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As the effects of climate change begin to become visible, scientists, politicians, and business people are beginning to ask themselves an unthinkable question. What if our world becomes literally uninhabitable? The past five years have collectively been the hottest on record, while 2016 was the single most scorching.
Should we be looking for alternative living arrangements? And if so, where could we go? The most obvious answer is the moon, especially since US President Donald Trump has instructed NASA to return there with humans by 2024. NASA thinks that humans could live sustainably there by 2028, as long as they can find the right technology to help us survive the freezing lunar night.
Two of the world's richest men have different ideas, however. For Elon Musk, the answer lies on Mars. He has set up a company, SpaceX, which he hopes will eventually be able to take humans up to the red planet, and he says that by 2050, he plans to have a city there.
Jeff Bezos, however, thinks that we shouldn't be going to a planet at all. Drawing on the 1970s ideas of the Princeton scientist, Gerard O'Neill, the Amazon founder has suggested instead that we should look to live on spinning colonies that orbit the earth. The sun would be reflected in through a giant array of mirrors, and the weather, he says, would be like Maui on its best day all year round.
Mr Bezos believes that the best way to achieve this vision is to mine materials from the moon, where the gravitational pull is weaker and, therefore, it is cheaper and easier to launch them into space. He has set up a company, Blue Origin, which is building a moon lander which he hopes will take humans back to the moon by 2024.
Some critics say these are the idle, albeit expensive, fantasies of middle-aged men who grew up during the space race and which threaten to detract attention away from earthbound attempts to tackle climate change.
If emissions remain where they are today, then by 2050, we will have sailed past the two degrees C threshold beyond which climate scientists say the effects of climate change are likely to be catastrophic. By that point, we might have little other option.
