The Antarctic ozone hole in the southern hemisphere is known for its annual fluctuations. This year it has a counterpart.
An ozone hole has developed over the Arctic, a rare occurrence that scientists say is the largest such atmospheric opening ever recorded over the northernmost regions of the planet.
Persistent cold temperatures in the polar region and unusually calm ozone dynamics, according to Paul Newman, chief scientist for geosciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, have led to a record breakdown of the earth̵
“It’s an unusual event,” said Newman. “There is some arctic ozone depletion every year, but it will be more extreme in 2020 than in most years.”
The earth’s ozone layer acts as a protective skin and protects the surface of the planet from the harmful ultraviolet radiation from the sun. But over the past century, man-made chemicals known as chlorofluorocarbons have devoured ozone and partially thinned it – and left it gaping.
This year, so-called polar stratospheric clouds formed in the Arctic at icy temperatures at high altitudes. Scientists have long known that these types of clouds play a key role in the destruction of Earth’s ozone because they provide a surface high in the atmosphere where chemical reactions that release harmful forms of chlorine can take place.
“It’s the unusual temperatures this year that led to unusual levels of polar stratospheric clouds that led to unusual ozone depletion,” said Newman, who runs NASA’s Ozone Watch, an online portal that tracks the health of the planet’s ozone layer .
Another factor that has affected the formation of the Arctic ozone hole is an observed lack of ozone mixture in the stratosphere, he added. In a normal year, weather systems can stir up large atmospheric waves that rise from the lower atmosphere through higher altitudes and mix ozone in the stratosphere. But this year, Newman said, was strangely quiet.
“We have seen winters like this, so the real question is: why is it so dynamically calm in the Arctic?” he said.
Newman said that scientists don’t yet know why atmospheric mixing is slowing, but he said that this is likely a key factor in ozone depletion across the Arctic.
Earlier ozone holes above the North Pole were discovered in 2011 and 1997, but this year’s degradation – an area slightly larger than Virginia – is the largest in NASA’s 41-year record, according to Newman.
The arctic ozone hole is expected to heal and will likely disappear in the next month or so.
“Our forecasts indicate that temperatures in the polar vortex are beginning to rise,” said Vincent-Henri Peuch, director of the European Union’s Copernicus Atmosphere Monitoring Service, which is investigating the phenomenon, in a statement. “This means that ozone depletion will slow down and eventually stop because polar air mixes with ozone-rich air from lower latitudes.”
The depletion event is not expected to raise significant health concerns, but Newman said any break in the ozone layer is worrying.
“The sun is not very high in the Arctic right now, so it doesn’t make much difference, but if these low levels persisted, you would see ever higher UV levels,” he said. “Low ozone leads to more UV radiation, so that’s not a good situation.”
In 1987, 197 countries signed an international treaty known as the Montreal Protocol to protect the ozone layer by phasing out ozone-depleting chemicals such as chlorofluorocarbons. Without this pioneering multilateral agreement, Newman said, the situation in the Arctic would likely be much worse.
And although the Arctic has a record low in ozone, the situation in the northern hemisphere is fading compared to the ozone hole in Antarctica, which is far larger and much more volatile.
The ozone hole in Antarctica usually peaks in September and October, before recovering in December and growing again in the spring. Last year, the Antarctic ozone hole was the smallest since its discovery in 1985, but the largest opening in 2006 averaged 10.3 million square miles – larger than the entire North American continent.
“If the current situation in the Arctic were above Antarctica in September or October, we would say that the ozone hole has disappeared – that is the big difference we are talking about,” said Newman. “This is unusual for the Arctic, but not at all comparable to the ozone hole in the Antarctic.”