After Donald Trump announced that he was pulling the US out of the Paris Agreement on climate change at the beginning of June, political scientist Daniel Drezner tweeted: “This was the day that Angela Merkel became leader of the free world.” Hosting the G20 in Hamburg earlier this month, and recognising the reality of a deeply interconnected world that we must shape together, she emphasised that Germany chose the square knot as the logo for this G20 meeting “because it refers to the maritime heritage of Hamburg”, a great trading city, and because “it is particularly effective and strong when you pull on it with greater force”.

If we try to imagine Germany replacing the US as global agenda-setter, diplomatic catalyst, and military enforcer — a role that Mr Trump rejects — a deeper truth becomes immediately apparent. Ms Merkel, or any other national leader, for that matter, could steer the G20 only by embracing a different form of leadership: a process of empowering groups to take and implement collective responsibility for tackling specific problems.

This kind of collective leadership is called “system leadership” because participants understand how they are tied together in an interconnected system and must work together on all dimensions of a complicated problem.