The price of carbon in the EU's emissions trading scheme hit a 10-year high, reaching €18 per tonne on Aug. 13, up about 200% from the year-ago levels, The Guardian reported.

"It will already be cutting into coal profits," said Phil MacDonald, the head of communications at Sandbag, a group that monitors the carbon market.

For years, the cost has hovered around €5 per tonne, which had not provided enough of a jolt to prompt companies to lower emissions, the report said. Sandrine Ferrand, a market analyst at Engie Global Markets, said the added cost would be significant for coal, but the incentive to switch fuels would be hampered by the increase in gas and oil prices, the report said.

The upsurge in carbon pricing is due to, in part, the European Commission reforms to cut the supply of carbon permits from January as well as the heatwave affecting large parts of Europe, The Guardian said, adding that its continued climb would affect Germany's newly-formed "coal exit commission," which is set to release a plan in 2018.

Chris Piabiatek, a carbon trader at Vertis Environmental Finance, which expects a tonne of carbon to cost just under €19 in 2019, said a no-deal Brexit that involves the U.K. stepping out of the carbon market would be "super bearish" for carbon prices, The Guardian said.