Another important date looms on the calendar this coming week in addition to a national election billed as the most pivotal in decades. On Wednesday, the United States is set to become the only nation to officially withdraw from an international pact aimed at slowing climate change.

The exit of the world’s largest economy — and the second biggest emitter of greenhouse gases after China — comes three years to the day after President Trump began the drawn-out legal process of withdrawing the nation from the 2015 Paris climate accord.

But whether the U.S. exit turns out to be brief or lasting depends on the outcome of the presidential contest. A second Trump term would make clear that an international effort to slow the Earth’s warming will not include the U.S. government. Democratic presidential candidate Joe Biden, meanwhile, has vowed to rejoin the Paris accord as soon as he is inaugurated, and to make the United States a global leader on climate action.

Presumptive Democratic presidential nominee Joe Biden made his pitch to combat the climate crisis in a speech on July 14, targeting President Trump’s rollbacks. (The Washington Post)

For observers overseas, much as for voters in the United States, the differences could hardly be more stark, the stakes hardly higher.

“For us, it could be a matter of survival,” said Carlos Fuller, the lead negotiator for Alliance of Small Island States, a group of 44 islands and low-lying coastal states around the world that act as a bloc at international climate talks.

Sea level rise is already threatening the ability of some island nations in the Pacific, such as Tuvalu and the Marshall Islands, to remain habitable, he said. In the Caribbean, ocean acidification and swelling seas are driving coral reefs toward extinction and imperiling fishing and tourism.

“The next 10 years for us are crucial,” Fuller said. “It’s imperative that we take action now.”

Trump’s election in 2016 surprised delegates who had gathered in Morocco to begin hashing out how to implement the sweeping promises the world had agreed to a year earlier in Paris. And his swift reversal in priorities upended the previous U.S. role in nudging nations to do more to combat global warming.

In the year-long run-up to the Paris climate agreement, President Barack Obama raised climate change in virtually every meeting with a foreign leader. “No nation, large or small, wealthy or poor, is immune,” he said in one U.N. speech.

Trump, by contrast, has repeatedly questioned the science around climate change and looked upon international cooperation as both suspect and expensive. Because of the complicated rules of the Paris agreement, the U.S. exit took until the final days of Trump’s term to complete. But his mind has been made up since June 1, 2017, when he announced that the United States would bow out.

Even before officially exiting, the Trump administration has damaged the Paris framework.

While pursuing an “America First” foreign policy, it has not made payments to the Green Climate Fund, which was created to help developing countries adapt to and mitigate the impacts of climate change. It has blocked progress at the Arctic Council, the intergovernmental group that grapples with climate-fueled problems facing governments and indigenous communities in one of the world’s fastest-warming regions.

It has teamed up with oil and gas-rich Russia and Saudi Arabia to water down language about the urgency of climate change during international negotiations. It has failed to file, as the accord requires, a biennial accounting of total U.S. greenhouse gas emissions from man-made sources — and what is being done to reduce them. And the U.S. retreat, many people here and abroad worry, has given license to some other countries to slow their own promises to more rapidly cut their emissions.

Moreover, the United States has failed to provide the leadership needed to accelerate the international commitments to reduce greenhouse gas emissions enough to keep the world “well below” 2 degrees Celsius (3.6 Fahrenheit) of warming compared to the late 19th century. That’s the threshold beyond which scientists say the planet will suffer irreversible, catastrophic damage.

Even before Trump became president, the United States looked certain to miss its own Paris accord commitment to lower carbon emissions 26 percent to 28 percent below 2005 levels by 2025.

But the Trump administration has widened that gap, even with the drop in economic activity resulting from the coronavirus pandemic. Trump has weakened regulations that were designed to reduce pollution generated by the United States, which accounts for about 15 percent of global carbon dioxide emissions each year. And the administration has been trying to stop states like California from taking their own steps to transition away from fossil fuels.

In Northern California, the Kincade Fire caused unprecedented evacuations and power outages. This elected official calls it ground zero for climate change. (The Washington Post)

“It is clear President Trump has slowed down global progress and ambition on climate since taking office in 2017, and if climate deniers keep the White House and Congress, delivering a climate-safe planet will be slower and more challenging,” Laurence Tubiana, a French diplomat who presided over the 2015 Paris talks and is considered a key architect of the agreement, wrote in an email.

