NEW BRIGHTON, N.Z. It was a cloudy day at the beach when I got my first New Zealand sunburn, butterflied across my chest between the straps of my halter-top and the collar of my sweater. Having been sunburnt only twice before (while dozing under a full sun), I’d disregarded warnings, neglected sunscreen and would now pay the toll in embarrassment.

 

New Zealanders, however, take sun safety seriously. The country’s high latitude intensifies the summer sun, and fragments of the Antarctic ozone hole sometimes drift overhead, allowing extra doses of cancer-inducing ultraviolet rays to reach Earth’s surface. As a result, New Zealand’s skin cancer rate is among the highest in the world. Skin cancers represent 80 percent of cancer diagnoses in the country, with close to 70,000 new cases diagnosed each year.

 

Therefore, Kiwis adhere to the “Slip, Slop, Slap” regimen of public-service announcement fame: Slip on long-sleeves, slop on sunscreen and slap on a hat. Beyond that, sit tight while the ozone hole closes.

 

It will take decades for the ozone layer, the stratospheric band of ultraviolet-absorbing O₃ molecules, to fully recover from the chemical insults piled upon it by humans during the 20^th century, when we added billions of tons of chlorofluorocarbons and other halogenated gases to the stratosphere. There, solar radiation pops off free-radical chlorine (and other pesky, reactive halogen) atoms, which skitter about, colliding with ozone and breaking it into diatomic oxygen (O₂), which lacks the absorptive properties of its allotrope.

 

In the process, the guilty chlorine radicals regenerate, allowing the cycle to continue indefinitely until, at last, two chlorine radicals collide with one another by chance, locking themselves into Cl₂ gas and ending the cycle. In a low-density atmosphere with few of these radicals, this takes a long time: A single chlorine radical can destroy tens of thousands of ozone molecules within its reactive lifetime.

 

So even though the Montreal Protocol (signed by 164 countries to regulate the production of ozone-harming compounds) has been in force since 1989, it has taken more than two decades to see convincing results.

 

Fortunately, the most severe effects on the ozone layer are seasonal and localized.  Ozone destruction is enhanced in cold air masses — those usually found over the poles, where polar stratospheric clouds form. During the Antarctic springtime, cold air masses held stationary by the polar vortex are exposed to their first sunlight, and ozone levels may be depleted by up to 80 percent. Since the frozen continent isn’t exactly a human population center, we only worry about this “Ozone Hole” when parts of it extend over Australasia.

 

Last year, scientists reported significant decreases in the size of the Antarctic Ozone Hole. Previous analyses were hampered by interannual variation: the extent and intensity of ozone depletion varies as a function of air currents, temperature and, of course, the concentration of man-made chemicals.

 

A shrinking ozone hole is real cause for celebration. In recent years, the international effort to eliminate ozone-damaging chemicals has become the benchmark against which comparably weak attempts to curb carbon dioxide emissions are measured. It’s good to see that, when countries put faith in science, their actions were ultimately rewarded.

 

Despite last year’s auspicious austral news, one troubling report came from the Arctic: a multinational scientific team reported the largest amount of ozone destruction ever recorded in the North. Arguably, an Arctic Ozone Hole was formed for the very first time. In their article describing the late-March ozone minimum, the authors remarked on the unusually cold winter and strong polar vortex that precipitated the phenomenon, raising an interesting point.

 

Anthropogenic climate change warms the planet but cools the stratosphere, increasing ozone destruction. This counterintuitive phenomenon is further complicated by the knowledge that ozone, by absorbing ultraviolet light in the stratosphere, warms the stratosphere.

 

In the Antarctic, this means less stratospheric circulation; the cold air stays put above the frozen continent, insulating it and slowing the effects of climate change.

 

So in an oddly backward way, patching the ozone hole may accelerate Antarctic warming.

 

But before we start mass-producing CFC-filled air conditioners, let’s think for a moment about adaptation. Success stems from flexibility. Yes, we have a tremendous ability to modify — and even control — our environment. Yet as we become set in our ways, we are left behind. How long can we afford to ignore the exhaustion of our fossil fuel resources? How long before we pay more attention to the accelerating shifts of our swiftly tilting planet?

 

So slap on some sunscreen, climb to higher ground and hold on. It’s going to be an interesting ride.

 

Holly welcomes comments, tubes of SPF-45 and spray-on tan at hollyvm “at” stanford “dot” edu.