If you’re an astronaut on the International Space Station you can see earth clearly from your window. You can even pick out some of the features, Las Vegas, for example, in all its garish splendour. And if the sky is clear you can see the Great Barrier Reef, the largest living system on the planet. Not for much longer, if the warnings are to be believed. The more than 2,500-km-long mass of coral is going through a serious convulsion with massive bleaching in the last couple of seasons due