LONDON — Britain would bring its net production of greenhouse gases to zero by 2050 under legislation that Prime Minister Theresa May proposed on Wednesday, a move that would make it the first of the world’s major economic powers to commit to ending its contribution to global warming.
The plan does not say how the nation would reach the emissions goal or what it would cost, and future governments could change course — in fact, the proposal appears to leave the door open to backing away from the commitment if other countries do not follow Britain’s lead.
But Mrs. May’s bill, a bid to leave a legacy in her final weeks in office, sets a new bar for measuring environmental progress by the world’s major industrial powers.
“It is imperative that other major economies follow suit,” the prime minister’s office said in a statement. “For that reason, the U.K. will conduct a further assessment within five years to confirm that other countries are taking similarly ambitious action, multiplying the effect of the U.K.’s lead and ensuring that our industries do not face unfair competition.”
Some climate activists praised Mrs. May’s plan, while others said the timetable was not quick enough and the commitment not firm enough.
The finance chief in her government, Philip Hammond, has privately warned the prime minister that her proposal could cost Britain a trillion pounds, according to British news reports, and climate change skeptics have said that even that estimate could be low. But the prime minister’s office said that dire predictions like that of Mr. Hammond, the chancellor of the Exchequer, were wrong.
A law enacted in 2008 committed Britain to an 80 percent reduction in net production of greenhouse gas emissions, and it has sharply reduced emissions since then.
The government’s advisory Committee on Climate Change reported last month that total elimination was feasible. That provided the impetus for Mrs. May’s bill, which she wants Parliament to approve quickly. The idea has broad support across party lines.
The committee produced a long list of steps to reach the goal, including more energy-efficient buildings, electric vehicles, clean power production, tree planting, and capture and storage of atmospheric carbon.
Mrs. May has announced her resignation as prime minister and leader of the Conservative Party, to take effect as soon as the party chooses a new leader, which is expected next month.