The United States and China will both sign the Paris Agreement on climate change as soon as they can in April, a major step toward ensuring the international accord takes effect by 2020.

The two countries make up the world's top two sources of carbon emissions, and account for 40 percent of the globe's carbon dioxide emissions. Having the U.S. and China both sign the agreement would go a long way toward satisfying one of the conditions for the agreement to take effect: 55 countries and nations making accounting for 55 percent of global carbon dioxide emissions must approve the agreement domestically by Jan. 1, 2020.

Brian Deese, senior advisor to President Obama, said the announcement that both countries plan to sign the agreement on April 22, the first day the agreement can be signed, would signal to other countries that it's time to get on board.

"Our hope is that as the process proceeds, you will see growing momentum toward having that agreement come into force ... swiftly, on its own terms," he said.

The Paris Agreement was completed in December and saw 196 countries from around the world come together to try to limit global temperature rise below 2 degrees Celsius. Each country came up with its own plan to reduce their greenhouse gas emission, but the commitments are not legally binding and critics say the deal lacks teeth.

The Paris Agreement also contains commitments from rich countries to send money to poorer countries so they can develop more clean energy sources. Those financial commitments are also not legally binding.

The countries agreed to meet every five years to reassess their greenhouse gas reduction commitments with an eye toward ramping up the reductions, if possible.

Todd Stern, the Obama administration's top climate diplomat, said the agreement between China and the United States to sign the deal quickly might lead to the agreement going into effect quicker than anticipated.

"It precisely has the effect of leading to, potentially, an earlier entry into force," he said.

The White House hailed the agreement between Obama and Chinese President Xi Jinping as another step in a relationship that increasingly focuses on fighting climate change.

Xi and Obama first announced an agreement to work together on climate change policy in December 2014, and followed that up with further partnership pacts during Xi's trip to Washington, D.C., in September.

The two leaders also committed to pushing more climate-related international agreements in 2016. The top agenda items are reducing hydrofluorocarbons, or HFCs, and limiting greenhouse gas emissions from airplanes, according to a White House statement.

Stern said action on climate change becomes ever more urgent, especially with recent reports that a massive ice shelf in western Antarctica is melting faster than originally believed.

"The climate situation is serious, as we know. I think there is going to be ongoing evidence from the natural world of what we know and action on climate change is critical," he said.