The U.S. will withdraw from the Paris Agreement, a landmark international climate change deal reached in 2015, President Trump announced today.

This is a terrible idea. To flee now is bad for the country, bad for business, bad for humanity, bad for ecology and even bad for Trump. Here are a few reasons why.

1. The Paris Agreement is a badly needed breakthrough.

Climate change is already upending lives, ecosystems and economies around the world. Earth's air hasn't held this much carbon dioxide since the Pliocene Epoch, long before our species existed. Habitats are shifting, food security is fading, ancient ice is melting and seas are rising. Climate change can occur naturally, but thanks to our excess CO2, it's happening at a scale and scope unseen in human history.

Yet as bad as it is now, the worst is reserved for our descendants. CO2 emissions can stay in the sky for centuries, and of course we're releasing more all the time. Plus, as reflective polar ice melts, Earth can absorb more and more heat from sunlight.

After decades of slow negotiations, 195 countries finally agreed on a plan in late 2015 to collectively reduce CO2 emissions. The resulting Paris Agreement is far from perfect, but it's a leap forward in our ability to unite against global disaster.

Given the stakes involved, and the work required to get this far, the Paris Agreement is a "monumental triumph for people and planet," as former U.N. Secretary-General Ban Ki-moon said in 2015. It has detractors, of course, but the objections cited by some critics in the U.S. suggest serious confusion about how the deal works.

2. The Paris Agreement is broadly popular, both at home and abroad.

Only two countries didn't sign the Paris Agreement: Syria and Nicaragua. Syria abstained due to its long-running civil war (although other war-torn countries like Iraq and Yemen managed to sign, as did isolated North Korea). Nicaragua, on the other hand, protested the agreement for not going far enough. It wanted legally binding emissions limits, arguing that "voluntary responsibility is a path to failure."

Syria and Nicaragua have small carbon footprints, and weren't sorely missed from a coalition that featured 195 other countries, including top emitters like China, Russia and India. But the U.S. helped bring that coalition together, and it's also the world's No. 2 CO2 emitter, so its reversal may inspire more animus around the world.

But abandoning the agreement isn't just a retreat from the global community. It also defies popular opinion at home. Seventy percent of registered U.S. voters say the U.S. should participate in the Paris Agreement, according to a nationally representative survey conducted after the 2016 election by researchers from Yale University. That stance is shared by a majority of voters in every U.S. state, the poll found, and is even shared by about half of those who voted for Trump.

3. It's broadly popular with American businesses, too.

The Paris Agreement has huge support from corporate America, and not just passive support: Powerhouse U.S. companies have actively pushed the U.S. to stay in the deal. Dozens of Fortune 500 companies have spoken out in favor of staying, and 25 of them — including tech titans Apple, Facebook, Google and Microsoft — recently ran full-page ads in major U.S. newspapers urging Trump to do the right thing.

Another group of 1,000 big and small U.S. companies also signed a letter with a similar message, expressing their "deep commitment to addressing climate change through the implementation of the historic Paris Climate Agreement." Prominent names in that last include Aveda, DuPont, eBay, Gap, General Mills, Intel, Johnson & Johnson, Monsanto, Nike, Starbucks and Unilever, to name a few.

Even top U.S. oil companies called for Trump to stay in the accord. ExxonMobil, the country's largest oil company, officially supports it, and CEO Darren Woods sent Trump a personal letter expressing that view. ExxonMobil is joined in this position by fellow oil giants BP, Chevron, ConocoPhillips and Shell, and even by a major coal firm, Cloud Peak Energy, whose CEO also wrote a letter asking Trump not to withdraw.

Overall, the U.S. businesses that support the deal represent more than $3.7 trillion in total annual revenue, according to Ceres, and employ more than 8.5 million people.

