President Obama on Saturday joined the United States into the Paris climate change agreement, bringing the landmark pact significantly closer to taking effect worldwide.

Obama agreed to the international deal along with Chinese President Xi Jinping in China, continuing the cooperation on major climate actions over the last two years by the leaders of the world’s two largest economies and greenhouse gas emitters.

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The two countries signed documents committing them to the deal, and then turned those documents over to United Nations Secretary General Ban Ki-Moon, according to the White House.

The action of joining the United Nations deal is equivalent to ratifying it. But Obama fought to ensure that the agreement, reached in December in Paris, is not a treaty and does not require the approval of two-thirds of the Senate, as treaties do.

The deal asks countries to reduce their greenhouse gas emissions by amounts chosen by their governments. Even once it takes effect, the emissions cuts prescribed in the deal are non-binding, but it does require countries to report their emissions to the UN’s climate oversight board.

Implementing the deal quickly has practical political implications in the United States.

White House officials said the announcement will send a signal to the world that both countries are serious about implementing the Paris deal.

“The signal of the two largest emitters, and the two largest economies, taking this step together and taking it early, should give confidence to the global community and to other countries that are working on their climate change plans, that they, too, can move quickly and be part of a global effort to do that,” Brian Deese, President Obama’s top climate change adviser, told reporters Friday in previewing the action.

Under the agreement, the United States will cut its emissions by 26 percent to 28 percent, from 2005 levels, by 2025. China has committed to seeing its emissions peak by 2030, but reducing its ratio of emissions to economic activity over that time.

With the U.S. and China formally entering into the pact, it now has the support of 25 nations representing just over 39 percent of the world’s greenhouse gas emissions, according to the World Resources Institute.

The two countries are the world’s largest emitters, with the United States accounting for 17.9 percent of gases and another 20.1 percent coming from China.

Few other major nations have joined the deal, though more than enough have committed to doing so. France in June voted to ratify the agreement, but the European Union must join it together.

Once 55 nations representing 55 percent of the world’s greenhouse gas emissions enter into the agreement, it takes effect. A report from the Marshall Islands predicted last month that the agreement would reach that threshold by the end of the year, based on commitments that leaders have made.

With the U.S. and China joining the deal, “you can see a very clear and credible path toward the paris agreement entering into force in 2016,” Deese said.

Republicans and the fossil fuel industry have roundly criticized agreement and questioned its effectiveness, especially given its acceptance of emissions growth from emerging economies like China and India.

Critics say the deal will hamstring the American economy, raise energy prices and drive American jobs overseas.

Republicans have looked to block implementation of the deal. Since it’s non-binding, though, the Senate wasn’t required to ratify the plan before the U.S. could formally join it, meaning lawmakers have little recourse against the deal.

She supports the Paris deal, and during climate-related campaign speeches, often highlights her work on climate change while she was Obama’s secretary of State.

Trump has been hostile to the deal, threatening to cancel it if he’s elected president in November. If the deal were to take effect before he took office, he could not change the terms of the plan during his tenure. Since the deal is non-binding, however, he could still simply ignore the carbon reduction goals set by President Obama.

But even if Trump is elected, the Obama administration is confident that its promises on climate are durable.

“While there is obviously a very partisan political debate on this issue in some parts of the Republican Party, the debate among the business community ... is just not the same debate,” Deese said.

“That progress in the business community, in the private sector and internationally is going to ultimately pull the United States in the direction of progress, regardless of what happens going forward.”