"Let us mobilize political leadership to move ahead together - to overcome climate change, end our war on nature and build lives of dignity and prosperity for all", the United Nations chief told world leaders attending the Leaders Summit on Climate.
Biden's early environmental push marks a drastic shift from his predecessor Donald Trump - but quickly raised questions on whether the United States can carry out its promises if another climate-skeptic president is elected in the future.
"President Biden has come through with a bold emissions reduction target that should make the world sit up and take note", Manish Bapna, interim president and CEO of the World Resources Institute, said in a statement.
British Prime Minister Boris Johnson called the new US goal "game changing" as two other countries made new pledges.
Some climate activists have said Biden needs to do even more, however, pointing out that the U.S. is lagging after four years of Trump and the rest of the world has made scant progress to date in cutting emissions, with greenhouse gases already rising again after a dip last year due to pandemic-related shutdowns.
The meeting was, however, an impressive gathering of the world's most powerful leaders speaking on the single cause of climate change.
Leaders need to translate those commitments into concrete and immediate action, he said, adding that, so far, only 18-24% of pandemic economic recovery spending is expected to contribute to mitigating emissions, reducing air pollution or strengthening natural capital. "And that's where the whole world is still way off course".
However the world's three biggest carbon emitters - the US, China and India - have yet to update their national contributions to achieve this.
British PM Boris Johnson not to visit India in view of pandemic
Johnson said it was "only sensible" to postpone the trip, "given what's happened in India , the shape of the pandemic there". The Health Ministry also reported 1,619 deaths from COVID-19 in the past 24 hours, pushing the toll over 178,769.
President Xi Jinping promised a year ago that China would go carbon neutral by 2060 but environmentalists note that it has gone slow on reducing coal - which is the dirtiest form of energy but carries political sensitivities due to mining jobs.
But environmentalists have voiced alarm at China's slow pace of retiring coal, which is the dirtiest form of energy but politically sensitive due to mining jobs. And, he said the costs of not stopping the problem were growing.
The president, seeking to urge emerging economies into action on addressing the climate emergency, also said that by 2024 Washington will double its annual public financing commitments to developing countries.
The US is the largest historic emitter of greenhouse gas emissions. Sector-specific goals will be laid out later this year.
The new US pledge is aimed at encouraging industrializing countries including China, India and Brazil that account for much of the world's carbon output to set their own aggressive emissions-reductions targets.
How Washington intends to reach its climate goals will be crucial to cementing USA credibility on global warming, amid worldwide concerns that America's commitment to a clean energy economy can shift drastically from one administration to the next.
British Prime Minister Boris Johnson called Biden's pledge "a game-changer" that will "have a transformative impact in the global fight against climate change". That serves as the deadline for almost 200 countries to update their climate pledges under the Paris agreement, an global accord set in 2015.
Leaders of smaller states and island nations buffeted by rising seas and worsening hurricanes appealed for aid and fast emissions cuts from world powers.
Scientists say major polluters must be carbon neutral by the middle of the century in order to meet the Paris Agreement goal of limiting warming to "well below" 2 degrees Celsius.