(CNN)Bye-bye, dirty fossil fuels.
The clean-energy era is here.
That's the promise of the Paris Agreement on climate change, which 132 countries, including the United States, have ratified or accepted, pledging to make the air less deadly and to prevent the most catastrophic consequences of global warming.
Donald Trump threatens to undermine all that.
It's unclear if or when the US President might try to "cancel" the accord, as he pledged to do on the campaign trail. The United States could not actually nullify the global agreement on its own, and withdrawing from the agreement would take one to four years, depending on the approach. But that may not matter much. The White House says it wants to revive coal, oil and natural gas production, all of which pollute the atmosphere, contributing to the likelihood of mass extinction, worsening droughts, deadlier heat waves, flooded coastal cities and other climate disasters.
Because the Paris Agreement does not levy sanctions or fines against countries that fail to meet their pollution-reduction pledges, it's possible the Trump administration could choose to remain in the agreement while basically polluting as usual.
Either tactic -- defection or de facto not caring -- could weaken the pact, potentially leading other nations to defect. The United States, after all, is the second biggest annual climate polluter, after China, and helped negotiate the Paris deal.
Yet, for all those caveats, this is also true: The Paris Agreement is bigger than Donald Trump.
Some policy experts say it can and should survive, with or without the United States.
One reason for optimism: The rest of the world gets it.
US officials "stand completely alone on being climate deniers," Jennifer Morgan, executive director of Greenpeace International, told me. "If you look at the speeches from Paris, all the heads of state who came -- all -- and even fossil fuel providers, identified this as a real, science-based issue that they're working to solve together."
For evidence of this rhetorical shift, look no farther than Vladimir Putin's 2015 comments, as relayed by The New York Times: "Climate change has become one of the gravest challenges humanity is facing," Putin said in Paris. "Caused by global warming, hurricanes, droughts, floods and other anomalies are the source of economic damage."
China, too, has expressed steadfast support for climate action.
"The Paris Agreement is a hard-won achievement which is in keeping with the underlying trend of global development," President Xi Jinping said in January at the World Economic Forum. "All signatories should stick to it instead of walking away from it as this is a responsibility we must assume for future generations."
Trump, meanwhile, has denied the scientific consensus that humans are causing warming, primarily by burning fossil fuels and otherwise pumping heat-trapping gases into the atmosphere.
'Very different place'
The United States' relative isolation is one factor that could keep the Paris Agreement from becoming the Kyoto Protocol, Morgan said, referencing the 1997 climate agreement that was abandoned by the George W. Bush administration.
"We're in a very different place than we were under the Bush years when they pulled out of Kyoto, which I remember well," she told me. "The depth of the commitment to shift and transform economies was much thinner. ... The risks of climate change [today] are much more deeply understood and felt, unfortunately.
"It's not a problem of tomorrow. It's a problem of today."
The Trump administration could choose to withdraw from the Paris Agreement, but it wouldn't be able to start that process until November 2019, three years after the agreement "came into force," to use UN-speak. The Paris Agreement stipulates there is a one-year delay from that point, which would put withdrawal in late 2020.
Another option -- and a more drastic one -- would be for the United States to withdraw from the UN Framework Convention on Climate Change, a 1992 treaty that is the foundation for the 2015 Paris Agreement. Getting out of that would take one year, and it likely would be regarded as an even bolder slap in the face of countries that are trying to do something about climate change.
"Certainly it would be a far, far wiser thing to do for the [Trump] administration to stay in the [Paris Agreement] regime -- both because climate change is a very important phenomenon and a very important issue; but even independent of climate change, for the US to de facto walk away would produce all kinds of significant collateral damage," said Todd Stern, the Obama administration's special envoy for climate change, who now is a visiting lecturer at Yale Law School.
"There are tons and tons of countries all over the world, big and small, who care a whole lot about climate change, who are invested in the Paris Agreement," he continued, "and who would be very upset if we were to walk away."
'No time to waste'
Looking at "nature's math" offers a grimmer picture.
There's only so much carbon the world can pump into the atmosphere before we're assured of screwing up the targets set in the Paris Agreement, which aims to limit warming to 1.5 or 2 degrees Celsius above pre-industrial levels.
By some calculations, we're only five, 10 or perhaps 20-some years away from those red lines if the world keeps polluting at the same staggering rate.
So any new pollution is a very big deal.
While it's unclear if the United States alone could upset the Paris goals in a single presidential term, "there is no chance of limiting warming to no more than 2 degrees Celsius unless US emissions fall much more than our Paris pledge calls for, along with similar cuts for all other nations," said John Sterman, a professor at the MIT Sloan School of Management. "[A] cascade of defections from Paris," he added, "would be a fatal blow to the prospects to liming warming to no more than 2 degrees, and there would be climate catastrophes that come with that."
Working with Climate Interactive, where he is a senior adviser, Sterman calculated that the United States pulling out of the Paris Agreement, and canceling many Obama-era climate regulations, including the Clean Power Plan, would increase global temperatures on the order of a few tenths of a degree by 2100. That assumes, however, the rest of the world keeps making aggressive cuts. "Assuming that all nations, including the US, aggressively cut emissions, would yield 1.9 degrees Celsius [of warming] by 2100," he said. "But if the US does nothing, then expected warming rises to 2.2 degrees Celsius by 2100."
Those figures count on action that's bolder than what's been pledged to date. Current pledges made as part of the Paris Agreement, including US commitments, put the world at about 3.4 degrees Celsius of warming by 2100, according to Sterman and Climate Interactive. If the entire agreement fell apart and global emissions continued at their current clip, the planet could expect 4.2 degrees of warming.
That could be truly catastrophic. At 6 degrees of warming, for instance, "most of the planetary surface would be functionally uninhabitable," according to Mark Lynas, author of "Six Degrees."
There are some unknowns in these calculations, Sterman stressed, including what states like California and cities like New York will do on their own to fight climate change, absent any federal action. "But the implications are clear," Sterman wrote in an email. "To have any chance of limiting warming to no more than 2 Celsius, all nations, including the US, must aggressively cut emissions."
He added, "There's no time to waste."
'Fight another day'
The American public appears to agree.
Nearly seven in 10 registered voters in the United States say the country "should participate in the international agreement to curb global warming," according to a November 2016 survey from the Yale Program on Climate Change Communication and the George Mason University Center for Climate Change Communication.
Some of them soon will take to the streets in support of climate research and action.
On Earth Day, April 22, scientists are expected to assemble in Washington to protest, among other things, "the mischaracterization of science as a partisan issue." One week later, on April 29, climate activists plan to hit the streets again.
They're marching for "jobs, justice and the climate."
If the Trump administration scrapped the Paris Agreement, said Morgan, from Greenpeace International, it would show "disrespect for other countries that have identified this as a priority, and a lack of understanding for how important that agreement is for the safety and security of people in the Untied States."
"Does it mean the end of climate action?" she asked.
"Absolutely not. You live to fight another day."