Healing the World
The closing of the ozone hole over Antarctica has positive implications for the southern hemisphere as well as global climate in general.
“The ozone layer is a thin layer of ozone in the atmosphere, 10 - 50 kilometres above the earth.”
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If ever there was a successful international agreement, it was the Montreal Protocol on Substances that Deplete the Ozone Layer. This was signed in the year 1989, by which time the ozone layer in the stratosphere was rapidly depleting and the hole over Antarctica was becoming large and damaging. The Montreal Protocol, signed by 191 countries, ensured that the production of the offending CFCs (chlorofluorocarbons) stopped in 1996. The ozone layer has started recovering quickly. The former UN secretary general Kofi Annan called it the most successful international treaty. Now it seems that its impact was even larger than envisaged by Annan or anybody else.
In a paper published in Science recently, scientists at the University of Columbia and other institutions say that the treaty could have a profound impact on the earth’s climate as well. The depletion of the ozone layer has a direct impact on human and animal health, by increasing the amount of dangerous ultraviolet radiation hitting the earth’s surface. The Columbia scientists now show that the closing of the Antarctica ozone hole will affect winds in the southern hemisphere, and hence its climate, and even the global climate. “This may be good news,” says the lead author of the study, Seok-Woo Son, a post-doctoral student at the university.
The Intergovernmental Panel on Climate Change (IPCC), which made predictions for climate change for the 21st century, did not consider the healing of the ozone hole in its assessments. In its calculations, the IPCC used a set of models that did not take into account the stratospheric ozone recovery. Son and his colleagues at Columbia University and other institutions used a different model that considered the recovery of the ozone layer. And the results were quite different.
The key issue is a type of winds called the westerlies. These winds blow in both the northern and southern hemispheres, but in opposite directions. In the southern hemisphere, the westerlies blow from the north west, and produce the Antarctic Circumpolar Current around the icy continent. This circulating ocean current is critical to maintaining the climate over Antarctica, as it keeps the warm waters away from the continent. This is why Antarctica is colder than the Arctic. This current influences the Antarctic and southern hemisphere climate in complex ways that are still not completely understood.
In the last few decades, the southern westerlies have intensified towards the pole by as much as 20 per cent. There are two reasons for this intensification. The first is the build-up of greenhouse gases in the atmosphere and the resultant warming of the earth, and the second is the depletion of the ozone layer. But we do not know how much these factors contribute individually. We do know, however, that the intensification has important consequences for the surface sea temperature, the extent of sea ice over the Antarctic, the variability of storms, location of deserts or arid regions and many other things that influence climate.
In its previous report, the IPCC had predicted that the westerlies will continue to intensify, but the rate of intensification will slow down over the next few decades. While this is expected to have several negative impacts over climate in the next five decades, we do not quite know precisely what. One of the consequences of this intensification would be the enlargement of arid zones in the southern hemisphere, mainly in Africa and Australia. Since Australia is already experiencing a serious water shortage, it will not be good news for the country.
The Columbian team, however, used a different mathematical model in their study. This model took into account the recovery of the ozone layer in general, and the complete closing of the ozone hole over Antarctica by mid century. When they ran their models, they also saw something interesting – the westerlies weakened towards the poles, in part reversing the trend in the last few decades. If this turns out to be true, the impact on climate in the southern hemisphere can be profound.
There are still many areas of this change that are not well understood, but one can certainly foresee some impacts. “I think that the expansion of the arid regions will stop,” says Son, “but we have to do much more research to know the full impact.”
One thing is clear: the thickening of the ozone layer could certainly bring some cheer.
Sources: The Telegraph (Kolkata, India)
