Britain on Tuesday announced the swiftest, most ambitious climate target of any industrial economy. In so doing, it not only laid out the economic case for clean energy, but also sought to chart a very different course from its longtime ally across the pond, the United States.

Prime Minister Keir Starmer of Britain told delegates at the international climate talks in Baku, Azerbaijan, that his country would aim to reduce its emissions of planet-heating greenhouse gases by 81 percent by 2035, compared with levels in 1990.

“The race is on for the clean energy jobs of the future, the economy of the future,” he said.

The announcement at the talks, known as COP29, hinted at how Britain is trying to position itself in the world as a destination for companies that want to invest in the clean energy transition, especially at a time when President-elect Donald J. Trump has threatened to roll back the tax incentives that had recently made the United States an attractive bet for a range of clean energy companies, from battery makers to wind power firms.

Helen Clarkson, who heads the Climate Group, a nonprofit organization, and works with the private sector in advancing clean energy, said in an emailed statement that Mr. Starmer’s administration would now have to lay out a plan for companies seeking to invest. “The economic prize on offer to the U.K. is enormous,” Ms. Clarkson said.

Mr. Starmer’s left-leaning Labour Party came to office in July with a promise to accelerate the transition away from coal, oil and gas and to produce the country’s electricity mainly from renewable energy sources by 2030, a full decade ahead of the European Union.