25 April

I’d like to do a few posts on climate change. The whole topic is infected with political slogans, but the real knowledge is fascinating. Probably the greatest slogan is that ‘the climate always changes’. People arguing that this is a natural process, so nothing to worry about. It is true that the Earth has had periods of much greater global warming than right now, during the time of the dinosaurs for example. CO2 levels then were about twice what they are now, over 800ppm. The Earth has two main climate phases. One is called Greenhouse Earth, or Hothouse Earth, which was what the dinosaurs experienced. No continental ice, even the poles had forests. An absolute proliferation of life, though also large low-oxygen zones in the seas (you need ice at the poles in particular to make ocean waters circulate). The other is Ice Ages, where there is continental ice. We’re in an Ice Age right now. The amount of ice can vary widely during an Ice Age, and right now it’s diminishing rapidly. The danger of climate change scientists try to warn us about isn’t that we might end up with a Greenhouse Earth, like the dinosaurs. Life can flourish in those conditions. It’s the speed of the transition that is lethal. Huge numbers of humans for example live in coastal cities, which will be underwater. And dinosaurs had millions of years to evolve to cope with that extra heat, but with fossil fuel burning we’re bringing about these changes in only a few centuries. It’s the SPEED of the change that threatens human civilisation itself.