Now the ozone layer over the Arctic is so thin that for the first time it can be called an ozone hole as well, according to new research in Nature.
The main culprit for this ozone destruction is chlorine. In itself chlorine wouldn’t be that damaging, but up in the stratosphere it reacts with nitric acid and water vapour to form a chemically active form that reacts with ozone, destroying it in the process.
Chlorine emissions have dropped significantly since the ban on CFCs, but chlorine can remain in the stratosphere for decades. Predictions show that the ozone layer won’t be at its pre-industrial health until about 40 years from now.
This forecast can be influenced by a possible strengthening of the Montreal Protocol, as there are still substantial CFC and CFC-like sources around.
Most of the damage is done at the end of polar winters when typical ice clouds are formed in the stratosphere. But this loss is usually short-lived since the ozone layer is supplemented with fresh ozone during the rest of the year.
The current state of the Arctic ozone layer however is well beyond a temporary thinning, with over 80 per cent over the ozone between 18 and 20 kilometres gone. The researchers are baffled by the incredibly large ozone loss in 2011 which was twice the size of the 2005 record.
The most probable reason for the strong decline is a prolonged cold fit in the Arctic stratosphere which lasted much longer than usual. This may partly be due to climate change, since global warming mostly takes place in the lower layers of the atmosphere, while greenhouse gases actually isolate the stratosphere, leading it to cool, increasing the chance of reaching the threshold temperature for catalytic ozone breakdown of -90 degrees Celsius.
The ozone layer in effect being the Earth’s sunscreen protects everything living from the sun’s harmful UV-B radiation. Whether the Arctic ozone layer hole has caused any human or animal health problems is as of yet unknown. If the hole turns out to be temporary a rise in skin cancer cases will probably be minimal, but of it remains it may pose a significant threat to Arctic dwelling humans and animals alike.
© Jorn van Dooren | www.bitsofscience.org