As votes in the US presidential election continue to be counted, with no clear winner yet projected, the United States has officially exited the Paris climate agreement. Whether that decision becomes permanent or is easily reversed depends on a handful of ballots in only four states.

Donald Trump, who is in a nail-biting race for the White House against Democrat challenger Joe Biden, announced four years ago his intentions to withdraw from the agreement – the first truly global accord aimed at reducing global temperatures to avert the worst of climate change. On Wednesday, amid a bitterly contested election marked by disagreements over climate change, that withdrawal became formal.

The deal is meant to keep temperatures from rising more than 1.5C to 2C above the average before industrialization. Scientists agree that the planet is more than 1C hotter than it was before industrialization, largely because of humans burning fossil fuels.

Leading up to this year’s election, the US has been buffeted by climate-related catastrophes, from heatwaves to floods, from record setting wildfires on the West Coast to a hyperactive hurricane season in the Atlantic Ocean – issues that put the question of climate change in presidential debates for the first time in 12 years.

Trump ran on a campaign pledge set five years ago during his first run for president to end US involvement in a climate accord he considered an unfair deal for the country.

Biden, by contrast, has promised to reenter the accord on “day one” should he take the White House. He likewise said he will pressure China, Brazil and other countries to cut their own emission and preserve their forests, which keep carbon out of the atmosphere.  His domestic climate plan – the most ambitious ever put forward by a major party presidential candidate ­– allocates $2 trillion during his first term to make the US run on completely clean energy by 2035.

But commentators in the US agree that America’s formal withdrawl from Paris is a step in the opposite direction.

“The US leaving the Paris climate agreement demonstrates what’s at stake in this election,” May Boeve, executive director of 350.org, an international environmental organization, told The Washington Post. “What we need now is all hands on deck for global climate leadership.”

Should he win, however, Biden’s ambitions may well be thwarted by the US Senate, which as of Thursday midday appeared to be leaning towards remaining in Republican control.

Trump, by all indications, would likely intensify his efforts to expand the use of fossil fuels, undermine climate science, and roll back environmental protections. In the days before the November 3 election day, the Trump admiration removed the chief scientist at the National Oceanic and Atmospheric Administration, the nation’s premier scientific agency – a move seen as a sign of things to come.

By this year, the administration had sought to roll back nearly 100 US environmental protections, though the majority of those efforts are tied up in court.

Should Trump emerge as the victor when all the votes are counted, US climate action would face “a huge uphill battle” Kate Larsen, a director at the independent research firm the Rhodium Group, told The Guardian.

“It would mean that any progress we will see will come from states and cities and companies that are trying to pick up the slack,” Larsen said. “It will come nowhere close to what is needed, to what we will be able to do with a mobilized federal government.”

Still, many local politicians and business leaders have been fighting exactly that battle since Trump took office in 2016.

After Trump made clear his intention to withdraw from the agreement, the billionaire media mogul Michael Bloomberg and former California Governor Jerry Brown  launched America’s Pledge, an effort to keep the United States on track with the goals of the global accord and encourage municipalities and businesses to help make up for the lack of federal action.

To that end, California, New York and 21 other states, as well as the District of Columbia, so far have set economy-wide greenhouse gas emissions targets, according to the Center for Climate and Energy Solutions. Some of those commitments were done through executive orders from governors, while others are legislatively binding.

Even if Biden wins, it remains to be seen how much clout the United States can bring to negotiations after four years of Trump, who at times has dismissed climate change as a “hoax.”

But were the US to reengage with the Paris climate agreement, it could pressure allies like Japan, Canada and Australia to step up their efforts, Pete Betts, a former lead climate negotiator for the EU and the UK told The Guardian. Further, a Biden administration could work with the EU and China to agree on bigger targets.

Under a US president who pushes for climate policies the world could work toward “marginal, incremental damages” rather than catastrophic ones, Jonathan Pershing, program director of environment at the William and Flora Hewlett Foundation, who was the former special envoy for climate change at the US Department of State during the second term of the Obama administration, told CNN.

Pershing added: “Every succeeding election becomes more and more urgent because the time is shorter to manage those really grievous damages.”