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The IPCC commissioned four different models of what might happen to the world economy, society and technology in the 21st century and what each would mean for the climate, given a certain assumption about the atmosphere’s “sensitivity” to carbon dioxide. Three of the models show a moderate, slow and mild warming, the hottest of which leaves the planet just 2 degrees Centigrade warmer than today in 2081-2100. The coolest comes out just 0.8 degrees warmer.

Now two degrees is the threshold at which warming starts to turn dangerous, according to the scientific consensus. That is to say, in three of the four scenarios considered by the IPCC, by the time my children’s children are elderly, the earth will still not have experienced any harmful warming, let alone catastrophe.

But what about the fourth scenario? This is known as RCP8.5, and it produces 3.5 degrees of warming in 2081-2100. Curious to know what assumptions lay behind this model, I decided to look up the original papers describing the creation of this scenario. Frankly, I was gobsmacked. It is a world that is very, very implausible.

For a start, this is a world of “continuously increasing global population” so that there are 12 billion on the planet. This is more than a billion more than the United Nations expects, and flies in the face of the fact that the world population growth rate has been falling for 50 years and is on course to reach zero – i.e., stable population – in around 2070. More people mean more emissions.