The United States and other countries hiked their targets for slashing greenhouse gas emissions at a global climate summit hosted by President Joe Biden, an event meant to resurrect U.S. leadership in the fight against global warming. 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.