4. It isn't legally binding. A country can set any emissions target it wants.

Many critics argue the Paris Agreement will limit economic growth and "kill jobs." That would be a pretty outdated fear even under strict emissions limits, given the decline of coal and the growth of cleaner power sources like natural gas, solar and wind. There are already twice as many solar jobs in the U.S. as coal jobs, and job growth in solar and wind power is now 12 times faster than the U.S. economy overall.

But despite a common misconception, there are no legally binding limits in the deal. Countries do have to submit emissions targets, called nationally determined contributions (NDCs), but they're merely encouraged to set ambitious targets. It would be easy to go unconstrained by the deal without melodramatically bailing out.

"By remaining in the Paris Agreement, albeit with a much different pledge on emissions, you can help shape a more rational international approach to climate policy," Cloud Peak Energy CEO Colin Marshall wrote to Trump in April. "Without U.S. leadership, the failed international policies that have characterized the past 25 years will continue to predominate. Addressing climate concerns need not be a choice between prosperity or environment."

5. The key to the Paris Agreement is transparency.

Countries are free to set any emissions targets they want, but they do have to set transparent targets for the world to see. And the gist of the Paris Agreement is that peer pressure should make countries want to set reasonable targets. It's not ideal, but after decades of negotiations, it's a major achievement.

So if the U.S. had stayed in the agreement but set an easy emissions target, it might have faced international pressure to do more. But it would've still had a "seat at the table," as many supporters have argued, and that pressure would likely pale in comparison to the loss of international influence from leaving the deal altogether.

On the other hand, a few experts say a U.S. exit might actually be better for the agreement, given Trump's stance on climate action. Staying but setting easy targets, they argue, could provide cover for other countries to do the same, thus eroding the effect of peer pressure. They may have a point, although even if the absence of a Trump-led U.S. is better for the deal, it's almost certainly worse for America.

6. Walking away has no strategic value.

As the No. 2 emitter of CO2, the U.S. is inevitably making waves by leaving the Paris Agreement (which, notably, will take four years). But, thanks partly to Obama-era diplomacy, No. 1 emitter China is part of the deal after decades of resistance. So are all other countries but two. It's possible the U.S. exit will spur other countries to leave, but many observers expect the agreement to forge ahead regardless.

Quitting the Paris Agreement, therefore, is essentially giving up. After developing a leadership role in global climate talks, the U.S. is ceding that leadership to China and other countries — and without getting anything in return.

"President Trump appears to be heading toward a deeply misguided decision that would be bad for the world, but even worse for the United States," says Andrew Steer, president and CEO of the World Resources Institute, in a statement. "Sadly, President Trump appears to be falling for 20th-century economic thinking, when more efficient, cleaner 21st-century opportunities are there for the taking."

"In withdrawing," Steer adds, "he would relinquish U.S. leadership."

Trump fulfills a campaign pledge by leaving the Paris Agreement, but he also undermines his "America First" pledge by weakening the country's credibility and influence. And that's hardly the only way this move could backfire on its supporters. They, like everyone else, must eventually hand over the Earth to their children and grandchildren. And even if they don't feel the effects of climate change in their own lifetimes, it's unlikely this dawdling won't one day catch up to their progeny.

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While leaving the Paris Agreement is widely seen as a blunder, there are still reasons to be optimistic about the agreement itself, with or without U.S. participation. Other countries remain on a clearer path to reining in their CO2 emissions, and the leadership void left by the U.S. can be filled by China, Europe and others. Plus, this kind of political posturing is unlikely to fully derail recent progress in the U.S., either. According to Todd Stern, the former chief U.S. climate negotiator who played a key role in creating the Paris deal, there's already too much momentum.

"In the United States, the already strong efforts of our states and cities will loom even larger, demonstrating to ourselves and the world our commitment to confront climate change," Stern writes in the Atlantic. And along with action from cities, states, businesses and investors, he adds, the American public also "needs to ramp up even more, to stay engaged or get engaged, and make clear to politicians at every level that rejecting strong climate action will cost them on election day."

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.