At the same time, Trump’s abrupt reversal of U.S. climate policies and his disdain for the Paris accord have done little to outright derail the international effort. The European Union has adopted a Green Deal. Japan and Britain have announced more aggressive new targets. And China has set a goal of carbon neutrality by 2060, while Japan recently said it intends to reach that target in 2050. None of the other nearly 200 countries have followed the United States in withdrawing from the Paris agreement.

“Nobody has in the last four years, and I don’t think they will in the future,” Peter Betts, an associate fellow at the U.K. think tank Chatham House, who served as a top European Union climate negotiator, said on a call with reporters this week.

“The good news is the rest of world stayed in the Paris agreement,” Pete Ogden, vice president of energy, climate and the environment at the United Nations Foundation, said in an interview. “It shows the buy-in the agreement has even in face of the Trump administration rejecting it.”

If Trump wins reelection and keeps the United States out of the international effort to slow climate change, many experts believe that much of the country will move forward without him. Individual states already are pursuing greener energy policies, electric cars are becoming more affordable and sales are increasing, and renewable technologies like wind and solar are getting cheaper and growing rapidly.

The group America’s Pledge, founded by former California governor Jerry Brown and former New York mayor Mike Bloomberg, has calculated that a coalition of states, cities and businesses representing 70 percent of the U.S. gross domestic product will cut greenhouse gas emissions by 19 percent from 2005 levels by 2025. By implementing “bottom-up” standards, the cuts could reach as deep as 37 percent by 2030.

“Despite the Trump Administration, we’ve managed to keep our Paris targets within reach,” Bloomberg said in a statement. “But we cannot afford another four years of climate denialism and giveaways to the fossil fuel industry.”

We Are Still In, a campaign organized by the World Wildlife Foundation, says more than 3,000 corporate executives, mayors, governors, tribal leaders and others pledged to do their share to meet the U.S. commitment to the Paris accord.

“The markets and the economy are moving in one direction,” said Rachel Kyte, a British academic and dean of the Fletcher School of Law and Diplomacy at Tufts University. “I think we are at tipping points now in where capital is going. It’s just going to go faster.”

Betts agrees, saying the shifts in the “real economy” are beyond the ability of any president to halt entirely. Even Trump’s effort to save the coal business has failed to reverse that industry’s downward trend. “This transformation, this change, is irreversible,” Betts said. “It’s inevitable.”

Meanwhile, if elected, Biden has vowed to rejoin the Paris climate agreement almost immediately. He has called climate change an existential threat and proposed a four-year, $2 trillion domestic spending plan to combat climate change and environmental racism — the most ambitious blueprint ever released by a major party nominee for president.

“If Biden wins, it’s a speed bump,” Alden Meyer, a longtime expert on international climate policy, said of the Trump era.

World leaders were initially supposed to assemble the week after the U.S. election for climate negotiations in Glasgow, Scotland, but the meeting was canceled because of the coronavirus pandemic. The site where the massive conference was scheduled to take place instead was temporarily converted into a field hospital. The gathering has now been rescheduled for next year, effectively giving nations more time to update the pledges they made five years ago and promised to increase over time.

If Trump remains in the White House, the collective push to rapidly reduce global emissions as quickly as scientists say must happen in coming years could “be very challenging,” Meyer said. “It may be impossible with the United States on the sidelines.”

But if elected, Biden will need to do more than merely set a new national target and sign back onto the Paris agreement. The international negotiations are often touchy, time consuming and incremental. And the international landscape looks different than when Biden served as vice president.

The most difficult relationship he would probably face is the one with China, the world’s top greenhouse gas emitter, said Jason Bordoff, director of Columbia University’s global Energy Center. The two have been engaged in a trade dispute and a Biden administration might add human rights, cybersecurity, Taiwan and open naval waters to the points of friction.

“The key relationships have shifted. The world’s view of the United States has dimmed a bit,” Kyte said. “We’re not going back to the era that existed four years ago.”