After frustrating talks in Bonn with an American delegation in limbo, UN climate negotiators are pinning their hopes for the Paris Agreement's future on diplomatic arm-twisting at the highest level.
On the campaign trail, now-president Donald Trump vowed to "cancel" the 196-nation pact to rein in global warming by curbing emissions from burning oil, coal and gas.
He has not yet executed his threat, but Trump has made it clear where he stands.
His secretary of state was a CEO of oil giant ExxonMobil, and the Environmental Protection Agency head an anti-climate litigator. Trump has moved to slash EPA funding, and to loosen restrictions on coal-fired power plants and vehicle emissions.
Now the man who has called climate change a "hoax" perpetrated by China, is scheduled to rub shoulders with some of the world's most influential leaders in a duo of high-stakes huddles.
The first is a May 26-27 summit in Sicily of the G7 rich nations, followed on July 7-8 by a meeting in Hamburg of the G20 major economies, of which the G7 also forms part.
Key members of both groupings have already called on Trump to stay the climate course.
"If Donald Trump is unclear on the lethal implications of his muddled climate policy then it’s up to the other leaders of the G7 to ensure he is aware of just how damaging his actions can be," said Mohamed Adow, an analyst with Christian Aid, which advocates for poor country interests at the UN climate forum.
"They must make a strong case for action when they meet."
At the G7 meeting, Trump will talk with his peers from Germany, Canada, France, Britain, Italy and Japan.
The leaders of Germany and Canada, as well as France's new president Emmanuel Macron, are viewed as champions of the climate cause.
But this type of multilateral discussion involves much diplomatic give-and-take on a wide range of political and economic issues of national interest. There are some doubts there will be time or space for a strong focus on global warming.
The White House has said Trump will not announce his decision on the Paris Agreement until after the G7.
Jochen Flasbarth, Germany's state secretary of the environment, said in Bonn this week that climate change was "one of the issues of highest priority" for his country's presidency of the G20.
"We work very hard together with many other friends in the world to convince the US that staying in the Paris Agreement is the right way to go," he said.
There are fears in the UN climate forum that an American withdrawal may prompt others to follow suit, or simply undermine the collective will, crafted over two decades of tough negotiations, to ramp up climate action over time.
Also under threat is US climate funding.
Trump is unlikely to honour an outstanding $2billion pledged under his predecessor to the Green Climate Fund, or America's contribution to the budget of the UN climate secretariat (UNFCCC).
The uncertainty cast a long shadow over technical negotiations, hosted by the UNFCCC in Bonn from May 8 to 18, on a nuts-and-bolts "rule book" to implement the deal.
Some delegates said it might be better to let the US break ranks than let it undermine the negotiations from the inside.
"It may be the case that he (Trump) is listening to the ExxonMobils and wanting to actually think through how to use that seat at the table," commented Adow.
Others say the rest of the world should better "ride out" Trump's presidency and wait for the next administration to pursue America's commitments under the deal.
But this comes with uncertainty.
"After four years will there be a new president who is favouring" climate action? "Maybe not," said Qimin Chai of China's National Center for Climate Change Strategy and International Cooperation.
For Adow, China will be key in cranking up the pressure in the coming weeks.
China's Xi Jinping was instrumental, alongside Barack Obama, in pushing the Paris deal through.
On Sunday, Beijing hosted a meeting on international trade, attended by the leaders of such countries as Russia, Argentina, Belarus, Indonesia, the Philippines, Switzerland and Turkey.
In what is considered a message of climate solidarity against Trump, the leaders' closing statement encouraged "all parties which have ratified it to fully implement the Paris Agreement."
Other key opportunities for building diplomatic pressure, say observers, include the so-called Petersberg Climate Dialogue in Berlin on May 22 and 23, which will draw participants from 35 countries, and an EU-China business summit in Brussels on June 2.
Trump is also due to meet Pope Francis, a strong proponent of global action against climate change, at the Vatican on May 24.