The agreement won't fall apart overnight. Already, reports suggest China and the European Union are prepared to publicly recommit to the agreement with or without the United States. Some experts say China appears to be reducing emissions ahead of schedule, in part because the country is phasing out coal quicker to reduce choking smog in its major cities.
Trump also can't technically withdraw from the agreement until November 2019. It's possible he could speed things up by abandoning the underlying Senate-approved climate treaty that the agreement is linked to.
It's an open question whether the United States will hit its Paris emissions target with or without the agreement. The economy is already moving away from carbon-heavy energy sources like coal in favor of cleaner natural gas and increasingly affordable renewable energy. Trump's actions may not be enough to alter that trend. In addition, states like California have pledged to pick up the slack if Trump withdraws by instituting their own environmental restrictions.
It's also notable that some of the largest companies in industries that would be impacted most by climate regulation are supporting the Paris Agreement. For example, ExxonMobil, the oil giant whose former CEO Rex Tillerson is now Secretary of State, has publicly lobbied the White House not to withdraw.
"I actually think we might meet our target," J. Timmons Roberts, an environmental studies professor at Brown University, told NBC News. "The technology is making the choices easier for people more quickly than expected."
But supporters of the agreement warn the United States would, at a minimum, damage its relationship with close allies by bolting and cede more global influence to rivals like China. In a worst-case scenario, the move would discourage developing nations from taking further steps to limit emissions, potentially hampering efforts to reduce emissions before dangerous temperature increases are locked in.
A lot of this depends on expectations. If participating nations and industry leaders assume the United States exit is only a temporary bump and that future presidents will return to the table and pursue similar policies as Obama, that could also make them reluctant to make decisions based on Trump's decision alone.
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