For years, polls have shown that many Americans have conflated two distinct atmospheric calamities – the destruction of the planet’s stratospheric ozone layer, and global warming. A 2010 poll by Yale University found that 21 percent of respondents believe the greenhouse effect refers to the ozone layer, rather than to gases in the atmosphere that trap heat, such as carbon dioxide.
Now comes a study that helps describe the possible relationship between the two in a way that will either confuse even more people, or clarify things for anyone who devotes some time to fully digesting the new information.
According to research published in the journal Nature this week, the largest ozone “hole” on record above the Arctic opened up last winter, exposing residents of the Far North to high doses of harmful ultraviolet (UV) radiation, which can cause skin cancer and cataracts. The area of severe ozone loss extended southward from the Arctic to cover populated areas in northern Russia, Greenland and Norway.
At first glance, you might not find much to be out of the ordinary about that piece of news, since the ozone hole has been in our science textbooks for decades now. But note that I said, “Arctic,” and not “Antarctic.”
Although ozone depletion has occurred above both poles, the large and iconic ozone hole has been most acute in the Southern Hemisphere, where ideal atmospheric conditions for ozone destruction, namely extremely cold temperatures in the stratosphere, tend to exist for longer stretches of time than they do in the Arctic.
Stratospheric ozone is destroyed when atmospheric chlorine from manmade chemicals break down naturally occurring ozone molecules. The chemical reactions that accomplish this molecular homicide require extremely cold temperatures in order to take place. In a sense, you can think of the cold temperatures as an accessory to murder, if you’re like me and best understand chemistry through the prism of a Law and Order episode.
The scientific discovery that industrial chemicals were causing the loss of the ozone layer led to the enactment of the Montreal Protocol in 1989, through which countries have reduced their use of ozone-destroying chemicals such as chlorofluorocarbons (CFCs). But the long atmospheric lifetime of those ozone-killing compounds has meant that the ozone layer is going through a lengthy healing process, with continued annual occurrences of large areas of ozone loss.
Still, the observation of an Arctic ozone hole – which, while smaller than the Antarctic ozone hole, was comparable to it in terms of the amount of ozone lost – is surprising, and demonstrates that human actions can have unforeseen ripple effects for many years.
In the Arctic, the stratosphere – which is the layer of atmosphere above the troposphere, where most weather occurs – tends to be too mild for ozone depletion to progress to the same extent that it does during the Antarctic winter.
However, something odd happened during the winter of 2010-2011, according to the new study. The period of extreme cold in the upper atmosphere lasted more than a month longer than during any previously studied Arctic winter. The key reason for this was an unusually strong polar vortex, which is a cyclonic circulation of air in the upper levels of the atmosphere. Typically, the polar vortex is weaker in the Arctic than it is in the Antarctic.
“What was different about this year was that the temperatures were low enough to generate ozone-depleting forms of chlorine for a much longer period of time,” said study coauthor and University of Toronto physicist Kaley Walker in a press release.
Although the precise causes of the unusually cold stratosphere and extreme ozone depletion last winter are unclear, global warming is one factor that may be involved.
At first that might seem to be counterintuitive – as the lower atmosphere warms in response to increasing amounts of greenhouse gases in the air, the upper atmosphere cools – it’s actually rather straightforward. Greenhouse gases such as carbon dioxide trap more outgoing infrared radiation in the lower atmosphere, so less heat is allowed to pass back into the stratosphere, and the upper atmosphere cools relative to the lower levels.
“Day-to-day temperatures in the 2010-11 Arctic winter did not reach lower values than in previous cold Arctic winters,” said lead author Gloria Manney of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “The difference from previous winters is that temperatures were low enough to produce ozone-destroying forms of chlorine for a much longer time. This implies that if winter Arctic stratospheric temperatures drop just slightly in the future, for example as a result of climate change, then severe Arctic ozone loss may occur more frequently.”
The relationship between global warming in the lower atmosphere and ozone loss in the upper atmosphere is yet another reason why we need to take a precautionary approach to dealing with manmade climate change. In this case, a growing problem (global warming) may be worsening another, preexisting manmade condition (ozone loss).
For people who have long mixed up the ozone issue with climate change, perhaps learning about this relationship will help. Then again, maybe it won’t. Either way, I’m reminded of a joke by the comedian Lewis Black, who expressed his frustrations about the ozone layer thusly.
“It’s ridiculous that we still have a hole in the ozone layer. We have men, we have rockets, we have Saran Wrap - FIX IT!! And don’t come back until you do,” Black said.
If only it were that easy…
NSIDC: Arctic sea ice extent second lowest; NOAA: 8th warmest August globally
Newsflash: Climate scientists are different than the general public
Seeking answers to global warming and extreme weather questions