Ozone Hole Won't Heal Until 2070
The banning of ozone-depleting chemicals hasn't yet caused detectable improvements in the Antarctic ozone hole.
SAN FRANCISCO - The banning of ozone-depleting chemicals hasn't yet caused detectable improvements in the Antarctic ozone hole, new research suggests.
Instead, changes in the South Pole's ozone hole from year-to-year are likely the result of natural variations in wind patterns, researchers said here Wednesday (Dec. 11) in a press conference at the annual meeting of the American Geophysical Union.
"Ozone is produced in the tropics, but it's transported by the winds from the tropics to the polar region," said Anne Douglass, a scientist with the Aura project at NASA's Goddard Space Flight Center in Greenbelt, Md. That transport "varies a little bit from year to year."
The findings suggest that measuring the total size of the ozone hole says little about ozone depletion, and that it's misleading to use the hole's extent alone to measure environmental progress. In fact, people won't be able to see the true impact of reducing ozone-munching chemicals in the atmosphere until around 2025, Douglass and her colleagues said. And, they added, the hole won't be completely healed until 2070. [Top 10 Ways to Destroy Earth]
Big hole Ozone is a molecule made up of three oxygen atoms, and the ozone layer, which stretches from heights of 12 to 19 miles (20 to 30 kilometers) above the Earth's surface, protects life on Earth by shielding it from ultraviolet (UV) radiation.
Until the 1990s, the widespread use of chlorofluorocarbons (CFCs) for refrigerants and aerosols created an ozone hole in the Earth's stratosphere (the second layer of the atmosphere from Earth's surface) over Antarctica. CFCs deplete ozone, because they can bind to oxygen molecules in several chemical reactions, breaking ozone down into regular oxygen molecules. Without the ozone there, harmful UV rays can reach the planet's surface, posing a threat to humans and Earth's other life forms.
An international agreement called the Montreal Protocol, first signed in 1987, gradually phased out the use of CFCs, and the amount of the chemicals in the atmosphere has slowly declined since.
Missing piece The classic way of measuring the hole is by measuring the total area that contains less than 220 Dobson units of ozone. But the ozone layer extends vertically throughout the stratosphere, so using just one measure is like "looking at a flat table," Douglass said.
That traditional measure may miss what's really going on in the stratosphere. For instance, in 2012, the ozone hole shrank to record lows, even though the level of CFCs in the atmosphere hadn't declined dramatically, said study co-author Natalya Kramarova, also at NASA Goddard. Paradoxically, the ozone hole in 2011 was about as big as it was in 2006, even though CFCs should have declined in those years due to the phasing out of their use.
So Kramarova took a closer look at data gathered by the Suomi National Polar-orbiting Partnership satellite, which showed ozone levels with altitude. The small size of the ozone hole in 2012 was a result of weather bringing in more ozone at higher levels of the stratosphere than usual to Antarctica, masking the depletion at lower levels. [101 Stunning Images of Earth from Orbit]
In a second study, researchers used the Aura satellite's Microwave Limb Sounder to peek inside the ozone hole through chemicals such as nitrous oxide, which inversely varies with levels of chlorine, a byproduct of CFCs, in the Earth's atmosphere.
The researchers found that in 2011, chlorine levels were lower despite the ozone hole's big size. Using a computer model, they showed that weather conditions would have lowered the amount of ozone over Antarctica anyways, and that the big hole was a result of winds from the tropics carrying less ozone to the area than in the years before.
"This is a meteorological effect, it has nothing to do with chemistry," said study co-author Susan Strahan, a NASA Goddard atmospheric chemist.
CFCs are incredibly stable molecules that must travel high into the stratosphere before breaking down, so though the phasing out of CFCs is working, the impact of the Montreal Protocol won't be noticeable in the ozone layer until about 2025, Kramarova said.
Until then, annual measures of peak ozone hole size should be taken with a grain of salt, the researchers said.
The hole won't likely be fully healed until about 2070, Kramarova said.
Of course, for people in the Southern latitudes, UV exposure is only dependent on the size of the hole, so it doesn't matter whether weather patterns or CFCs are responsible for its extent.
Original article on LiveScience.
Images: One-of-a-Kind Places on Earth Images: Mission Flies Above Antarctica's Icy Wilderness 50 Interesting Facts About The Earth Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
The area of the ozone hole, such as in October 2013 (above), is one way to view the ozone hole from year to year. However, the classic metrics have limitations, NASA scientists say.
Jason Ahrns, a graduate student at the University of Alaska-Fairbanks, goes sprite-chasing at night during electrical storms. Here he captures column-shaped red sprites over Red Willow County, Nebraska, on Aug. 12, 2013.
A “jellyfish” sprite photographed over Republic County, Kansas, on August 3, 2013. "I have very good low light eyesight, and I've watched tons of sprites in real time on the context cameras so I know exactly what and where to look. I was watching intently out the window while I snapped these shots, and the camera caught a sprite that I didn't see," writes Ahrns in his blog: http://musubk.blogspot.fr/2013/08/sprites-2013-update-4.html
Like flames from a butane lighter, three blue jets (slightly blurred due to the motion of the aircraft) appear above the lightning-lit clouds in this photo taken over Republic County, Kansas, on August 3, 2013. Ahrns describes this picture as the "the cream of the crop," due to the difficult nature of capturing blue jets. "Since jets tend to hug the top of the clouds it's understandable that they're more difficult for a ground observer to see/photograph, so it makes sense that being up in a sprite-chasing aircraft would give me a serious advantage," he writes.
"Unlike sprites, blue jets aren’t directly triggered by lightning, but seem to be somehow related to the presence of hail storms," reports the Smithsonian: http://blogs.smithsonianmag.com/artscience/2013/08/scientists-capture-rare-photographs-of-red-lightning/.
Red sprite over Canadian County, Oklahoma, on August 6, 2013. "I was also able to see quite a few jets with my naked eyes! That's a first for me, and I'm always excited to see a new sky phenomenon for myself. I still haven't been able to see a sprite naked-eye, and it impresses me just how difficult that actually is," Ahrns writes.
Ahrns' Nikon D7000 on a flexible tripod points out the window of the sprite-chasing aircraft, a Gulfstream V with the National Center for Atmospheric Research. "I butted the camera up against the window glass and put my weight on it to get rid of most of the wobbles and light leaks, but the motion of the aircraft itself still showed up, especially when we hit a patch of turbulence (we are, you know, flying right next to a thunderstorm)," he writes.
Ahrns' high-speed video set-up next to the window of the Gulfstream V.
Sprites over Red Willow County, Nebraska, photographed on Aug. 12, 2013.
Sprites over Red Willow County, Nebraska, photographed on Aug. 12, 2013.