Remember the hole in the ozone? (TIME magazine does.) Thanks largely to the unchecked use of chemicals like chlorofluorocarbons (CFCs) and halons in the postwar era, the ozone layer thinned dramatically—especially over the Arctic and Antarctic poles. That was bad news for life on Earth because the ozone layer blocks harmful blocks UV-B radiation. Thin the ozone layer, and you increase the amount of UV rays that reach the Earth’s surface—and our skin. (Indeed, since 1990 the risk of getting melanoma has more than doubled in part due to the loss of stratospheric ozone.) But thanks to the Montreal Protocol—the 1987 international treaty that phased out ozone-depleting chemicals—the ozone layer has been on the mend for the past two decades.
But healing takes time, and the ozone layer is far from fixed. Today the World Meteorological Organization (WMO) warned that ozone over the Arctic had suffered record loss over this spring—in large part because of unusually cold temperatures in the Arctic stratosphere this winter, along with the continued impact of ozone-depleting chemicals. From the WMO:
Observations from the ground and from balloons over the Arctic region as well as from satellites show that the Arctic region has suffered an ozone column loss of about 40% from the beginning of the winter to late March. The highest ozone loss previously recorded was about 30% over the entire winter.
In Antarctica the so-called ozone hole is an annually recurring winter/spring phenomenon due to the existence of extremely low temperatures in the stratosphere. In the Arctic the meteorological conditions vary much more from one year to the next and the temperatures are always warmer than over Antarctica. Hence, some Arctic winters experience almost no ozone loss, whereas cold stratospheric temperatures in the Arctic lasting beyond the polar night can occasionally lead to substantial ozone loss.
Even though this Arctic winter was warmer than average at ground level, it was colder in the stratosphere than for a normal Arctic winter.
It looks like this:
That doesn’t meant the Montreal Protocol was a failure, though. Just like carbon dioxide, ozone-depleting chemicals have a long life in the atmosphere, so the CFCs released by your old refrigerator in the early 1980s, before the Protocol went into effect, might still be up there, eating away at the ozone. “The arctic stratosphere continues to be vulnerable to ozone destruction caused by ozone-depleting substances linked to human activities,” organization Secretary-General Michel Jarraud told reporters.
The Arctic isn’t heavily populated, so ozone-depletion in the far North won’t pose a major threat to human health—but winds can move the hole around. In fact, the WMO warned late last month that some ozone-depleting areas might have reached Greenland and northern Scandinavia. Still, the ozone hole is slowly healing itself, and the phasing out of CFCs and the like remains one of the most important success stories in environmental—and international legal—history. The WMO estimates that ozone layer outside the polar areas will recover to their pre-1980s levels by 2030-40, the Antarctic by 2045-2060, and the Arctic a couple of decades later. So the world may warm and the seas may rise—but at least we’ll have managed to restore that thin blue chemical layer that makes life on this planet possible.