As of Friday, the United States has official rejoined the Paris Climate Agreement, lending new vigor to the global struggle against climate change, but politically trickier steps lie ahead as the Biden administration seeks in coming months to set tough emissions targets for the nation.

Scientists and foreign diplomats have welcomed the US return to the treaty, which became official 30 days after President Joe Biden ordered the move on his first day in office – though the administration has much ground to make up in the international community after four years of backsliding under Trump.

At present, White House officials are under pressure to identify a 2030 carbon goal within the next two months, at which point President Biden will host an international climate summit in the United States.

Altogether the U.S. spent 107 days outside the Paris Agreement, after former President Trump completed the three-year withdrawal process one day after the November election.

On Friday, speaking to a security conference in Munich, he stressed that “we can no longer delay or do the bare minimum to address climate change. This is a global existential crisis, and all of us will suffer if we fail.”

While Friday’s return to the Paris Accord is heavily symbolic, world leaders say they expect America to prove its seriousness to the cause. They are particularly eager for the United States to announce its new national 2030 target for cutting fossil fuel emissions, which scientists agree are altering the Earth’s climate and worsening the extremes of drought, hurricanes, flooding and other natural disasters.

Biden has set a deadline of April 22 to complete the pledge for 2030 emissions cuts ahead of his Earth Day summit – a gathering the administration hopes will prod other nations toward their own ambitious emissions cuts. That spring meeting should see countries start “to put the down payments on the table,” John Kerry, Biden’s climate envoy, said Friday, according to the Associated Press.

The event is meant to reintroduce the US as a world leader on climate change and raise global ambition ahead of climate talks in Glasgow, Scotland, in November.

Assuring global partners that the US will prioritize climate change – including mitigation and finance for poor countries – is key not only to the success of the Glasgow talks, but of Biden’s leader-level summit this spring, Rachel Cleetus, international climate director for the Union of Concerned Scientists, told E&E News.

Experts on US climate diplomacy have told US media that the administration has been laying the groundwork for its new emissions pledge since the fall. The pledge is expected to draw on research from nonfederal analysts and think tanks that continued work on the issue during the Trump years, when US climate progress carried on in cities, states and boardrooms while it languished in Washington.

Two of the most visible groups that formed in those years—We Are Still In, a coalition of states, cities and businesses, and America’s Pledge on Climate Change, which tracked their progress—merged today under a new name: America Is All In.

Biden also has also signed more than a dozen executive orders related to climate change, and has mobilized every federal agency to help shape the government’s response.

But with only a bare Democratic party majority in the Senate, and the opposition of most US oil, coal and gas companies, new climate legislation is expected to be a heavy lift.

University of Maryland environment professor Nate Hultman, who worked on the Obama administration’s official Paris goal, told AP he expects a 2030 target of cutting carbon dioxide emissions between 40% and 50% from the 2005 baseline levels.

A longtime international goal, included in the Paris accord with an even more stringent target, is to keep warming below 2 degrees Celsius since pre-industrial times. The world has already warmed 1.2 degrees Celsius since that time.