The most talked about hole in the ozone layer is the hole in Antarctica, but sometimes the protective ozone over the Arctic is also destroyed for the last time and on record in 2020. Why do fewer such events occur in the northern hemisphere? The ozone layer is a natural shield in the stratosphere that protects life on Earth from harmful levels of ultraviolet radiation and is “monitored” by ground-based observation stations and satellites such as the Sentinel-5P of the European Copernicus program. .
Between July/August and October/November each year in Antarctica, a hole forms in the ozone layer (which then closes), but not in the Arctic. At these latitudes, the last ones were tracked in the spring of 1997, 2011, and 2020 and have always been much smaller than those in the southern hemisphere.
The maximum width of the 2020 Arctic hole was calculated to be about one million square kilometers, Diego Loyola of the German Aerospace Center (DLR) tells Efe very little if you take into account that Antarctica reached a maximum of about 24.8 million square kilometers in the same year.
Loyola is one of the researchers who studied two years ago thanks to data from the Sentinel-5P TROPOMI instrument. “Strange” hole drilled over the North Pole. As published in the journal Atmospheric Chemistry and Physics, the observations offered record low values for ozone.
“Since March 14 and over the course of five weeks, the ozone columns over the Arctic have been reduced to what would normally be considered ‘ozone hole levels,’ i.e. less than 220 Dobson units,” the Ecuadorian scientist summarizes.
“Ingredients” for a hole in the ozone layer
Ozone is a gas in the air we breathe and can be good or bad.Javier García-Serrano, from the Meteorology group at the University of Barcelona, reminds Efe: “bad” is at ground level and relates to pollutants from cars or factories, and “good” protects us from the sun’s ultraviolet rays. sun.
Both Loyola and García-Serrano emphasize that: A number of conditions must coincide for a hole to form in the ozone layer.: Extremely low temperatures in the stratosphere (especially below -80 degrees Celsius), sunlight, wind fields, and substances such as chlorofluorocarbons (CFCs).
The temperature in the stratosphere, which is colder in Antarctica, is therefore directly related to ozone depletion. Because polar stratospheric clouds, which play an important role in the chemical destruction of ozone, only form below -78 degrees Celsius, defines the World Meteorological Organization (WMO).
These clouds contain ice crystals that can render non-reactive compounds reactive by rapidly destroying ozone in the presence of sunlight, which triggers chemical reactions.
Additionally, much of the ozone depletion occurs within the so-called polar vortex (more intense in Antarctica), a region in the stratosphere where very strong circular winds blow and isolate the air mass inside, keeping it at a very low temperature. .
As temperatures in the stratosphere begin to rise, ozone depletion slows, the polar vortex weakens and eventually deteriorates and levels return to normal.
effect on weather
The WMO states that the destruction of the ozone layer in these years would have been much greater had it not been for the Montreal Protocol.
Ozone-depleting substances (like CFCs and halons) were once used in refrigerators or fire extinguishers and have been phased out thanks to the Protocol, but they remain in the atmosphere for decades and their concentrations are still high.
Whether changes in the ozone layer have consequences for the climate is an old science debate; In the Antarctic example, there have been studies pointing to this for years.
For example, in 2011 Science published research by scientists at Columbia University that found: The hole in the ozone layer affects the atmospheric circulation up to the equator in the southern hemisphere. and this causes an increase in precipitation in the subtropics.
More recently, last July, Nature Another published focus Arctic: Every time the ozone layer gets thinner, weather anomalies have subsequently been observed across the Northern Hemisphere.
Springs in central and northern Europe, Russia and especially Siberia were extremely hot and dry.
Researchers led by the Federal Polytechnic University of Zurich ran simulations in which ozone depletion was integrated into two climate models and concluded: The weather anomalies observed in 2011 and 2020 were mainly due to the thinning of the ozone layer over the Arctic.
Both García-Serrano and Loyola find these results interesting and plausible, but they add to the discussion more than lay the groundwork.
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