German Chancellor Angela Merkel is battling to prevent US President Donald Trump undermining the world leaders’ united front on climate change.
At the Paris climate deal, all world leaders spoke in favour of limiting global temperature rise to 2 degrees but that was after a massive diplomatic effort by President Barack Obama made membership of the climate club a moral imperative.
He and the French hosts created such an atmosphere that even the normally foot-dragging Russians and Saudis committed to the deal, despite their long history of slowing progress in climate negotiations behind the scenes.
They own vast fossil fuel reserves of oil and gas and fear they will stand to lose if the world shifts away from fossil fuels.
Many a UN climate conference has drawn to a semi-successful close, only for the chair to wearily announce “objection from Saudi Arabia”.
The task for Chancellor Merkel and her allies is to bind these two nervous bedfellows into the great climate alliance between the EU and China, leaving the US looking out of touch.
Ideally, from Europe’s standpoint, President Trump would recant his rejection of the Paris deal.
But that will not happen so the next least bad option is for Mr Trump to be isolated, with other nations standing together against him and in favour of stronger climate action.
President Putin wrote an article in a newspaper this week supporting the Paris deal but he and the Saudis understand that their co-operation on the matter is a huge diplomatic bargaining chip.
US solo tactic
Meanwhile the US is said to be preparing for a compromise statement that continues to reject the Paris deal but offers a promise that the US will tackle climate change on its own.
Given the president’s onslaught on his predecessor’s climate and energy policies, this pledge may ring hollow.
What is more, this is just a starting point. In Paris all world leaders acknowledged that when it came to cutting emissions to reduce the risk of dangerous climate change, they all had to do much, much more.
Environmentalists want the G20 to increase their climate commitments over this weekend. They may have to content themselves with the knowledge that the future of the planet is at least firmly on the agenda of the men and women who are running it.
Follow Roger on Twitter @rharrabin