A few weeks ago, the European Space Agency announced the latest good news for one of the most successful international pollution regulation programs to date. According to measurements by Europe’s Met Op weather satellite, in 2012 the hole in the ozone layer was smaller than it had been for a decade. Longer-term observations also show that the ozone layer has been strengthening, subsequent to international agreements limiting ozone-depleting substances, especially CFCs.
The ozone layer, at 12 to 19 miles above the surface, blocks incoming ultraviolet (UV) light from the sun. UV light damages living organisms – we are aware of its effects on our skin in the form of sunburns and skin cancer. It is nasty stuff; the bare 3% of UV radiation that slips through the atmosphere is capable of giving us lobster-red skin. Without the ozone layer blocking a great deal of the UV radiation headed Earth’s way, life would likely be confined to the deep oceans.
Since the 1980s, scientists have observed a hole in this critical layer, recurring every year from September through November over Antarctica. The ozone layer is affected by a combination of atmospheric chemistry and weather, especially wind and temperature. In the Antarctic, the absence of land around Antarctica allows the development of very strong circumpolar winds, since there is nothing in their way to slow them down. These winds create a vortex that traps air over Antarctica, leading to extremely low temperatures. In these conditions, human-made chlorofluorocarbons – CFCs – are able to rapidly deplete ozone, leading to the well-known ozone hole.
We do not observe an ozone hole over the Arctic because the landmasses in the northern hemisphere prevent such strong winds from developing. The temperatures remain higher, and CFCs are unable to wreck such havoc on the ozone layer. As a result, the southern hemisphere feels the brunt of the impact from CFCs and other ozone depleting substances.
The Montreal Protocol, which came into force in 1989, is the international treaty responsible for the phasing out of ozone-depleting substances and thus for the remarkable recovery we are observing in the ozone layer. It is a remarkable example of international cooperation; it and the Vienna Convention for the Protection of the Ozone Layer are the most widely ratified treaties in UN history. This broad acceptance of the the need for an industrial shift to protect our atmosphere and ourselves has led to an astounding 98% reduction of global production of ozone-damaging substances.
The foresight and prompt action by the international community has averted a great deal of suffering. Without the Montreal Protocol, almost two-thirds of the ozone layer would have been depleted by 2065. This reduction would lead to a tripling in the strength of UV rays, which would have had negative impacts well beyond health problems. UV light also damages plants, and so a reduction in crop yields would likely also have occurred.
Finally, the Montreal Protocol (inadvertently) contributed to the fight against climate change, as ozone-depleting substances are also greenhouse gases. The ozone layer has other complex interactions with temperature, circulation, greenhouse gases and climate that are not entirely understood. However, scientists do expect that the recovery of the ozone hole to counteract the effects of climate change – although these effects occur only in the southern hemisphere summer.
CFCs and related substances were so widely useful because of their low reactivity in normal conditions; this asset has become a problem, as their low reactivity means that they will linger in the atmosphere for many decades. For this reason, although the Montreal Protocol governed the near-complete phase-out of CFCs by 2010, a full recovery of the ozone hole is not expected until mid-century. Although this seems like a long recovery time, it is significantly shorter than it would have been without the strong and swift response of the international community to the warning of scientific studies.