Environment

NASA satellite shows direct evidence of ozone hole recovery

NASA satellite shows direct ev...
A new study has found chemical evidence that the hole in the ozone layer is healing
A new study has found chemical evidence that the hole in the ozone layer is healing
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A new study has found chemical evidence that the hole in the ozone layer is healing
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A new study has found chemical evidence that the hole in the ozone layer is healing

The hole in the ozone layer was one of the most headline-hogging environmental issues of the 1980s and 90s, but an international ban on damaging chemicals has helped it recover in the 30 years since. It's long been known that the hole is shrinking, but a new study has provided greater insight into the improving health of the ozone layer by analyzing the chemicals around the hole over the last decade or so.

High up in the stratosphere, the ozone layer protects the surface of the Earth from the worst of the sun's ultraviolet light – so it was understandably alarming when scientists discovered a hole in that shield over Antarctica in the mid-80s. The culprit, it turned out, were chemical compounds called chlorofluorocarbons (CFCs), which drift into the stratosphere where UV radiation breaks them down into chlorine atoms, which then dissolve ozone molecules.

To fight back, the nations of the world rallied together to sign the Montreal Protocol in 1987, which banned the use of chemicals containing CFCs. Now decades later, the damage is slowly being undone, with scientists noticing that the ozone hole has shrunk by 4 million square km (1.5 million sq miles) overall since the year 2000.

But the size alone doesn't tell the whole story. In fact, the area of the hole fluctuates every year, peaking in size around October. That seasonal shift is due to the fact that CFCs can stay afloat in the atmosphere for up to a century, and increased UV radiation at certain times of year kickstart the ozone depletion process all over again.

The good news is that the average size of the hole has been steadily shrinking over the past few decades, but with other factors at play, scientists couldn't be completely sure that the Montreal Protocol could claim credit.

To check that the CFC ban is contributing to the recovery of the ozone layer hole, a team of researchers studied data gathered by a satellite-mounted instrument called the Microwave Limb Sounder (MLS), which measures trace gases in the atmosphere. Using MLS data gathered every winter between 2005 and 2016, the team was able to determine the daily changes in ozone levels during the entire winter season of each year – from early July to mid-September.

Sure enough, the researchers found that the rate of ozone loss decreased by 20 percent over that time period.

NASA Sees Definitive Evidence of the Montreal Protocol's Success

"This is very close to what our model predicts we should see for this amount of chlorine decline," says Susan Strahan, lead author of the study. "This gives us confidence that the decrease in ozone depletion through mid-September shown by MLS data is due to declining levels of chlorine coming from CFCs. But we're not yet seeing a clear decrease in the size of the ozone hole because that's controlled mainly by temperature after mid-September, which varies a lot from year to year."

As encouraging as the result is, we're not out of the woods yet. New CFCs aren't being pumped into the atmosphere, but the existing ones will still be around for a long time.

"CFCs have lifetimes from 50 to 100 years, so they linger in the atmosphere for a very long time," says Anne Douglass, co-author of the study. "As far as the ozone hole being gone, we're looking at 2060 or 2080. And even then there might still be a small hole."

The research was published in the journal Geophysical Research Letters.

Source: NASA

8 comments
aksdad
The complicated chemical reactions used to assign ozone hole blame on CFCs was always suspect and this report further establishes that the Montreal Protocol was based on a dubious, still unproven premise. The fact that they can measure a 20% decline in atmospheric chlorine (thanks to the Montreal Protocol) but still can’t measure any difference in ozone hole size demonstrates that the theory of a causal relationship between CFCs and ozone hole size is still just that: a theory. If there is a causal relationship, it’s apparently so insignificant that no one has been able to measure it yet even after 30 years. And the nations of the world bet billions of dollars on that. Brilliant.
Geosurfer
The title is very misleading. If you actually read the statements, it says that the ‘rate’ of ozone depletion has decreased. So, according to its own content, there is no definitive ‘recovery,’ only a slowing of the collapse.
Catweazle
"As far as the ozone hole being gone, we're looking at 2060 or 2080. And even then there might still be a small hole." There have always been holes in the ozone layer, it has been known for far longer than we have used CFSs that there were fluctuations in intensity of UV reaching the Earth's surface. Before the fashion blaming them on man there was a theory that (put simplistically) they were related to trails of H20, CH4 left behind by comets passing the Sun, heated and ionised by solar radiation and attracted to and focused on the poles by the Earth's magnetic field. Many years ago I came across a theory that used this idea to explain the anecdotal correlation of societal upheaval such as the French Revolution to cometary activity.
Pablo
CFCs have been banned in SOME countries, but are still in common use in others. I agree it was a very good idea to clean up how they're handled -no more simply venting when you're done with them, but I still believe the whole thing was a hoax to get cheap refrigerants off the market and replace them with far more expensive patented stuff.
Douglas Bennett Rogers
The half life of ozone is about six hours. Most of it goes away at night, or in winter for the polar regions. Polar stratospheric clouds, which form mainly at the south pole, act as a catalytic bed for the preferential formation of chlorine monoxide instead of ozone. Chlorinated fluorocarbon acts as a durable transport mechanism for chlorine to the stratosphere. This doesn't explain mid latitude ozone depletion, which is only inferred from chlorine monoxide concentrations.
Subtle
Ozone (O3) is the result of ultraviolet light from the Sun hitting oxygen (O2). In the polar regions, there are times when it is night all day for months. No sunshine, no UV, no ionization of O2 to O3. Thus the "Ozone Holes" which natural condition has been parlayed into comfortable livings for those who report shoddy "science" or dream up scary stuff for grants.
Fast Eddie
I feel certain that the decision to withdraw CFCs will be a good one: it stays around a long time, reason enough to get rid of it. Instead of questioning whether that was the cause of the newly-discovered ozone hole back in the 1960s, however, I want future generations to be aware of how the science was done to draw this conclusion via a "snapshot" of the atmosphere with a set of tools only a few years old. Said differently, if someone screams "Ozone Hole" in the future, they will need to have something other than CFCs to blame it on.
Craig Jennings
Some negative attitudes toward whether the Montreal Protocol has affected the ozone hole.... fair call, CFC's were pretty awesome... but so was asbestos. Living under the hole, I sure as hell am glad someone is at least trying something. Come visit NZ, it's pretty nice, just remember that the sun will hurt you, hurt you bad if you forget about the hole :)