Thursday, June 11, 2015

Ozone Hole Continues to Increase - Projected At Least Until 2040

Antarctic ozone hole as it appeared in 2006, highlighted in purple and blue. It marked the largest hole area yet observed at more than 273 million square kilometers. (From EOS Transactions, Vol. 96, No. 10, p.28).

It seems strange that many believe the problem of the growing ozone hole over Antarctica is now solved, and no longer a problem. Nothing could be further from the truth and new research reveals the extent of the problem. In truth, atmospheric scientists have observed as the ozone hole has formed every spring from the Southern Hemisphere.

The origin is no mystery and the erosion of the ozone layer,  caused by enormous inputs of CFCs or chloro-flourocarbons, has been known for at least 40 years. Each CFC molecule, as the late Carl Sagan pointed out in a 1979 article, is capable of eliminating tens of thousands of ozone molecules (each composed of 3 oxygen atoms) that form the protective barrier against harsh UV or ultraviolet radiation. The type that causes more skin cancers and cataracts. Humans caused this massive ozone erosion, which reached up to 70% of the ozone layer over the South Pole by late 1979- through the use of chemicals including: aerosols, solvents and refrigerants.

When these CFCs reach the stratosphere, the chlorine atoms are liberated by ultraviolet radiation from the Sun, which incept the erosion of the ozone. The peril arising from this erosion reached the point that by 1987, the nations of the world agreed to the "Montreal Protocol" to halt the harmful emission of these CFCs.  As a result the hole quit growing by the mid-1990s.

That's the good news. The bad news is that recovery of the protective ozone shield has been slow because many of the ozone depleting chemicals can last in the atmosphere up to 100 years - a lot of time to keep causing damage, erosion.

Despite the fact CFCs are no longer being emitted in any vast quantities, atmospheric scientists don't forecast the ozone hole to disappear until at least 2070.  They calculate that the gradual destruction of CFCs already in the atmosphere causes chlorine to decline each year by roughly 20 parts per trillion or 0.5%. However, as reported in EOS Transactions, Vol. 96, No. 10, p.28, Earth-orbiting satellites indicate that the natural variability of chlorine levels over Antarctica is up to ten times larger than the expected annual decline. 

In fact, in some years the chlorine levels have declined as much as 200 parts per trillion or 5% but in other years it increased by 150 ppt.  According to Strahan et al (Journal Of Geophysical Research - Atmospheres, 2014) it will take a decade of exclusive chlorine declines to be certain that the Montreal Protocol has caused the ozone hole to shrink.

Currently, it is low temperatures in the Antarctic that play the largest role in determining the size of the ozone hole. For example, in 2006, the combination of very low temperatures and high chlorine levels produced the largest ozone hole ever. It won't be until 2040, according to the authors, that we'll be able to expect the chlorine levels to have fallen enough that the ozone hole will he smaller than it is today, even given a very cold year.

Given these natural fluctuation issues, we are left with years of monitoring both temperature and chlorine levels before it can definitively be said that the declining trends can be attributed to the Montreal Protocol. Yes, the Protocol has evidently worked, but the inordinate lifetimes of the CFCs has made full removal extremely difficult, and requiring an extended time frame. 

This is also a cautionary tale for those who deny climate change-global warming, since an analogous situation applies. As reported in EOS Transactions of the American Geophysical Union (Vol. 91, No. 30, 27 July, 2010),  CO2 is so long-lived in the atmosphere (~ 100 years for each molecule from the time deposited) and so much has been injected by humans, "it could effectively lock the Earth and future generations into warming not just for decades or centuries but literally for thousands of years."

Something to think about!

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