On Saturday, the U.S. and China, two of the world’s biggest polluters, formally joined the Paris Agreement during a ceremony in Hangzhou, China, ahead of the G-20 summit. President Barack Obama and President Xi Jinping deposited each country’s official instrument to join the agreement with U.N. Secretary General Ban Ki-moon.

The Paris Agreement was the result of last year’s U.N. Climate Change Conference (COP21), and the White House declared it the “most ambitious” climate change deal in history. More than 190 countries decided to adopt the agreement, which sets a goal of limiting a global warming increase to “well below” 2 degrees C. It will require participating countries to devise and maintain national climate plans to curb emissions, which could include the development of, and investment in, more renewable energy.

On Earth Day earlier this year, world leaders met in New York to reiterate their countries’ commitment to the Paris Agreement; however, that event was just the next step toward full implementation. As a White House announcement explains, in order for the Paris Agreement to take effect and enter into force, at least 55 countries representing at least 55% of global emissions need to ratify it.

Now that the U.S. and China, which are responsible for almost 40% of global emissions, have ratified the agreement and over 55 countries have already joined or publicly committed to work toward joining it this year, the White House says the Paris Agreement could enter into force by as early as the end of this year. In a statement, the Sierra Club says that timeline is “far earlier than many thought possible.”

In addition, the White House says both the U.S. and China have stated their intention to prepare and publish their respective mid-century, long-term low greenhouse-gas emission development strategies under the Paris Agreement. The U.S. has previously committed to publishing its strategy this year, and on Saturday, China committed to prepare its strategy as soon as possible. The two countries also announced that they will engage in technical collaboration and consultation on their strategies, the White House adds.

“We have a saying in America – that you need to put your money where your mouth is. And when it comes to combating climate change, that’s what we’re doing, both the United States and China,” said Obama on Saturday. “We’re leading by example. As the world’s two largest economies and two largest emitters, our entrance into this agreement continues the momentum of Paris and should give the rest of the world confidence – whether developed or developing countries – that a low-carbon future is where the world is heading.”

The president also noted that the efforts between the U.S. and China highlighted the importance of collaboration.

“[D]espite our differences on other issues, we hope that our willingness to work together on this issue will inspire greater ambition and greater action around the world,” stated Obama. “Yes, diplomacy can be difficult, and progress on the world stage can be slow. But together, we’re proving that it is possible.

Michael Brune, executive director of Sierra Club, applauded the U.S. and China. In a statement, he said their commitments “set a global precedent that has catapulted the world to the cusp of formally implementing the Paris Agreement and will have major positive implications for generations to come.”