Do Ozone Holes Form Over the Arctic? | Ecology

Get the Answer of: Do Ozone Holes Form Over the Arctic?

(a) The strato­spheric temperatures are seldom below—80°C due to frequent exchange of air masses with the mid-latitudes;

(b) The Arctic air vortex usually dissipates in late winter before sunlight returns to initiate the ozone destruction.

The differences between the two regions result in part from the larger land mass in the northern hemisphere, which causes more activity in the atmosphere.

Nevertheless, analysis of satellite data reveals that the loss of ozone in the northern hemisphere is now proceeding faster than previously thought. In 1989, NASA’s Airborne Arctic Stratospheric Ex­pedition, the first comprehensive research expe­dition to explore the Arctic region, found that the Arctic stratosphere in winter has almost as much chlorine monoxide as is found in Antarctica, the same destructive chlorine that causes the Antarc­tic ozone hole.

While no Arctic ozone losses com­parable with those in the Antarctic have occurred, localised Arctic ozone losses have been observed in winter concurrent with observation of elevated levels of reactive chlorine, made available through man-made emissions of CFCs. Ozone losses have increased greatly in the 1990s in the Arctic and in late 1997 were the great­est ever observed, according to measurements by NASA satellites.

The rate of loss in mid-latitudes has reached 8% per decade in late winter and spring, and sig­nificant loss is now encroaching on the growing season. This compared with the yearly-averaged global mean decreased in the amount of ozone of about 3% in the last decade.

An ozone hole in the Arctic is expected to grow larger over the coming decades as a result of man-made greenhouse gas emissions which may cause climate change, before recovering after 2020. Loss of ozone in the Arctic by 2020 could be about double what would occur without greenhouse gases.

Though greenhouse gases cause atmo­spheric warming at the Earth’s surface, they cool the stratosphere by trapping more heat below, in the troposphere.

Since ozone chemistry is very sensitive to temperature, particularly at -80°C when Polar Stratospheric Clouds can form, this stratospheric cooling may result in more ozone depletion in the Arctic. Temperatures are slightly warmer in the Arctic than the Antarctic during their respective winter and spring seasons, with the re­sult that ozone loss in the northern hemisphere has been lower than that in the southern hemi­sphere.

But the Arctic stratosphere has gradually cooled over the last decade, resulting in the in­creased ozone loss. Computer models predict that temperature and wind changes induced by green­house gas emissions may allow a stronger and longer-lasting atmospheric vortex to form above the Arctic, as in the Antarctic causing an increase in ozone depletion.