President Donald Trump has officially withdrawn the U.S. from the Paris Agreement on climate change, a move Democratic presidential candidate Joe Biden has said he would reverse if he wins the election.

Despite Trump's official withdrawal from the international climate deal, the nation's future potential involvement in it remains in question given that Biden has pledged to rejoin the accord on his first day in office if he wins the election.

Voting in the U.S. presidential election concluded on Nov. 3, but the outcome is still unclear in several key battleground states given that many people cast their vote by mail-in ballot due to COVID-19 health concerns. Swing states yet to report results include Pennsylvania, Michigan, Wisconsin, Georgia and Nevada.

The U.S on Nov. 4 officially exited the accord after Trump had formally launched the process one year prior. Nov. 4, 2020, was the first day the U.S. could officially withdraw, but Trump had signaled plans to make the move in 2017. Trump has said the Paris accord is harmful to U.S. workers and the economy.

Trump has also questioned the connection between human-caused greenhouse gas emissions and climate change and his administration rolled back several key Obama-era environmental regulations, actions that are projected to add about 1.8 billion tons of carbon dioxide equivalent emissions to the atmosphere by 2035.

At the same time, at least two reports by U.S. federal agencies during Trump's term have warned that climate change, if left unchecked, could substantially damage the U.S. economy. Those forecasts were included in the government's Fourth National Climate Assessment in November 2018 and, more recently in October 2020, by a panel that the Commodity Futures Trading Commission convened.

A number of investor groups, company executives and the heads of some nations have suggested that the U.S.' leadership role on climate change on a global scale could encourage other companies to follow suit. The Business Roundtable, a group comprised of CEOs of the nation's largest publicly traded companies, in September called for international cooperation and diplomacy backed by a broadly supported U.S. policy. The group also said it supports a federal price on carbon dioxide emissions.

As for some other nations, Carlos Fuller, the lead climate change negotiator for the Alliance of Small Island States — a coalition of 44 developing countries — recently said that if Trump is elected to another term and has pulled from the Paris accord, limiting global warming to 1.5 degrees C relative to pre-industrial levels would be much harder.

"It would mean other countries would have to redouble their efforts," Fuller said.

Yet even as the U.S. government has declined to take a lead role on international climate negotiations, the leaders of China and Japan in recent weeks have amped up their efforts to combat climate change and European policymakers continued to pursue climate policies.

Steps to rejoining the Paris accord

While Biden can sign the accord on his first day in office if he wins the election, the language of the agreement reached among more than 190 countries in 2015 indicates that a new participant is not officially a part of the accord until 30 days after signing it.

In addition, the U.S. will need to retake a number of steps it made the first time it was part of the agreement, including designating its emissions reduction targets known under the agreement as a nationally determined contribution, or NDC, according to academic legal experts. Trump leaving the accord effectively also cancels whatever NDC the U.S. previously submitted, Susan Biniaz, a former climate negotiator for the U.S. who now teaches at Yale Law School, wrote in a March 2020 blog posted by the Columbia Law School Sabine Center for Climate Change Law.

But "in contrast to signing up for the agreement itself, the development of an NDC is likely to involve the consideration and balancing of various objectives," Biniaz wrote.

One big decision to make would be how fast the U.S. should submit its NDC, Biniaz said. Biden has pledged to set the U.S. on a path to achieve economywide net-zero emissions but if he submits a highly ambitious NDC without having pursued domestic law and engaged with domestic stakeholders and other countries first, the NDC "might lack in credibility." But a more credible target developed over time "might lack in ambition," she wrote.