After months of speculation, it might finally be happening: President Trump appears ready to withdraw the United States from the 2015 Paris climate agreement. If he does, he will place Washington at odds with virtually the entire international community.

I will be announcing my decision on the Paris Accord over the next few days. MAKE AMERICA GREAT AGAIN!

Despite the excited tone of Trump's tweet (and reports suggesting that he had made up his mind), the matter seemed far from settled at the time of writing. The president's daughter, Ivanka Trump, and Secretary of State Rex Tillerson are supposedly urging Trump to stick with the Paris agreement. A host of big companies have urged Trump to reconsider withdrawing. On Wednesday, the shareholders of ExxonMobil, Tillerson's former company, voted by a wide margin for a resolution they say will compel the oil giant to stick to the goal of transitioning to a low-carbon economy. Many analysts also point to how clean energy is fueling job growth: There are already twice as many solar jobs as there are coal jobs in the United States.

Their opponents include White House chief adviser Stephen K. Bannon and Environmental Protection Agency Administrator Scott Pruitt, a climate skeptic who has already set about dismantling Obama-era regulations on the U.S. fossil fuel industry. Trump seems inclined toward the Bannon and Pruitt position, which has some — though not unanimous — support from the Republican Party. (Only in the United States, of course, is the question of climate change subject to partisan debate.)

Championed by the Obama administration, the Paris agreement created, for the first time, a single framework for developed and developing countries to work together and reduce greenhouse gas emissions. The New York Times has a helpful primer on what the landmark accord entailed:

“Under the Paris agreement, every country submitted an individual plan to tackle its greenhouse gas emissions and then agreed to meet regularly to review their progress and prod each other to ratchet up their efforts as the years went by,” explained the Times. “Unlike its predecessor treaty, the Kyoto Protocol, the Paris deal was intended to be nonbinding, so that countries could tailor their climate plans to their domestic situations and alter them as circumstances changed. There are no penalties for falling short of declared targets. The hope was that, through peer pressure and diplomacy, these policies would be strengthened over time.”

If the United States withdraws from the accord, it would find itself in farcically lonely company. The pact was signed by 195 countries, with only Nicaragua and Syria bowing out.

In coastal, low-lying Nicaragua's case, leaders refused to sign because the pact didn't go far enough. “Nicaragua's lead envoy explained to reporters that the country would not support the agreed-upon plan as it hinged on voluntary pledges and would not punish those who failed to meet them,” wrote my colleague Adam Taylor.

As for Syria, the country “was effectively an international pariah when the Paris accord was first signed, making Damascus's involvement at the least impractical,” wrote Taylor. Numerous officials in President Bashar al-Assad's regime are the subject of international sanctions that limit their movement, and the ongoing, devastating war in the country means the Syrian government isn't paying much attention to limiting its emissions.

President Trump has decided to pull the U.S. out of the Paris Agreement. Here's what you need to know. (Daron Taylor/The Washington Post)

The implications of a U.S. withdrawal, though, are profound and far-reaching.

“A U.S. withdrawal would remove the world’s second-largest emitter and nearly 18 percent of the globe’s present day emissions from the agreement, presenting a severe challenge to its structure and raising questions about whether it will weaken the commitments of other nations,” wrote Washington Post environment reporter Chris Mooney.

Some climate experts actually suggest that, given Trump's steady dismantling of environmental protections, it's better for the United States to leave the pact altogether than to undermine it from within.

But given the importance of U.S. investment in clean energy, as well as the huge effect U.S. emissions have on the environment, experts warn that the international community's efforts to limit global warming to about 2 degrees Celsius may founder without U.S. compliance. The effects would be felt by vulnerable communities all around the world.

If Trump goes ahead and pulls the United States out, it would be “a decision made for domestic political purposes that puts the livelihood and lives of millions of people in developing countries at risk,” said Trevor Houser, a former climate negotiator for the Obama administration, to Vox's Jim Tankersley. “This is a craven, symbolic political move without any direct benefits for the constituents he’s targeting.”

Climate change is an existential threat to our future—staying in #ParisAgreement is the best way to protect our children & global leadership

Although the Paris agreement is nonbinding, it may take three to four years to formally withdraw. Trump could expedite the process by quitting the U.N. Framework Convention on Climate Change, signed by President George H.W. Bush and ratified by the Senate in the early 1990s, which laid the foundation for the Paris accord. "But that is a more radical move, which would further withdraw the United States from all international climate change negotiations," wrote Mooney.

And that's the other effect of a withdrawal: the disappearance of U.S. leadership on a fundamental issue affecting the future of the planet. Already, other countries are taking the mantle once donned by Obama. Ahead of a Friday meeting between European Union leaders and Chinese Premier Li Keqiang, Beijing and Brussels issued a joint statement saying they were “determined to forge ahead” with measures to “lead the energy transition.” The statement, seen by the Financial Times, also stressed a point seemingly lost on the Trump administration: “Tackling climate change and reforming our energy systems are significant drivers of job creation, investment opportunities and economic growth.”

At a time when the world focuses its efforts to reckon with global warming, Trump may really leave the United States out in the cold.