When Donald Trump announced last week that the US was pulling out of the Paris accord on climate change, other governments were rightly determined that the move neither derail the drive for lower carbon emissions nor allow the US to gain a competitive advantage.

Thoughts immediately turned to carbon border tax adjustments, a way of instituting a single international price of carbon by penalising the exports of countries with no domestic emissions pricing of their own. Like the best climate change policies, it is an elegant idea, tweaking a price and allowing the free market to respond rather than attempting a complex series of direct interventions.

However, like many good ideas, the reality is far more complex. Fiendish calculations requiring detailed data, together with potential legal impediments, unfortunately suggest a more piecemeal approach might yield better returns.