Xi Jinping, China’s president, left, speaks during a joint news conference with U.S. President Barack Obama in the Rose Garden at the White House in Washington, D.C., U.S., on Friday, Sept. 25, 2015. (Pete Marovich/Bloomberg)

Against a backdrop of troubling news from the planet — including a scientific upgrade of expectations for sea level rise because of faster melting of Antarctica — the U.S. and China on Thursday pledged to jump-start their climate action plans.

The world’s two largest emitters issued a joint statement saying that they will sign the Paris climate agreement, negotiated late last year to put the world on a path to lowering greenhouse gas pollution, on April 22, the date of a long planned signing ceremony and the first day that countries can sign. April 22 is also Earth Day.

The U.S. and China further said they would “take their respective domestic steps in order to join the Agreement as early as possible this year” and called on other countries to do likewise, “with a view to bringing the Paris Agreement into force as early as possible.”

“Our two countries, with this joint statement, are making an important step forward in building on the success of Paris by urging and encouraging swift entry into force of that agreement,” said Brian Deese, senior adviser to the President, on a press call.

The Paris accord set a target of limiting the globe’s warming to “well below” 2 degrees Celsius above pre-industrial levels, and trying to hold warming to 1.5 degrees C if possible.

The news comes as the planet continues to set temperature records regularly. January exceeded the 1951-1980 average by 1.13 degrees C, according to NASA, and February exceeded it by 1.35 degrees C.

Meanwhile, the combination of climate warming and El Nino has triggered severe bleaching of parts of the iconic Great Barrier Reef, and the threat of rising seas — the major concern of the bloc of small island nations that drove urgency in the Paris agreement — looks a lot worse in a new computer modeling study. The research found that with unchecked emissions, Antarctica could double currently expected sea level rise by 2100, from around 1 meter at the high end to closer to 2 (over 6 feet).

The new statement by the U.S. and China does not refer to any particular scientific or atmospheric developments. Asked on a press call about how the climate system is currently behaving, Todd Stern, the State Department’s special envoy for climate change and the top negotiator for the country in Paris, responded that “Paris gives us a chance. Paris puts us on the right path, with the right structures built into it, but there’s no time to lose. We know that. And the evidence from the natural world keeps telling us that louder and louder.”

The Paris agreement does not come into force until 2020, and there has long been concern about what happens in the period between now and then. It also requires 55 separate countries, which in turn represent 55 percent of global emissions, to sign and ratify the document for it to come into effect. “Joining the Paris Agreement follows a two-step process: countries must sign the Agreement, and then also indicate their consent to join and be bound by it as Parties,” explains the World Resources Institute.

Hence, the early signal from the U.S. and China is significant — if these huge emitters are taking swift implementation actions, then it will be easier to hit the required threshold. However, the U.S.’s actual ability to cut emissions also depends in part upon the administration’s Clean Power Plan, which was stayed by the U.S. Supreme Court and currently remains in legal limbo. On the press call, Deese stated that the administration feels “very confident [the plan] is on strong legal foundations. It was always expected to be challenged in the courts.”

The Paris agreement, in effect, brings together independent country-level commitments to reduce emissions, rather than imposing any type of global cap. But numerous assessments have suggested that those individual national goals don’t add up to enough to hold warming below 2 degrees C. So the agreement envisions a “global stock-take” in which the world assesses how it is doing in trying to meet its climate goals, after which nations may, presumably, have to further increase their ambitions.

Read more at Energy & Environment:

What Florida’s ancient past tells us about sea level rise today

The enormous carbon footprint of food that we never even eat

A really bad winter for the Arctic just got even worse

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