White bears costumed activists demonstrate near the Eiffel Tower, in Paris, Saturday, Dec.12, 2015 during the COP21, the United Nations Climate Change Conference. (AP Photo/Matt Dunham)

Update: Cruz has now indicated that he would ignore the climate agreement reached in Paris earlier this month. When it was released last week, we wrote this article explaining how that was legally possible.

On Saturday, as cities across the eastern United States set new high temperature records, negotiators in Paris approved a sweeping new agreement aimed at limiting the greenhouse gas emissions linked to climate change. Backed by a series of pledges from individual nations to cut carbon dioxide emissions and shepherded in no small part by the United States, the goal of the United Nations World Climate Change Conference was to shift the world's course onto a less-warm future.

For the Obama administration, the agreement was perhaps the largest step forward in the president's efforts to take significant action on global warming. Paired with the administration's changes to fuel efficiency, proposals to limit carbon dioxide emissions from electricity generation (his "Clean Power Plan"), the symbolic step of rejecting the Keystone XL pipeline and -- critically to the Paris discussion -- the agreement with China to cut emissions, President Obama has moved to demonstrate his and the country's commitment on the issue. And, not incidentally, bolster his legacy.

But there's an important footnote to the Paris agreement. The next president, should he or she be so inclined, can simply ignore it.

Delegates from 196 nations approved a historic climate deal after 13 days of negotiating on Saturday, Dec. 12. Here's what you need to know about the accord. (Monica Akhtar/The Washington Post)

Michael Burger, executive director of the Sabin Center for Climate Change Law at Columbia University and a lecturer at the school, spoke with me by phone on Monday and explained the legal limitations of the United States's support for the deal. "In the event of a Republican administration that wants to undo the Clean Power Plan and other domestic regulations and to void the Paris agreement," he said, "the option would be available to simply withdraw from the agreement."

The agreement, as is typical for international agreements, allows for a number of different means by which governments can accept its terms. A critical moment in the debate over its final contents arose when the word "shall" was substituted for "should" -- the former being a dictate for action and the latter being a recommendation. The United States' negotiators, led by Secretary of State John Kerry, couldn't accept a "shall" mandate -- because the negotiators understood that this would make it more likely that the agreement would require ratification from the Senate.

"It doesn't impose any new legally binding requirements on the United States or any of the signatories," Burger said. "The U.S. was very keen to avoid making the Paris agreement something that would impose any mandatory greenhouse gas emissions on the United States precisely because if it did do that it would require Senate ratification." And if the Senate got to weigh in on the agreement, it would almost certainly reject it. After all, the Senate is controlled by Republicans -- and includes among its numbers some stalwart opponents to taking action on climate change, including Sen. Ted Cruz.

In other words, the administration did what it could to ensure that the opposition couldn't kill the deal. But if Cruz is successful in his bid to succeed Obama, there's also no obligation for him to uphold it.

Texas senator and Republican presidential candidate Ted Cruz has momentum heading into Tuesday's debate in Las Vegas. The Post's Katie Zezima explains his strategy and what happens next for him. (Gillian Brockell/The Washington Post)

The agreement doesn't include any penalties against countries that don't establish greenhouse gas emission limits, except for the largest and most obvious one. "The main penalty for non-compliance with the Paris agreement," Burger said, "is the continuing and increased risk of ecological catastrophe associated with climate change. That's a real incentive for climate change here. There are no trade sanctions. There are no civil penalties." There is simply a warmer, more unpredictable world.

In a poll released on the same day as the climate accord was approved, Bloomberg and the Des Moines Register revealed that 57 percent of Republicans in Iowa think that climate change is a hoax, making that less of a disincentive for someone like a President Ted Cruz. Stepping away from the Paris agreement would be a much easier way to demonstrate to the Republican base that he opposes climate action than, say, trying to unravel Obama's administrative actions on climate change which would generally require the same bureaucratic process under which they were adopted. If Cruz wanted to undo the Clean Power Plan, Burger said, it is "far more legally complicated. They'll have to go through notice-and-comment rulemaking. They'll have to show that the decision is not arbitrary and capricious. They'll have to show that the decision is a reasonable one." That's a much higher bar.

In March, we noted that Obama's legacy on climate change may end up being the achievement that is most at risk under his successor. The Paris agreement is a landmark for its inclusion of developing countries within its framework. But, as with nearly everything in climate politics, it may end up falling victim to partisanship.