There is a photograph, taken ten years ago in Paris, that today seems like something of a relic.
In it, dozens of men and women line up in dark suits, in front of an enormous sign that reads COP21 Paris.
Right in the middle the UK's then-Prime Minister, David Cameron, grins widely, as he stands beside the future King Charles III, just in front of China’s Xi Jinping. Far off to the right is the then US President Barack Obama, deep in conversation with someone who is cut off from the frame - because there were so many leaders lining up that day that it was difficult for the photographer to capture them all at once.







