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WASHINGTON — The Trump administration formally notified the United Nations on Monday that it would withdraw the United States from the Paris Agreement on climate change, leaving global climate diplomats to plot a way forward without the cooperation of the world’s largest economy.

The action, which came on the first day possible under the accord’s complex rules on withdrawal, begins a yearlong countdown to the United States exit and a concerted effort to preserve the Paris Agreement, under which nearly 200 nations have pledged to cut greenhouse emissions and to help poor countries cope with the worst effects of an already warming planet.

Secretary of State Mike Pompeo announced the notification on Twitter and issued a statement saying the accord would impose intolerable burdens on the American economy.

“The U.S. approach incorporates the reality of the global energy mix and uses all energy sources and technologies cleanly and efficiently, including fossils fuels, nuclear energy, and renewable energy,” Mr. Pompeo said.