While Guterres did not mention the Trump administration in his speech, but responding to a question from the audience later, he said the United Nations believes "it would be important for the U.S. not to leave the Paris agreement" and even if Trump withdraws, "it's very important for the USA society as a whole - the cities, the states, the companies, the businesses - to remain engaged" with the climate agreement.
But there may be "caveats in the language" the US President uses to announce the move - leaving open the possibility that the decision might not be final, they added.
And yet even Musk, the CEO of Tesla and SpaceX who has been pushing the world toward a future of renewable energy, was not able to sway the Trump administration to remain in the Paris Climate Agreement.
What is the Paris climate accord?
President Trump is nearing a decision on whether to formally withdraw the US from the Paris climate agreement - a landmark deal in which almost every country volunteered to curb its greenhouse gas emissions in an effort to limit global warming.
Aims of the Paris agreement include keeping the average global increase in temperature to below 2 degrees Celsius above pre-industrial levels and mitigating against the impacts of climate change.
Leaving the deal would fulfill a central campaign pledge, but would anger global allies who spent years in hard negotiations that produced an accord to reduce carbon emissions.
"We are committed to working with you to create jobs and boost USA competitiveness, and we believe this can be best achieved by remaining in the Paris Agreement", read the letter. It also "sends a combative signal to the rest of the world that America doesn't prioritize climate change and threatens to unravel the ambition of the entire deal".
Some have questioned whether the Paris Agreement could survive the US's withdrawal. The U.S., which took the lead in negotiating the deal, signed onto the agreement in April 2016, along with China, the European Union and 171 other nations.
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The US president has previously vowed to abandon the deal reached during the tenure of his predecessor Barack Obama.
Trump has said that he will soon announce his decision on whether America will leave the Paris Agreement or stick to the commitments it made under the Obama administration.
Trump claimed before taking office that climate change was a "hoax" created by the Chinese to hurt the US economy, an assertion that stands in defiance of broad scientific consensus.
"If we lag, the noose tightens", said Princeton University climate scientist Michael Oppenheimer, co-editor of the peer-reviewed journal Climatic Change.
The decision will put the United States in league with Syria and Nicaragua as the world's only non-participants in the Paris Climate Agreement.
Italian Prime Minister Paolo Gentiloni, who chaired the meeting, said the other six "won't change our position on climate change one millimeter". Critics of the accord say the limits on emissions place an onerous and disproportionate burden on American businesses (although other business leaders disagree).
Economically, the Paris agreement is a job-killing disaster for the U.S.as well.
The process of the US withdrawing from the agreement could take at least three years, and scientists warn such a decision could have dire consequences for the planet.