The price of EU carbon credits, which have been the world's best-performing energy commodity in the past year, is set to double again by 2021, according to a top sector analyst who quit Barclays for a climate-change think tank this month.

The cost of these credits could go even higher if EU governments follow through on pledges they made at the Paris climate accords in 2015, he said, reaching a level that would doom the continent's coal energy industry entirely.