of ozone in the atmosphere from top to bottom, then used those measurements to produce a single indicator of ozone recovery. But using newly available data from two satellites, Strahan and Kramarova were able to see what was happening inside the hole.

Image showing a cross-section of Earth's ozone layer as measured by the limb profiler, part of the Ozone Mapper Profiler Suite that's aboard the Suomi NPP satellite.
IMAGE COURTESY NASA/NOAA
This image shows a cross-section of Earth's ozone layer as measured by the limb profiler, part of the Ozone Mapper Profiler Suite that's aboard the Suomi NPP satellite.

To their surprise, they found that in 2006 and 2011 the size of the holes were the same, but the total level of ozone inside them differed.

What they found next―with the help of an atmospheric model―was still more surprising. In 2006, strong winds blew more ozone over Antarctica, but there was also more ozone-depleting chlorine that year. In 2011, air masses blew in less ozone, but there was also less ozone-depleting chlorine.

So the wind effects balanced out to create a 2011 ozone hole of the same size as in 2006, but its overall amount of ozone was higher.

In 2012, the tale had another twist. Although severe ozone depletion took place at lower altitudes, strong winds brought lots of ozone to high altitudes over the Antarctic. As a result, the hole was smaller than average.

“Nobody has looked at this masking effect in detail before,” says Birgit Hassler, at NOAA’s Earth System Research Laboratory in Boulder, Colorado, who was not involved in the study. She adds, “Until now everyone assumed that one number was sufficient to explain the recovery of the ozone hole.”

Slow But Steady

The scientists still expect the ozone hole to show some signs of healing by 2025. Until then, we can expect more flip-flopping between good and bad years, the good ones bringing bringing less exposure to the sun’s harmful rays in the Southern Hemisphere—a small reprieve.

Douglass says this is “as good as can be expected. Some people would have hoped for a faster response, but we can expect a bumpy road to recovery."

Follow Olive Heffernan on Twitter.

12 comments
Whatever Trevor
Whatever Trevor

Ozone is produced in the tropics, but it's transported by the winds from the tropics to the polar region.

Abhimanyu Singh
Abhimanyu Singh

good to see that Montreal protocol has worked out so well

Chudamani Akavaram
Chudamani Akavaram

It is my beliefe that if peepal trees are planted especially in the southern parts of the world it may help recoupe the ozone layer.

Yoshimura Maroko
Yoshimura Maroko

This hole was discovered in '85. Has anyone been able to get a feel for how long it was there until then?

Paul Zottoli
Paul Zottoli

Why does the low area of ozone appear at the southern polar region and not the northern as well?  

Skip Baltar
Skip Baltar

I guess since "climate change" is crashing faster than Obamacare we need to bring up this old hoax to try to scare people huh?

Akshay Farro
Akshay Farro

what we can say is that the scientists dont really know what they are talking about till now.

Dan Carravallah
Dan Carravallah

It is very encouraging to see that if we make large scale lifestyle changes we can undo allow the atmosphere to recover.  If we keep up the fight, maybe we can make the Earth more sustainable.

Yoshimura Maroko
Yoshimura Maroko

@Paul ZottoliPossibly wind patterns or wind plus convective patterns?

It's interesting how little meaningful research is published on this.

Skip Baltar
Skip Baltar

@Dan CarravallahReally.....You do know this whole thing had to do more with DuPont's patent on R-12 running out than the ozone layer right?  Or do you still believe in global warming too?

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