The United Nations says to expect a major push next week to ratify last year's Paris climate deal ahead of oral arguments in the court fight that could decide the fate of President Obama's climate change agenda.

The U.N. is expecting about 20 countries to send their ratification documents in the coming days, with Morocco, which is hosting the next round of meetings on the Paris deal in November, saying it plans to ratify the climate accord Wednesday.

Brazil, Mexico and other countries are also expected to ratify the deal during the special Wednesday ceremony at U.N. headquarters in New York during the week-long General Assembly.

"We are seeing many countries racing towards the finish line," said U.N. climate adviser Selwin Hart at a briefing Thursday afternoon. "We have made incredible progress to cross those thresholds ... It usually takes years, decades and sometimes never to cross these thresholds for entry into force."

David Nabarro, the top U.N. adviser on sustainability, called Wednesday's event the "most significant" moment of the General Assembly week. Nabarro is "absolutely certain" the Paris climate change agreement will enter into force before the end of 2016.

As of this week, 27 countries, including the U.S., China and Norway, have ratified the agreement. With next week's moves, it would be close to going into effect, but would be just shy of the 55 countries required, representing 55 percent of the world's emissions, to enter into full force.

At the same time, however, groups opposing the key regulation in meeting the United States' obligations will be preparing to go to court on Sept. 27.

It is not clear what would happen if the administration loses the case against the Environmental Protection Agency's Clean Power Plan or if it would make the U.S. ratification of the Paris accord moot. The court's decision may not come until next year.

The Obama administration is confident it will win the case. It also has advised federal judges that its climate rules should be upheld given the significance of the historic deal made in Paris.

The key climate regulation, called the Clean Power Plan, is the central ingredient in Obama's plan to meet the Paris agreement's goal of stopping the Earth's temperature from rising 2 degrees in the coming decades.

The plan requires states to reduce greenhouse gas emissions a third by 2030, which the 30 states opposing the plan call unconstitutional. Many scientists blame greenhouse gas emissions from burning fossil fuels for driving man-made climate change.

Critics also argue that the plan won't do much to reduce the effects of global warming, despite the president's continued promotion of the EPA's plan in setting the country on the path toward lower emissions.

The full D.C. Circuit Court of Appeals will hear the oral arguments. The lawsuit was brought by nearly 30 states and dozens of industry trade associations. The Republican Party has been adamantly against the regulations, referring to it as a central part in the EPA's broad agenda of regulatory overreach.

Congress has tried to stop it using a variety of legislative means. But without the necessary votes to overcome a presidential veto, those efforts have failed.