The suspicion must be that what we are seeing is a co-ordinated movement by two of the countries that have most vehemently opposed tough international action to restrict emissions over the last few years - perhaps as a buffer in case the EU starts looking at other trade-related climate measures, such as border adjustments, more seriously.

BBC: EU's aviation charge is a drop for China's airlines

Today it has about four times greater resources than what was available to it when that action was taken in 2009, so we think that is a very important buffer for the international community.

WHITEHOUSE: Press Briefing