Slap on the sunscreen: Arctic ozone could hit all-time low this spring

They may look pretty but these polar stratospheric clouds, photographed Feb. 2 over Scotland by atmospheric scientist Hugh Pumphrey of the University of Edinburgh’s School of GeoSciences, are the precursors to ozone destruction in the stratosphere. (PHOTO BY HUGH PUMPHREY)

Inuit and other Arctic dwellers who head out on the land in March may want to apply a little sunscreen first.

Scientists who study the earth’s atmosphere have noticed a significant decrease in ozone levels over the Arctic recently and, with the sun’s return in spring, they predict that ozone hole will get a lot bigger.

“At certain altitudes, we’ve already seen about 25 per cent of the ozone being destroyed. That’s the amount we’re sure of,” said Gloria Manney, an expert in stratospheric dynamics and transport at Northwest Research Associates in New Mexico.

“The big question is: what happens next? Because since these reactions depend on sunlight, as you can imagine, as we go into the spring, toward the equinox… these reactions will get much more rapid.”

The earth’s ozone layer — located about 20 to 30 kilometres above the surface of earth in a layer of the atmosphere called the lower stratosphere — absorbs most of the sun’s ultraviolet (UV) rays and protects life forms on earth, including humans, from harmful radiation.

Produced annually high above the tropics during the summer months, ozone is annually circulated and distributed throughout the stratosphere so every year, ozone is replenished.

The Montreal Protocol, an international treaty which went into force in 1989, bound nations to phase out human made ozone-depleting chemicals.

But ozone is still being destroyed in other ways and this year, it seems to be happening on a grand scale.

Scientists are predicting ozone destruction over the Arctic this spring will exceed the highest recorded depletion, which took place in 2011. That year, 80 per cent of the ozone over the Arctic was destroyed.

The science behind this phenomenon is interesting, albeit complicated, and we can expect it to happen more frequently as the earth’s climate warms, said Manney. Here’s why.

There is a fixed amount of heat radiating from the sun.

As greenhouse gases, such as carbon dioxide and methane, collect in the earth’s atmosphere, these gases trap more heat closer to the earth, warming the climate.

But as a result of that entrapment, less heat leaks out into the atmosphere’s higher altitudes in the stratosphere.

And so the stratosphere is getting colder. When that happens, water vapour and nitric acid condense more frequently at high altitudes to form what are called polar stratospheric clouds — beautifully colourful, but foreboding in nature.

When a harmless form of chlorine gas, which is naturally present in the stratosphere, comes into contact with those unusual clouds, the chlorine is transformed into its “active” form.

And chlorine, in its active form, destroys ozone.

Scientists who study stratospheric meteorology, such as Manney, have noted the stratosphere is colder than normal and has been that way since mid-December.

Satellite-based Instruments which measure gases in the stratosphere have also shown that the amount of “inert” or harmless chlorine in the stratosphere is diminishing while active or harmful chlorine is fast increasing.

The final ingredient in this equation is sunlight, Manney said. Sunlight is what causes active chlorine to destroy ozone and right now, there’s little sunlight in the Arctic.

But the polar vortex — that large mass of low pressure and cold air that contains this chemical soup and naturally swirls around the poles — is unusually large in the Arctic this year. Parts of it have expanded down into southern regions where there is sunlight in winter.

In fact, even with the limited amount of sunlight penetrating the polar vortex this year, there is already more ozone depletion than at this time during the record-breaking year of 2011.

And so scientists predict most of the ozone over the Arctic could be destroyed this spring.

However, it’s only a prediction, Manney says. Stratospheric weather is extremely variable from year to year anyway so it’s difficult to know what will happen and how quickly the stratosphere might warm up and slow down this process.

“The question is, do the temperatures stay low long enough? Does the vortex stay intact long enough and, as temperatures rise, how long does it take for the chlorine to turn back into the safe form?” she said.

“All those are open questions because we can’t really forecast in detail the temperatures more than a week to 10 days in advance.”