The U.S. President Joe Biden on Thursday doubled country's ambitions on slashing greenhouse gas emissions, leading Japan and Canada at a summit in making new commitments that bring the world closer to limiting the worst climate change.

Putting the United States back at the forefront on climate, Biden told a virtual Earth Day summit that the world's largest economy will cut emissions blamed for climate change by 50 to 52 percent by 2030 compared with 2005 levels.

"The cost of inaction keeps mounting. The United States isn't waiting," Biden told a two-day summit of 40 leaders including the presidents of China and Russia.

"We have to step up," Biden said. "We have to take action — all of us.”

Biden's early and aggressive environmental push marks a drastic shift from his predecessor Donald Trump — but quickly raised questions on whether the United States can keep promises if another climate-skeptic president is elected in the future.

John Kerry, the former secretary of state who has become Biden's globe-trotting climate envoy, said that with the new pledges, more than half the world's economy has committed to action to keep the planet's temperature within 1.5 degrees Celsius (2.7 Fahrenheit) above pre-industrial times, the aspiration set in the Paris Agreement to avoid the most severe effects of climate change.

Japanese Prime Minister Yoshihide Suga, who discussed climate last week when he was Biden's first foreign guest, significantly raised the goals of the world's second largest developed economy to cutting emissions by 46 percent in 2030 compared with 2013.

Canadian Prime Minister Justin Trudeau, another early ally of Biden, boosted ambitions of his energy-exporting country to reductions of 40-45 percent below 2005 levels, compared with an earlier target of 30 percent.

"We must take action now. Because there's no vaccine against a polluted planet," Trudeau said.

The European Union this week confirmed its own ambitious goals and former bloc member Britain on the eve of Biden's summit released the most far-reaching targets of any major economy with 78 percent cuts from 1990 levels by 2035.

(With input from agencies)