The Ozone Hole Opens Up Again. It’s Still Not The Same as Climate Change
Ozone levels over the Arctic as detected by satellite on March 16. Credit: NOAA
The sun is rising over the Arctic after months of darkness, and when that happens, ozone watchers get wary. That's because a combination of stratospheric ice crystals, chlorine and sunlight can trigger a chemical reaction that destroys ozone molecules — and while ozone is a pollutant at ground level, its presence in the stratosphere protects us from potentially harmful ultraviolet rays from the Sun.
This effect was identified back in the 1970s, at about the same time as climate scientists were beginning to worry seriously about greenhouse gases and climate change — which may be one reason why people still confuse the two. But climate change comes mostly from chemicals that already occur naturally, such as carbon dioxide (CO2) and methane, whose warming effect is actually essential to life on Earth; the problem is that humans have been pushing these gases beyond their natural levels. Nevertheless, considerable confusion between climate change and ozone depletion persists. For example, a 2010 poll by Yale University found that a full 21 percent of a sample of American adults thought the greenhouse effect refers to the ozone layer, rather than to gases in the atmosphere that trap heat, such as CO2.
Ozone depletion, by contrast, comes from a different set of chemicals called chlorofluorocarbons, or CFCs, which are purely artificial substances, used in spray cans, refrigerators and air conditioners. In the mid-1970s, researchers Sherwood Rowland and Mario Molina noted that CFCs could in theory waft up to the stratosphere, where the chlorine they contain could destroy ozone (Rowland, Molina and Paul Crutzen, who also worked on ozone depletion, won the 1995 Nobel prize for their prediction). In the mid-1980s, scientists with the British Antarctic Survey detected just that sort of destruction in the frigid skies over Antarctica. That in turn led to the 1987 Montral Protocol, which banned CFCs and other ozone-depleting chemicals.
But it takes a while (and that's an understatement) for the chemicals that have already been released to break down. So while most CFCs have been off the market for more than 20 years, a new hole opens in Antarctica every spring (in the Southern Hemisphere, that means September). It happens in the Arctic as well, but since the temperatures aren't reliably as cold around the North Pole, and the air currents aren't always right, significant ozone holes up there don't happen every year. "It's more like every six or seven years," says National Oceanic and Atmospheric Administration (NOAA) chemist Bryan Johnson. Johnson is in charge of NOAA's Ozonesonde Group, which sends balloons up into the stratosphere to sample what's going on in the atmosphere, and this, he says, may be one of those years.
In fact, he says, "it's happening now." Ozonesondes and satellites are already recording a drop in ozone around the edges of the Arctic, where the sun peeks above the horizon earliest. If temperatures in the upper atmosphere stay low and the winds keep blowing in the right way, it could easily keep going. "The potential is there," says Johnson. "If conditions persist into the end of April, we could see a hole comparable to what happens in Antarctica."
Whether or not that will happen, however, is anybody's guess. "If you look out more than seven days in advance," says Johnson, "it's like the weather — it's really hard to predict."
What Johnson does predict is that ozone holes should gradually vanish as the remaining CFCs and other ozone-eating chemicals break down. "I'm still confident about recovery," he says. "We won't see this effect 50 years from now. Until then, it'll go up and down from year to year, depending on conditions, but chlorine levels are going down."