Officially, Mr Trump's removal of the nation from the worldwide global climate pact stood for only 107 days.
"This includes the United States doing its fair share to keep global temperature rise to 1.5°C and providing climate finance for developing countries in line with science, equity, and justice", said Orenstein.
In Biden's first month in office, he has set up a cabinet created to consider climate concerns in all USA policy-making, and pushed through a range of executive orders to reverse Trump policies widely seen as hurting the climate and environment.
He held a news conference on Thursday, one day before the United States rejoins the pact.
Mr Biden has promised to chart a path toward net-zero U.S. emissions by 2050.
"The climate crisis is deepening and this is the year we need all major polluters to step up and deliver stronger plans to deliver a safe, clean and prosperous future for everyone", said Laurence Tubiana, France's climate change ambassador and special representative for COP21.
One fear was that other nations would follow America in abandoning the climate fight, but none did, Ms Figueres said.
"The Paris Agreement is an unprecedented framework for global action", Secretary of State Antony Blinken said in a statement Friday.
She added that the real issue was four years of climate inaction by the Trump administration, as American cities, states and businesses still worked to reduce heat-trapping carbon dioxide but without the federal government. "It's not about how many days".
"We've lost too much time". But Kerry and other members of the Biden administration have signaled they intend to go well beyond that as they seek to re-establish their climate credibility with world leaders after four years of environmental rollbacks during the Trump administration.
He also said he hopes the emissions reduction targets the USA presents to the United Nations will help guide other countries.
We can no longer delay or do the bare minimum to address climate change. "It is vital in our discussions of national security, migration, global health efforts, and in our economic diplomacy and trade talks".
The Biden administration is crafting new regulations and incentives aimed at speeding the deployment of clean energy and transitioning from fossil fuels.
Richard Black, head of the Energy and Climate Intelligence Unit (ECIU) said the USA was "back in the game like a linebacker after a time-out - sleeves rolled up, game face on, getting down to business".
That may include India setting a net-zero emissions goal, to match similar mid-century targets now declared by many countries from the United States to China, Japan and South Korea, Rachel Kyte, a leading climate and energy expert, told media this week.
Almost 200 nations have signed on to the landmark accord and committed to limit their greenhouse gas emissions in an attempt to keep global warming below 2 degrees Celsius - preferably below 1.5 degrees Celsius - compared to pre-industrial temperatures.
The U.S. rejoining the Paris accord and coming up with an ambitious target for emissions cuts would make limiting warming "to well below 2 degrees - not just to 2 degrees but below 2 degrees - a lot more likely", said climate scientist Zeke Hausfather, energy and climate director for the Breakthrough Institute.