A clause tucked away at the bottom of the draft agreement handed out at the Paris climate talks could blow up the agreement even if it is signed Saturday.

Article 18 Section 1 says the agreement will come into effect after at least 55 countries that have signed the agreement ratify, accept or approve the agreement domestically. But, crucially, for the agreement to take effect in 2020, countries that account for 55 percent or 70 percent — the percentage is still being negotiated — of global greenhouse gas emissions must be on board.

That means that if China, the United States, India, Russia, Japan or any of the other large emitters don't approve of the agreement domestically, the last two weeks could amount to nothing.

China is the world's biggest greenhouse gas emitter, accounting for about 28 percent of global emissions, according to federal statistics. If China or the U.S., which accounts for 16 percent, Russia, India, Japan or some of the major countries responsible for the remaining 40 percent of emissions can't approve the agreement, the deal could fall apart.

It remains to be seen what form that paragraph will take in the final draft that is expected to be released early Saturday morning. The 21st Conference of the Parties, or COP21, was scheduled to wrap up Friday, but French Foreign Minister Laurent Fabius announced that it would continue into Saturday.

The draft is expected to be discussed through Saturday morning with a final vote coming around midday Eastern time.

At least one environmental group in Paris is not concerned that the clause would lead to problems after the conference.

"The agreement would be reached by consensus and we fully expect every country to stand by the commitments that they make," said Steve Herz, an attorney with the Sierra Club's International Climate Program. "There's no reason to think that countries will not go home and approve it."

The State Department did not respond to a request for comment about the specific clause in the draft agreement and whether the U.S. delegation would seek to soften or eliminate the clause.

Depending on what legally binding language is included in the final agreement, the United States might be one of the countries facing an uphill climb to get the agreement ratified domestically.

As of the Thursday draft agreement, the U.S. delegation seemed to be getting its way by having much of the clauses in the agreement softened, making much of the participation in the agreement voluntary.

Reports from Paris indicated many developing countries that face direct threats from climate change were none too pleased by the U.S. insistence on softened language. Countries at the conference know that the Republican-controlled Senate would not ratify an agreement.

Andy Koenig, a senior policy adviser at Freedom Partners, a group partially funded by the Koch brothers, said Congress needs to find a way to stop the agreement.

"Lawmakers should reject the administration's attempt to bypass Congress for a symbolic deal that would do nothing but increase our debt and commit us to mandates that destroy our economy," he said.

That opposition means soft language in the document that has angered climate activists in Paris.

On Friday, White House spokesman Josh Earnest acknowledged the deal wouldn't be enough to mitigate the effects of climate change on its own.

He echoed the Obama administration's long-held stance that Paris needs to be the start of a long conversation about how to fight the effects of climate change, not the end-all-and-be-all of discussions.

"What we hope will be agreed to in Paris will ... not be sufficient to entirely solving the problem," Earnest said. "And that's why we believe a core component of the agreement should be a commitment on the part of the countries who are signing on the dotted line to review the commitments that they've made at a regular interval."