Biden unveiled the goal to cut emissions by 50%-52% from 2005 levels at the start of a two-day climate summit kicked off on Earth Day and attended virtually by leaders of 40 countries including big emitters China, India and Russia.

The United States, the world's second-leading emitter after China, seeks to reclaim global leadership in the fight against global warming after former President Donald Trump withdrew the country from international efforts to cut emissions.

"This is the decade we must make decisions that will avoid the worst consequences of the climate crisis," Biden, a Democrat, said at the White House.

British Prime Minister Boris Johnson called the new U.S. goal "game changing" as two other countries made new pledges.

Prime Minister Yoshihide Suga, who visited Biden at the White House this month, raised Japan’s target for cutting emissions to 46% by 2030, up from 26%. Environmentalists wanted a pledge of at least 50% while Japan’s powerful business lobby has pushed for national policies that favor coal.

Canada's Prime Minster Justin Trudeau, meanwhile, raised his country's goal to a cut of 40%-45% by 2030 below 2005 levels, up from 30%.

Brazil’s President Jair Bolsonaro announced his most ambitious environmental goal yet, saying the country would reach emissions neutrality by 2050, 10 years earlier than the previous goal.

Greenpeace UK’s head of climate, Kate Blagojevic, said the summit had more targets than an archery competition.

"Targets, on their own, won’t lead to emissions cuts," she said. "That takes real policy and money. And that’s where the whole world is still way off course."

PUTIN SAYS PROBLEMS GO WAY BACK

Most of the countries did not offer new emissions goals. Chinese President Xi Jinping said China expects its carbon emissions to peak before 2030 and the country will achieve net zero emissions by 2060.

Xi said China will gradually reduce its coal use from 2025 to 2030. China, a leader in producing technology for renewable energy like solar panels, burns large amounts of coal for electricity generation.

Russian President Vladimir Putin proposed giving preferential treatment for foreign investment in clean energy projects, but also made an apparent reference to the United States being historically the world's top greenhouse gas polluter. "It is no secret that the conditions that facilitated global warming and associated problems go way back," Putin said.

The U.S. climate goal marks a milestone in Biden's broader plan to decarbonize the U.S. economy entirely by 2050 - an agenda he says can create millions of good-paying jobs but which many Republicans say will damage the economy.

The U.S. emissions cuts are expected to come from power plants, automobiles, and other sectors across the economy. Sector-specific goals will be laid out later this year.

The new U.S. target nearly doubles former President Barack Obama's pledge of an emissions cut of 26%-28% below 2005 levels by 2025.

CEMENTING CREDIBILITY

How Washington intends to reach its climate goals will be crucial to cementing U.S. credibility on global warming, amid international concerns that America's commitment to a clean energy economy can shift drastically from one administration to the next.

Biden's recently introduced $2.3 trillion infrastructure plan contains numerous measures that could deliver some of the emissions cuts needed this decade, including a clean energy standard to achieve net zero emissions in the power sector by 2035 and moves to electrify the vehicle fleet.

But the measures need to be passed by Congress before becoming reality.

The American Petroleum Institute, the top U.S. oil and gas lobbying group, cautiously welcomed Biden's pledge but said it must come with policies including a price on carbon, which is a tough sell among some lawmakers.

'THE U.S. IS BACK'

The summit is the first in a string of meetings of world leaders - including the G7 and G20 - ahead of annual UN climate talks in November in Scotland. That serves as the deadline for nearly 200 countries to update their climate pledges under the Paris agreement, an international accord set in 2015.

Leaders of small island nations vulnerable to rising seas, like Antigua and Barbuda and the Marshall Islands, also spoke at the summit.

World leaders aim to limit global warming to 1.5 degrees Celsius above pre-industrial levels, a threshold scientists say can prevent the worst impacts of climate change.

A Biden administration official said with the new U.S. target, enhanced commitments from Japan and Canada, and prior targets from the European Union and Britain, countries accounting for more than half the world's economy were now committed to reductions to achieve the 1.5 degrees Celsius goal.

European leaders including German Chancellor Angela Merkel and European Commission President Ursula von der Leyen expressed delight that the United States was back in the climate fight.

“The importance of this day in my judgment is the world came together,” Biden’s climate envoy John Kerry told reporters at the White House.