In September came some signs of movement. Two of the three announced plans to make sharp cuts, though many details remain unknown.
In mid-September, the European Union president, Ursula von der Leyen, proposed more aggressive emissions cut by the 27-member bloc in the next decade. Her new target, which is yet to be approved by the European Parliament: trim emissions by 55 percent by 2030, compared to 1990 levels. The European Union has already committed, by law, to become carbon neutral by 2050, which means reducing carbon dioxide emissions and offsetting those that remain by figuring out how to offset their impact.
A week later, President Xi Jinping of China announced in an address to the United Nations that his country, too, would speed up its climate plans, with a target to be carbon neutral before 2060.
That leaves the United States. And it makes the results of the November elections crucial to global efforts to avert catastrophic climate change.
Mr. Trump rejects climate science, has pulled the United States out of the Paris accord, an international agreement designed to slow down temperature rise and avert the worst climate impacts, and rolled back a series of environmental regulations. His challenger, Mr. Biden, has promised to bring the United States back into the Paris Agreement and proposed to invest $2 trillion to address climate change by, among other things, spurring the development of clean energy infrastructure.
By the time the United Nations convenes a meeting on Dec. 12 for world leaders to update their climate commitments under the Paris Agreement, the United States will be out of the accord or on its way back in.
“Climate disruption is daily news,” the United Nations secretary general, António Guterres, said Thursday, “from devastating wildfires to record floods.”