* U.S. pledges to slash emissions 50%-52% by 2030
* Britain's Johnson calls new U.S. goal "game changing"
* Japan pledges 46% cut, Canada 40%-45% reduction
* White House has yet to set specific targets by industry (Adds details on Japan and Canada's new goals)
By Jeff Mason and Valerie Volcovici
WASHINGTON, April 22 (Reuters) - The Biden administration on Thursday pledged at a U.S. climate summit attended by world leaders to slash U.S. greenhouse gas emissions in half by 2030, a target it hopes will spur other big countries to raise their ambition to combat global warming.
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. President Joe Biden unveiled the goal to cut emissions by 50%-52% from 2005 levels at the start of a two-day virtual climate summit attended virtually by leaders of 40 countries including China, Russia and India.
"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 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 raised his country's goal to a cut of 40%-45% by 2030 below 2005 levels, up from 30%.
The U.S. climate goal also marks an important 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 they fear will damage the economy.
The U.S. emissions cuts are expected to come from power plants, automobiles, and other sectors across the economy, but the White House did not set individual targets for those industries. The target nearly doubles former President Barack Obama's pledge of an emissions cut of 26-28% below 2005 levels by 2025. Sector-specific goals will be laid out later this year.
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.
"With a transparent price on carbon and innovation, we can make measurable climate progress within this decade without hurting America's middle-class, jeopardizing U.S. national security, and undermining economic recovery," said Mike Sommers, API's president and CEO.
Biden focused on restoring U.S. climate leadership during his campaign and in the first days of his presidency after Republican Trump, a climate change skeptic, removed the United States from the Paris agreement on global warming.
'THE U.S. IS BACK'
The new administration has come under heavy pressure from environmental groups, some corporate leaders, the UN secretary general and foreign governments to set a target to cut emissions by at least 50% this decade to encourage other countries to set their own ambitious emissions goals.
The summit was attended by leaders from the world's biggest emitters, including China.
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.
"When we close this summit on Friday, we will unmistakably communicate ... the U.S. is back," he said.
(Reporting by Jeff Mason and Valerie Volcivici; writing by Timothy Gardner; Editing by Lisa Shumaker and Raissa Kasolowsky)
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