Actually today's (lengthy) Info-Nugget comes not from Bill Bryson, like previous days, but from Tim Flannery, an Australian expert on fossils, mammals and climate. I'm just finishing off his book The Weather Makers, having read most of it earlier in the year. The bit that caught my eye was when Flannery was telling the story of how CFCs damaged the ozone layer. Things could easily have been so much worse if the world had chosen to use something called BFCs instead.

CFCs were developed in the late Twenties to be the 'refrigerant' inside fridges: the liquid that carries the heat away from your yoghurt and milk. Only much later did researchers work out that CFCs released into the atmosphere were burning a hole in Earth's ozone layer.

In case you don't recall, normal oxygen in the air consists of two oxygen atoms (O2) joined together. But it's possible to stick three oxygen atoms together to form ozone (O3), though it's not very stable. Ozone gets formed in our upper atmosphere as cosmic rays smash into regular O2 and split it into individual oxygen atoms. These lone atoms are super reactive and each can attach to a normal O2 molecule to make ozone. While ozone is toxic to breathe, it's a handy thing to have floating around in the upper atmosphere because it absorbs ultra-violet (UV) light. Even a small amount of it cuts out a lot of the really nasty UV that reaches Earth.

When CFCs reach the upper atmosphere they too can be struck by cosmic rays and split into pieces, just like oxygen. The first 'C' in CFC stands for 'chloro' and when CFCs are broken up, chlorine is released. One chlorine atom can have a big effect. It bounces around reacting with ozone, turning it back into ordinary oxygen, and then moving on. Despite the fact that escaped manmade CFCs made up a very small fraction of the atmosphere, they still did a lot of damage. First a hole in the ozone layer developed over the South Pole and then another, smaller one formed over the North Pole. The holes formed there because chlorine reacts with the most ozone when it's cold. Each year the holes got bigger.

The effect was an increase in skin cancer rates and a gradual killing off of little organisms that couldn't stand the UV radiation. Some of those organisms formed important links in major food chains. Fortunately once researchers saw what was happening they raised the alarm. Flannery notes that no one took much notice for a while, despite the danger (and those with a vested interest in CFCs launched PR campaigns defending them) but once ordinary people started seeing satellite pictures on the news with big gaps in our UV shield shimmering in front of their eyes politicians came under pressure to do something. The Montreal Protocol was the result: an agreement to get rid of CFCs, and it looks like it will stand a very good chance of eliminating the ozone holes in another few years time.

But the detail of the story which caught my eye was very early on when Flannery talks about an alternative to CFCs called BFCs. They do roughly the same job, but use bromine instead of chlorine. They're marginally more expensive and luckily for all of us it was CFCs that caught on instead. Bromine is forty-five times more damaging to ozone than chlorine. Instead of finding a hole over the poles, in a world that used BFCs, they'd have found the ozone layer in tatters. Food chains all over the world would have collapsed, skin cancer and cataract rates would have shot up, animals would have died, crops would have failed, and it's possible that the results would have been bad enough to trigger a major collapse of the global economy. If bromine had been a whisker cheaper than chlorine instead of a whisker more expensive it could all have been very different.