The Ozone Hole Remains

A recent news flash from the European Space Agency: 2008 Ozone Hole Ranks Fifth Largest (see CNN and Science Daily coverage). Yes, after all these years, we are still worrying about the ozone hole.

Because there’s some confusion surrounding the ozone hole — some even mix it up with global warming — let’s start with a short primer.

Ozone is a molecule made up of three oxygen atoms. On the ground, ozone is a bad thing — it’s a major component of smog. But that’s not what the ozone hole has to do with. More than 90 percent of the Earth's ozone exists in the upper atmosphere, or stratosphere, where it protects the Earth’s surface from damaging ultraviolet light (read more on ozone). This is a good thing — it helps guard against things like sunburn, cataracts, and skin cancer.

The Ozone Hole Explained

Discovered in the 1980s, the ozone hole is a seasonal phenomenon. During springtime in the Southern Hemisphere, the stratosphere’s layer of ozone over the Antarctic almost entirely disappears. (For more information see this NASA video.)

This hole is an extreme example of a more modest but still worrisome decline in ozone throughout the stratosphere caused by cold temperatures combining with halogens like chlorine, fluorine, and bromine. These halogens get into the stratosphere in large part through the breakdown of synthetic compounds used as refrigerants, solvents, propellants and foaming agents (think those pesky packaging peanuts), including chlorofluorocarbons (CFCs), hydrofluorochlorocarbons (HCFCs), and halons. (See full glossary.)

Ozone Hole History

While the ozone layer has been monitored since the late 1950s, it wasn’t until 1976 that a group of British scientists unknowingly recorded the presence of a major thinning in the ozone layer above the Antarctic. Initially believing their equipment was malfunctioning, they next assumed they were recording natural variations in ozone levels, perhaps due to changing volcanic or sunspot activity (sound familiar?). It wasn’t until 1983 when a record low clearly established a downward trend that they realized something big was happening to the ozone layer. It took another two years to fit the puzzle pieces together and conclude that those halogenated compounds were the culprit.

The Global Community Takes Action

The ozone hole discovery sounded an alarm. In addition to increasing the probability of sunburn and skin cancer, a thinner ozone layer means potential disruptions to ecosystems with flora and fauna sensitive to ultraviolet light (for more dangers from ozone depletion see here and here).

Amazingly, the global community took action. Starting with the Montreal Protocol in 1987, countries agreed to phase out the more potent halogenated compounds. As a result, the concentrations of ozone-depleting compounds have been declining (see here and here [pdf]). But the stratospheric response is much slower — once those halogens get up there, they stay for a long time. And so, the ozone hole persists, with this year seeing the fifth largest, in spite of the phase-out of the culprit compounds. In fact, scientists estimate that that the ozone hole will persist until sometime around 2070.

Are There Any Connections to Global Warming?

I mentioned earlier that people sometimes confuse the ozone hole with climate change. They are not the same thing, but it turns out there is a connection. The ozone hole requires cold temperatures. A little known fact about the greenhouse effect is that while increased greenhouse gases cause warmer temperatures in the lower atmosphere, they cause upper temperatures to cool. Hence, global warming has a tendency to exacerbate the ozone hole. As a result, the recovery of the ozone layer is being slowed somewhat by our greenhouse gas pollution.

In addition, the world’s response to the ozone hole carries an important lesson. By reaching consensus on an environmental problem, the global community was able to take concerted action to address it. Could the world community do the same for global warming?

The ozone hole experience is a cautionary tale about the dangers of delaying action on environmental problems. The first warnings about CFCs and the ozone layer were raised in the early 1970s by R. Sherwood Rowland and Mario Molina (who received the Nobel Prize for their work). If the world had acted then, there would probably be no ozone hole today. But thanks to the two-decade delay in phasing out the bulk of these compounds, we will have the ozone hole for many decades to come.

Global warming has an even longer reach into the future. Some of the carbon dioxide (CO₂) emitted by the first Model Ts is still in the atmosphere causing global warming today. The CO₂ we emit today will be warming the atmosphere 100 years from now. How much longer can we afford to wait?

SIDEBAR: What If ....
Here’s a fascinating historical tidbit. Thomas Midgley, the chemical engineer who invented CFCs, was also behind the idea of adding lead to gasoline. Both turned out to be environmental disasters. Midgley (1889-1944) was clearly a clever, innovative engineer but not very lucky when it comes to the environment. For me his legacy is an apt illustration of why all educational programs should include environmental sciences. Would Midgley and his company have advanced the use of these compounds had they appreciated their environmental impacts? Doubt it.