The WMO today reports rapid and record-breaking thinning of the ozone layer over the Arctic region over the course of this winter and early spring – with now 40 percent of it gone. Unusually low temperatures in the stratosphere, even cold records, are at fault – creating conditions whereby ice crystals form in so called polar stratospheric clouds.
These special ice clouds then set the stage for some undesirable atmospheric chemistry. On the onset of spring, when the Sun comes up over the polar night but the air is still winter-cold, over the Arctic all conditions can suddenly be met to set the catalytic ozone breakdown reaction in motion: sunlight, moist, CFKs [yes, they’re still around] and temperatures of -90ºC (or colder). That critical temperature is so low it is actually quite rare, even by ‘stratospheric standards,’ even over the Arctic.
Oddly, such low temperatures in the stratosphere could be a consequence of elevated levels of greenhouse gases.
We’re in bed with just one part of the atmosphere
The ozone layer (simply a part of the stratosphere with a relatively high concentration of uv-blocking ozone molecules) is situated at an altitude of 13 to 40 kilometres above the Earth’s surface. That is well above almost all of the heat-absorbing greenhouse gases – these stay in the lowest few kilometres of the atmosphere, the troposphere.
We also live in the troposphere – right among all these molecules of CO2 and methane – and the same goes for all the ecosystems around us, up to the very peak of Mount Everest. That is why, to us, the rise in the concentration of these greenhouse gases manifests itself as global warming, a rise in the average temperatures over the Earth’s surface.
The ozone layer however can be seen as ‘lying on the wrong side of the blankets’. As the absorbing layer of greenhouse gases becomes thicker the stratosphere and ozone layer become isolated among, well, the nothingness of space, where everything is very, very cold.
IPCC AR4 [pages 702 and 703] states the GHG-associated tropospheric warming and the stratospheric cooling can be found in both models and [good old weather balloon] observations. The IPCC actually cites measurements of stratospheric cooling as evidence against the hypothesis that global warming would be caused by increased solar activity, as in such case the entire atmosphere would have to show a warming trend, including the stratosphere.
UNEP Earthwatch warns the ozone crisis isn’t over yet. We did manage to mitigate its source, production and emission of CFCs, to an important extent. But there will be lots of the hazardous gases in the atmosphere for decades to come. And when stratospheric temperatures would keep declining there is still a clear possibility of a seasonal ozone hole over the poles. And especially in case of the Arctic these holes could be uncomfortably close to populated areas.
There is however one clever thing we can do. We did manage to find a solution to the CFC problem. But there is still work to be done on these other two nasty categories of fluorocarbons: HCFCs and HFCs. If we find a way to better tackle these through an extension of the Montreal Protocol, we could be doing something unfriendly to two birds simultaneously.
The same gases that deplete the ozone layer happen to also be potent greenhouse gases themselves. Per molecule they actually exert a warming effect that is thousands of times as strong as that of CO2 [that remains the most important contributor to climate change, simply because we emit such enormous amounts of it].
Extra measures to clamp down on the remainder of CFCs and on the HCFCs and HFCs could not only help avoid ozone layer breakdown, they could also proof an additional tool for the UN’s efforts to combat climate change. It is estimated such ambitious ozone policy could (ideally, over several decades) equate to 122 gigatonnes of CO2 emission reductions. To place such numbers in perspective: that would rejuvenate the atmosphere a tad less than 4 years. On the optimistic side: that’s still 365 times as good as the economic recession we hear so much about in the news.
© Rolf Schuttenhelm | www.bitsofscience.org