Ozone hole as small as last in 1988

An unusually warm winter has minimized ozone depletion across the Antarctic

Extension of the ozone hole over the Antarctic in mid-September 2017. The bluer the color, the lower the ozone density. © NASA / NASA Ozone Watch / Katy Mersmann
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Short Breath: The ozone hole over the Antarctic is exceptionally small and weak this year. Measurements show that with just under 20 million square kilometers, it is as small as it has been since 1988. But the reason for the all-clear is not, as the researchers emphasize. The cause is an unusually warm winter in Antarctica, not a permanent cure for ozone depletion.

The earth's ozone layer is our most important protection against harmful UV radiation. But until the Montreal Protocol in 1987, mankind has already released so many chlorine and bromine ozone depleting substances that this protective layer is badly damaged. Even today, 40 years after the ban on these substances, an ozone hole breaks over the Antarctic every year. And even over the Arctic, the ozone layer is still thinned out.

Smaller than in the last 30 years

The question of the ozone layer in 2017 is now being researched by NASA scientists and the National Oceanic and Atmospheric Administration (NOAA). They monitor the state of the Antarctic ozone hole both by satellite and by measurements from the US South Pole station and weather balloons from there.

The result: "The Antarctic ozone hole was unusually weak this year, " says Paul Newman of NASA's Goddard Space Flight Center. The extent of the ozone hole reached nearly 20 million square kilometers in mid-September and even decreased in size until October. Thus, the ozone hole this year is the smallest since 1988, as the researchers explain.

Less thinned than usual

The ozone concentration within the ozone hole also fell less strongly in 2017 than in previous years: the scientists calculated an average of 136 Dobson units - a value that was last reached in 1988. "In the past, at certain altitudes of the stratosphere, we repeatedly measured zero values, " says Bryan Johnson of NOAA. "This year, ozone levels did not reach zero for any measurement." Display

However, the ozone layer over the South Pole is still thinned out, as the researchers emphasize. Because usually the ozone layer has values ​​between 300 and 500 Dobson units. This corresponds to a layer of pure ozone about three to five millimeters thick. Only it filters enough UV out of the sunlight to prevent major damage to humans, animals and plants.

Why the ozone hole is so small this year? NASA / GSFC

Ausrei er, no all-clear

But despite all the positive results: One reason for the all-clear is not the rather weak ozone hole this year, as the researchers emphasize. Because this is a positive spike caused by special weather conditions, but not a basic indication for a quick healing of the ozone hole. Until it closes permanently, it will take until 2050 or even 2070, so the estimates.

Instead, the cause of low ozone depletion in 2017 was an unusually warm winter over the Antarctic, as Newman and his colleagues explain. The Antarctic vortex Luft the air flow circulating around the S dpol inst was thus more unstable and warmer than usual and there were less polar stratospheric clouds. These are considered to be the environment in which the ozone-depleting reactions take place.

In addition, scientists have recently discovered that the emission of another ozone-depleting gas in the atmosphere is rapidly increasing: since the year 200, the content of dichloromethane has doubled. If this trend continues, the recovery of the ozone hole could be delayed by another 30 years, the researchers warn.

(NASA / Goddard Space Flight Center, Nov. 06, 2017 - NPO)