A Significant Ozone Hole Is Reported Over the Arctic

While the extent of the ozone depletion is considered temporary, and well below the depletion that occurs seasonally over the Antarctic, atmospheric scientists described it as a striking example of how sudden anomalies can occur as a result of human activity that occurred years ago. At its maximum extent in February, the northern ozone hole reached southward into Russia and Mongolia.

Emissions of chlorinated fluorocarbons, or CFCs, once found in aerosol sprays, and other ozone-depleting substances like the soil fumigant methyl bromide produced the first ozone hole over the Antarctic, which was identified in 1985. Emissions of those compounds were banned under the Montreal Protocol, which has been signed by 191 countries.

Since 2000, concentrations in the atmosphere have been declining, but remain about 25 percent higher than when the ozone hole was identified, said Michelle L. Santee, a planetary scientist at NASA’s Jet Propulsion Laboratory and one of the paper’s authors.

“The root cause is the residual products from the CFCs that were released throughout the 20th century,” she said. “But they are very long-lived, and it will take a few decades for them to be cleansed from the atmosphere.”

The appearance of a second ozone hole at the other end of the earth “is a reminder that human activities can have a very significant impact and often unintended consequences on the atmosphere,” she added.

In a telephone interview, Dr. Santee and a NASA laboratory colleague and co-author, Nathaniel J. Livesey, were nonetheless cautious about linking the cold temperatures in the upper atmosphere far north to the warmer weather that has been unfolding closer to the earth’s surface. That warming trend led to one of the greatest-ever reductions in the extent of Arctic sea ice this year.

Whether the cold snap in the stratosphere “is related to it being warmer than it typically is lower down is intriguing,” Dr. Livesey said, “but the connection has yet to be made.”

David Fahey, a physicist at the National Oceanic and Atmospheric Association and the author of a well-known pamphlet on the ozone layer, said the appearance of a second hole in the ozone layer underlined the unpredictability of atmospheric reactions, particularly in the far North.

“The Antarctic ozone hole is the drumbeat,” Dr. Fahey said. “We see it every year and it tells us that the stuff we did in the last two decades still matters” in terms of reducing the levels of ozone-depleting chemicals. Yet the ozone depletion recorded this year at the opposite end of the planet this year points to “the lack of predictability of what will happen in the Arctic,” he said.