The optimism conveyed yesterday by world leaders during the start of the COP21 negotiations has been overshadowed by news from the other side of the Atlantic. Mitch McConnell, the leader of the Republican opposition to Obama, has officially launched a boycott campaign to stop the US president’s emissions reduction plan, claiming that Obama’s green energy plan is unconstitutional. Republicans have claimed that will not support any deal the president strikes in Paris.

The majority obtained by the Republicans in the last midterm elections gives them the power to effectively block the ratification of any agreement reached at the summit. This announcement sabotages confidence in any commitments the United States may make at the summit and, given its role as the world’s second-biggest polluter, this could have serious consequences for reaching a deal.