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What a way to celebrate Earth Day.

A total of 155 nations, including the U.S. and China, are planning to sign the Paris Agreement on Climate Change on Friday, which is the first day it will be open for signature. 

Such a large number of signatories so quickly would set a record for international agreements, beating out the 119 signatories on the opening day of the U.N. Convention on the Law of the Sea in 1982. 

This massive single-day signing, the specifics of which were confirmed by the U.N. and a senior State Department official, would show the continued momentum behind taking action to curb manmade global warming.

“It clearly demonstrates the degree of support internationally for moving forward on climate."

“It clearly demonstrates the degree of support internationally for moving forward on climate," said David Waskow, the director of the international climate initiative at the World Resources Institute.

The event, which U.N. Secretary General Ban Ki-moon is coordinating, is likely to make it possible for the agreement to enter into force sooner than expected. 

When the agreement was negotiated in Paris in December, it was anticipated that it would enter into force in the 2018 to 2020 timeframe. 

The agreement for the first time commits all nations -- large and small -- to undertake actions to reduce global warming pollutants. Countries would, over time, make increasingly ambitious emissions cuts.

The agreement does not actually specify when it will enter into force. Instead, it contains a provision saying it will enter into force once 55 nations totaling at least 55 percent of global emissions join the agreement. 

But signing the agreement is different than joining it. Joining requires a legal process to play out within each country. Still, it's a sign that a relatively swift entry into force is likely.

“It's quite likely at this point that it will go into effect before 2020,” Waskow told Mashable.

According to a senior State Department official, the U.S. will jointhe agreement sometime this year, once a process plays out within the executive branch. 

The Obama administration does not see a need to submit the agreement to the Senate for approval, saying it falls under the 1992 U.N. Framework Convention on Climate Change, rather than as a new, formal treaty.   

President Obama and Chinese President Xi Jinping have each pledged to join the agreement during 2016 -- a move that is aimed at encouraging other countries to do so as well. 

Obama has made climate change a major focus of his second term, even traveling to Alaska to view rapidly melting glaciers firsthand.

"What I think we’re seeing is the standing ovation that was reached in Paris will now be translated into clear intent to deliver as countries sign on the bottom line," said Jake Schmidt of the Natural Resources Defense Council, in a statement.

Why the timing matters so much

The sooner the agreement enters into force, the sooner each country's pledges to cut emissions (technically known as Intended Nationally Determined Contributions, or INDCs) turn into national obligations. 

“When countries cross that point of deciding to join they are also deciding to fully commit” to their emissions targets, Waskow said.

In addition, an earlier start to emissions cuts could yield a more ambitious agreement down the road, which would be critical to actually meeting the goals of the treaty itself. 

The U.S. will work to reduce greenhouse gas emissions by 26 to 28 percent below 2005 levels by 2025.

In other words, the U.S. INDC says the country will work to reduce greenhouse gas emissions by 26 to 28 percent below 2005 levels by 2025. Once the country formally joins the agreement, that intent will turn into a more formal obligation.

The agreement calls for countries to keep manmade global warming to below 2 degrees Celsius, or 3.6 degrees Fahrenheit, above preindustrial levels by 2100, and to try to limit warming to 1.5 degrees Celsius, or 2.7 degrees Celsius, above preindustrial levels. 

However, for all its groundbreaking elements, the agreement is something of a paradox. Scientific assessments show that, once they're added together, the emissions pledges within the agreement don't go far enough to reach the temperature targets. 

A new analysis released on Wednesday by Climate Interactive and MIT found that countries will have to significantly strengthen their emissions pledges by 2030 in order to keep warming below the 2-degree target. 

The report finds that implementing the current pledges would put the world on course for 3.5 degrees Celsius, or 6.3 degrees Fahrenheit, of warming by the end of the century. 

The agreement itself contains what is known as a "ratchet mechanism" for countries to meet again every five years, beginning in 2020, to put forth more ambitious emissions cuts. 

The Climate Interactive study found that the longer that countries wait to ratchet up their commitments, the steeper the rate that they must cut emissions to meet the agreement's goal. If they wait too long, the emissions cuts required would be too steep to be feasible, making them all but impossible to achieve without some sort of new technological breakthrough.

A separate report, released by Climate Central on Wednesday, found that the global climate system is already flirting with the 1.5-degree Celsius temperature target, and echoes the call for more ambitious emissions cuts to be made in the next few decades. 

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