NASA said the depletion of the ozone layer above the Arctic reached a record level in March.

Citing satellite observations, the government agency said the ozone levels reached 205 Dobson units, compared to a usual level above the Arctic at approximately 240 Dobson units. A Dobson unit is defined as the measurement of the total amount of ozone in the atmosphere above a particular point on the Earth's surface and is 1 millimeter thick, according to NASA.

“This year’s low Arctic ozone happens about once per decade,” said Paul Newman, chief scientist for Earth Sciences at NASA's Goddard Space Flight Center in a statement. “For the overall health of the ozone layer, this is concerning since Arctic ozone levels are typically high during March and April.”

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The ozone layer is approximately 7 to 25 miles above the Earth's surface and acts as a "sunscreen" for the planet, according to NASA. It keeps out harmful ultraviolet radiation from the sun that has been linked to skin cancer, cataracts, immune system suppression and can also cause damage to plants.

NASA added the depletion of the Arctic ozone in March was likely due to "unusually weak upper atmospheric 'wave' events from December through March." These events are similar to weather systems that are routinely seen in the lower atmosphere, but occur in the upper atmosphere "much bigger in scale."

These waves usually come from the lower atmosphere and "disrupt" or alter the winds that swirl around the Arctic. When that happens, the ozone is brought with them from other parts of the stratosphere.

“Think of it like having a red-paint dollop, low ozone over the North Pole, in a white bucket of paint,” Newman added. “The waves stir the white paint, higher amounts of ozone in the mid-latitudes, with the red paint or low ozone contained by the strong jet stream circling around the pole.”

NASA added that the wave events were weak in December 2019 and the period from January to March 2020, preventing the ozone from other parts of the atmosphere from replenishing over the Arctic.

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“We don’t know what caused the wave dynamics to be weak this year,” Newman explained. “But we do know that if we hadn’t stopped putting chlorofluorocarbons into the atmosphere because of the Montreal Protocol, the Arctic depletion this year would have been much worse.”

In March, a study was published that said the ozone layer is continuing to heal and could recover completely, thanks to the global actions from the 1987 Montreal Protocol.

Chlorofluorocarbons were banned completely by the Montreal Protocol, enacted in 1987 after scientists disturbingly found a hole in the ozone over Antarctica and Australia in 1985. It was enacted by the United Nations Environment Program.

Former U.N. Secretary-General Kofi Annan called it "[p]erhaps the single most successful international agreement to date," with the ozone continuing to recover each year.

A total of 197 countries, including the U.S. under former President Ronald Reagan, are signatories of the Montreal Protocol.

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