The hole in the ozone layer over Antarctica last week reached a moderately large size for the third year in a row — larger than all of North America — but experts say it’s still shrinking overall, despite recent upticks due to cold weather. at high altitude.
The hole in the ozone layer reached its largest size of more than 10 square miles (26.4 million square kilometers) on Oct. 5, the largest it has been since 2015, according to NASA. The scientists noted that because there have been cooler-than-normal temperatures in the southern polar regions at an altitude of 12 to 20 kilometers (7 to 12 miles) where the hole is located, conditions are ripe for chemicals chlorinated that react with ozone molecules and destroy them.
“The general trend is for improvement. This year it’s gotten a little bit worse because it’s been a little bit colder,” said Paul Newman, chief terrestrial scientist at NASA’s Goddard Space Flight Center who monitors ozone depletion. “All the data indicates that the ozone is recovering.”
Just looking at the maximum size of the hole in the ozone layer, especially in October, can be misleading, said Susan Solomon, an MIT ozone gas scientist.
“Ozone depletion starts later and it takes longer for the hole to reach its maximum size, and the holes are usually shallower” in September, which is the key month to watch for ozone recovery, not October, Solomon said Thursday in an email.
Chlorinated and bromide chemicals high in the atmosphere eat away at Earth’s protective ozone layer. Low temperatures create clouds that release these chemicals, Newman explained. The colder, the more clouds and therefore the bigger the hole in the ozone layer.
Climate change science says that heat-trapping carbon from burning coal, oil, and natural gas causes the Earth’s surface to warm, but the upper stratosphere, above the trapped heat, cools Newman said. However, the hole in the ozone layer is slightly below the region thought to be cooling due to climate change, he noted. Other scientists and investigations do relate the cooling of the area with global warming.
“The fact that the stratosphere is showing signs of cooling due to climate change is worrying,” said Martyn Chipperfield, an atmospheric scientist at the University of Leeds. What is worrying is that climate change and attempts to reduce the ozone hole are intertwined.
Seth Borenstein is on Twitter at: @borenbears
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