A USA withdrawal would seriously undermine global efforts to limit carbon emissions, which the vast majority of experts say are changing the climate in risky ways.
The key mission of the May 8-18 meeting is to start drafting "rules" for putting the agreement into action: what information must countries include in their emissions updates, for example, and how must they report? "But, obviously, the speculation coming out of Washington is now at the top of our minds", said Thoriq Ibrahim, minister of environment and energy for the Maldives and chair of the Alliance of Small Island States.
The letter was reported by The Washington Examiner. The pact helped solidify a global consensus about addressing climate change that environmental groups worry may be undermined if the world's largest economy withdraws.
The final diplomatic push, led by former US President Barack Obama and China's Presdent Xi Jinping, among others, resulted in 195 countries making climate change pledges.
Of course, none of this will be the news out of Bonn if Trump announces a Paris exit in the middle of the talks.
The deal was sealed at the 21st so-called "Conference of Parties" (COP 21) in the French capital in December 2015, after years of haggling. At issue is whether staying in the accord could legally oblige President Donald Trump to preserve carbon-cutting policies that he is moving to jettison.
But this year the gathering has been politically charged by Trump's imminent decision.
There has been a chorus of appeals from United States and foreign business leaders, politicians and non-governmental organisations (NGOs) for Washington not to abandon the agreement - including from the prime minister of Fiji, which will preside over the next round of high-level talks in November.
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The board's advisers are appointed for three-year terms, which are typically renewed even under a new administration. Freire said there was no specific plan to seek out more industry appointees for the Board of Scientific Counselors.
Widely hailed as the last chance to stave off worst-case-scenario global warming, the Paris pact was savaged by Mr Trump during his presidential campaign.
"The question of whether this creates a hard backdrop for the negotiations is clearly a "yes", said Paula Caballero, who heads the climate programme at the Washington-based World Resources Institute (WRI).
"Mr. Trump's potential decision to leave the Paris Agreement would be poison for global climate efforts and leave investors in a limbo of uncertainty", said Pelle Pedersen, signatory and head of responsible investment at the Danish pension fund PKA, according to the Financial Times. To the contrary, the USA will be sending a "much smaller" delegation than it has in years past, the official said.
The Obama administration pledged in 2015 to reduce USA carbon output by 26-28% by 2025, but the lynchpin of achieving that goal - closing coal-fired power plants - is under review by the Trump administration and is expected to be scaled back if not eliminated outright.
"We urge all nations to stand by their commitments to the [Paris] Agreement and to put in place policy measures to achieve their nationally-determined contributions (NDCs) with the utmost urgency", the letter reads.
Some are floating the idea that the United States should be allowed to change or even reduce its commitments to cut carbon as long as it stays in the deal.
Supporters of the deal have argued that countries can legally curb their emission reduction commitments under the treaty and are urging the U.S. to remain a signatory to the deal.
Even if Trump does opt to leave, stipulations in the deal mean the United States would likely have to remain until the end of 2020 - when the next U.S. presidential election is scheduled to occur.