In this temperature range, both poles are certain to melt, bringing an eventual sea level rise of 50 metres.

One of the most dangerous of all feedback loops will now be starting – runaway thawing of permafrost. Scientists estimate somewhere in the region of 500 billion tons of carbon are stored in the arctic ice, waiting to be released.

With the death of the Amazon and runaway carbon feedback at 3C, stabilising global temperatures at 4C may not be possible – 3C will lead inexorably to 4C, will lead inexorably to 5C.