On the same day that the U.S. officially withdrew from the global pact to reduce emissions that cause climate change, presidential contender Joe Biden committed that he would rejoin the Paris Agreement if elected.

In a tweet late Wednesday, Biden wrote, “Today, the Trump Administration officially left the Paris Climate Agreement. And in exactly 77 days, a Biden Administration will rejoin it.”

The Trump Administration announced that the U.S. would leave the agreement three years ago, in a move that was blasted by venture investors at the time.

“I have always believed that, while we can disagree on the scientific premise behind climate change, we should all agree that advanced energy technologies represent one of the biggest economic opportunities,” said General Catalyst managing director Hemant Taneja at the time. “To give that up is a threat to American prosperity … Our American companies will be at a huge competitive disadvantage globally if they don’t have a market to rely on in their backyard.”

Biden’s decision to rejoin the agreement should come as no surprise given the $2 trillion climate stimulus package that was a major plank of the former Vice President’s campaign.

For the Trump Administration, the official abandonment of the climate agreement was the fulfillment of a campaign promise made in what could be the waning days of its authority.

A permanent American exit from the climate accord would be a huge blow to the international community’s ability to stave off a climate disaster caused by rising temperatures related to greenhouse gas emissions. A year of wildfires, flooding and other climate-related catastrophes have shown how changing temperatures are already wreaking havoc on communities. As the second largest emitter of global carbon dioxide, the U.S. plays an outsized role in the success of any climate change mitigation plan.

The agreement, a centerpiece of the previous Obama Administration in which Biden served as vice president, was designed to limit the emissions that cause global warming so that temperatures would not rise beyond another 2 degrees celsius.

“If Biden wins, then the fact that the withdrawal became final on November 4 really won’t matter,” Todd Stern, who was the top U.S. climate negotiator during the Obama administration, told the Financial Times. “If Trump wins a second term, then it will have much more lasting impact.”

To date, the U.S. is the only country that has formally left the agreement.

Even if a Trump Administration were to eke out a slight electoral college victory and return for a second term, market dynamics could mute the effect of any fossil fuel industry advocacy or stimulus the government may try to initiate.

Simply put, renewable energy is making more economic sense within the U.S. than its fossil fuel competitors. Wind and solar are now basically cost competitive or cheaper than fossil fuels in many markets. The cost of battery storage is also falling dramatically.

A March report from Consumer Reports explained just how much better solar power can be for consumers. “Going solar is a money-saver in the long term, even though startup costs are higher for the consumer,” according to the publication. “Electricity from fossil fuels costs between 5 cents and 17 cents per kilowatt-hour. Solar energy costs average between 3 cents and 6 cents per kilowatt-hour and are trending down, according to the National Renewable Energy Laboratory.”

Beyond market forces, a recalcitrant Trump Administration could be pressured to adopt more aggressive policies to reduce its emissions by international tariffs and potential sanctions, Sarah Ladislaw, a director of the climate change program at the Center for International and Strategic Studies at Tufts University, told the Financial Times..

“It is quite likely that other countries with ambitious emissions reduction targets, like the EU and China, will try to influence US behavior through cross-border carbon tariffs and a push to influence the global financial system to incorporate climate considerations,” she said.