It is sometime said that "human activity won't make a difference anyway."
That issue is still very much at the core of the debate about global warming. On one hand, scientists have presented incontravertable evidence of the earth's warming and that it is doing so at an alarming and rapidly increasing rate. It is easy to become frustrated when some folks point to the power of volcanos and assert those fantastic eruptions, in addition to other natural phenomena, surely have a far more profound impact than human activity. And though science can make a compelling argument that human activity is a cause of global warming, how does one make the case that changes in human activity will arrest the pace of change, much less reverse the damage?
Researchers investigating the impact of the global ban on chlorofluorocarbons (CFCs) enacted in 1987 in the Montreal Protocol have measured significant 'healing' of the damage to the ozone layer above Antarctica; they have documented a reduction of the size of the hole of approximately 4 million square kilometres. To put that in perspective, it's roughly the size of India. A bit less than half the size of China, or about half the size of the continetal United States. Or add Germany and France together, and multiply that by four.
Bottom line, it is a huge area of former hole. More importantly, it is a hole that has healed for one reason: we stopped using CFCs 19 years ago.