MARRAKESH, Morocco — Diplomats at an annual United Nations global warming summit meeting here expressed shock at the election of Donald J. Trump, who has called climate change a hoax and vowed to withdraw the United States from the Paris climate change accord, worrying that Mr. Trump’s presidency could cripple a decade of climate diplomacy.

And some called for retaliation to compel American compliance. Nicolas Sarkozy, the former president of France, who is again running to lead his country, suggested imposing a carbon tariff on imports from the United States, based on the amount of carbon dioxide pollution emitted to produce various goods.

Salaheddine Mezouar, the Moroccan foreign minister, who is presiding over the Marrakesh meeting, said: “We really want the U.S., naturally. It has a huge role, a huge weight.”

Officials from the Obama administration sought to reassure the world that even if Mr. Trump rolls back the United States’ federal climate change policy, many states and electric utilities have already turned toward investing in the growing market for low-carbon energy.

The Obama administration rolled out a slew of last-minute regulations since the election of Mr. Trump, and more are planned in the coming weeks.

“You can’t keep the waves off the beach,” Ernest J. Moniz, the secretary of energy, said in an interview here, describing his message to counterparts. “We are heading to a low-carbon economy. The train has left the station.” .

And no government has said publicly that it will follow the United States away from the Paris agreement, which committed more than 190 countries to develop plans to combat climate change. Leading diplomats said they expected the pact to be followed with or without the United States.

“The agreement is not dependent on the U.S.,” said Laurence Tubiana, the French climate change envoy, who played a key role in brokering the Paris deal. “Many countries have domestic rationale for wanting to reduce their emissions.”

Still, she added, “I hope President Trump considers the laws of physics. Climate change will not stop, even if he stops implementing the rules.”

One year ago in Paris, hundreds of diplomats celebrated the new accord. President Obama hoped to make the United States a leader in combating climate change, drafting the first American climate regulations and serving as a central broker of the Paris deal.

This week’s summit meeting was intended as a low-key follow-up to agree on details for carrying out the deal. Instead, the American presidential election has taken center stage, and China, the world’s largest greenhouse gas polluter, is poised to step forward as the world’s new leader in climate diplomacy.

“It is a new world order,” Erik Solheim, head of the United Nations Environment Program, said. “Leadership on climate change policy has now gone to the developing countries, China among them.”

A new analysis of carbon dioxide emissions trends published on Monday concluded that planet-warming emissions had leveled off for the past three years in a row, chiefly because of a sharp reduction in China’s emissions.