The Arctic Ozone Sieve: More Global Weirding?

This is the ozone hole like you've never seen it before.

Is the ozone hole related to climate change or the "greenhouse effect"? In a word, no.

What about Global Weirding (Thomas Friedman's phrase for increasingly extreme weather conditions)? Possibly not.

First, some background: {my emphasis shown in bold}

The Antarctic Ozone Hole was discovered by the British Antarctic Survey from data obtained with a ground-based instrument from a measuring station at Halley Bay, Antarctica, in the 1981-1983 period. They reported the October ozone loss in 1985. Satellite measurements then confirmed that the springtime ozone loss was a continent-wide feature.

Research conducted during the National Ozone Expeditions to the U.S. McMurdo Station in 1986 and 1987, and NASA stratospheric aircraft flights into the Antarctic region from Chile in 1987 showed conclusively that the ozone loss was related to halogen (chlorine)-catalyzed chemical destruction which takes place following spring sunrise in the Antarctic polar region. The chlorine is derived from manmade chlorofluorocarbons (CFCs) which have migrated to the stratosphere and have been broken down by solar ultraviolet light, freeing chlorine atoms.

The ozone hole is formed each year in the Southern Hemisphere spring (September-November) when there is a sharp decline (currently up to 60%) in the total ozone over most of Antarctica. During the cold dark Antarctic winter, stratospheric ice clouds (PSCs, polar stratospheric clouds) form when temperatures drop below -78C. These clouds are responsible for chemical changes that promote production of chemically active chlorine and bromine. When sunlight returns to the Antarctic in the Southern Hemisphere spring, this chlorine and bromine activation leads to rapid ozone loss, which then results in the Antarctic ozone hole. Although some ozone depletion also occurs in the Arctic during the Northern Hemisphere spring (March-May), wintertime temperatures in the Arctic stratosphere are not persistently low for as many weeks which results in less ozone depletion.

Owing to regulations on the production and use of certain ozone-destroying chlorinated compounds, which went into effect in January 1996, the atmospheric concentration of some of these man-made substances has begun to decline. Chlorine/bromine should reach maximum levels in the stratosphere in the first few years of the 21st century, and ozone concentrations should correspondingly be at their minimum levels during that time period. It is anticipated that the recovery of the Antarctic Ozone Hole can then begin. But because of the slow rate of healing, it is expected that the beginning of this recovery will not be conclusively detected for a decade or more, and that complete recovery of the Antarctic ozone layer will not occur until the year 2050 or later. The exact date of recovery will depend on the effectiveness of present and future regulations on the emission of CFCs and their replacements. It will also depend on climate change in the intervening years, such as long-term cooling in the stratosphere, which could exacerbate ozone loss and prolong recovery of the ozone layer.

Although increasing greenhouse gas concentrations in the atmosphere may result in warmer surface temperatures, colder temperatures are expected to occur in the stratosphere. In fact, temperatures in the lower stratosphere, as measured by NOAA's Microwave Sounding Unit, have cooled during the past 22-years, the length of the satellite record. Colder stratospheric temperatures can enhance ozone loss through their affect on the formation of polar stratospheric clouds which in turn promote chlorine-caused ozone destruction.

To clarify the common misunderstanding that the arctic ozone hole is somehow related to climate change (see below), I asked my colleague Dr. Feng Qi, a faculty member in our Department of Geology and Meteorology:

{Note: I believe that a more appropriate term is "ozone sieve" rather than a hole, because the NOAA data indicates a significant decrease in concentration of ozone, not the absence of ozone.}

...it is right that Ozone depletion has nothing to do with Climate change. The former is something happening in an upper layer of the atmosphere (Stratosphere) while the later is related to something happening in the lower layer (troposphere). Ozone depletion was caused by the manmade CFCs. Although it has been banned for a number of years now, such compounds degrade very slowly in the environment so they keep reacting with ozone in the stratosphere. An ozone hole is not really an empty hole (0 concentration of ozone). It is just very low concentration of. Since ozone helps filter out harmful UV radiation, ozone depletion is obviously an environmental hazard (to humans). Climate change mostly relates to the increased level of CO2 in the troposphere, which blocks the infrared energy emitted by the earth surface, prevent such from escaping, therefore increase the temperature in the lower atmosphere. Therefore it is not related to the ozone matter above.

From Michael D. Lemonick's recent article on this topic, the observed "ozone sieve" is going to around for decades:

... 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.

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."