As negotiations for a new worldwide climate agreement move into high gear, the attention is focused not just on how ambitious the treaty’s goals will be, but how urgently the world’s nations will act to make them come true.

The voluntary emission-cutting pledges that more than 180 countries brought to Paris do not offer deep enough reductions to guarantee a safe climate. So many negotiators, supported by climate campaigners, are now trying to get everybody to ratchet up their pledges as soon as possible.

Some nations, including the United States, would like the reviews and revisions to come fast on the heels of Paris and repeat every five years. Others, said to include China and India, are not so eager.

Todd Stern, the top American negotiator, said at a news conference Monday that there is “a large coalition for high ambition” that favored five-year detailed reviews of national pledges.

The reduction formulas would not themselves be legally binding because each nation crafts its own. But the process of reviewing and improving them would be strict, and making it transparent would require rigorous provisions written into the treaty, he said.

Until now, the most common denominator of the treaty’s ambition is whether it aims to keep temperatures from rising more than 2 degrees Celsius – or whether the limit should be set lower, perhaps as low as 1.5 degrees C.

But either target requires very fast action, one expert after another warned on Monday.

As the final week of talks began, senior ministers from around the world arrived for the final few days of negotiations, while their minions continued to work over the fine print.

In the back rooms, observers said the negotiators were focusing on whether the legally binding portion of the treaty should require countries to come back and revisit their commitments as soon as possible – maybe in 2018 or 2020, and preferably well before 2025 or 2030.

“Whether we can move toward decarbonization in time to stay below the 2 degree window,” said Christiana Figueres, who runs the United Nations climate apparatus, “remains to be seen.”

But Ban Ki-moon, the UN Secretary General, made plain that he wanted quick action.

“We cannot afford half measures and delay,” he said.

Other issues remain in play, notably how generous the rich countries would be in promising aid to the poorer ones in the years after 2020, when the new treaty takes effect.

All the questions are related, and some answers are being held back for last-minute horse trading. These include whether the treaty would set a long-term target of zero emissions of greenhouse gases, and when that should happen; how much money would be devoted to reducing emissions, and what share would go to adapting to a more dangerous climate.

Green groups and sympathetic corporations both said it would be important to review the emissions pledges sooner rather than later. Otherwise, the world might be left with a toothless treaty.

“Countries here who are questioning the need for an early review and ratcheting of their pledges are risking a 3-degree world,” said Mohamed Adow of Christian Aid. “That is a dangerous game.”

“Given the rapid changes in technology, science and policy, and the need to cut emissions further, the world needs to return to the table five years from now, in 2020, not wait 10 years to increase their efforts,” Jennifer Morgan of the World Resources Institute wrote in a blog posting.

“Five years is a long time in the business world,” said a similar statement from the We Mean Business coalition, which represents leading corporations and investors pushing for a robust treaty.

“For businesses and investors, 10 years is an eternity,” the group said. “If governments update the policy environment 10 years after Paris, their progress will lag behind that of businesses and investors, slowing the acceleration of finance and technology towards the low-carbon economy. It will also become unclear how the world can be brought onto a 2°C pathway, exposing everyone to the substantial additional risks of an even warmer world.”

Martin Kaiser of Greenpeace Germany called Ban’s formula for a five-year review cycle beginning immediately “precisely what we need.”

But he said the reviews are “not only to take stock – it needs to be translated into action.” Otherwise, he said, the inadequate pledges made so far would be written in stone.

One prominent scientist, Michael Oppenheimer of Princeton, pointed out that nobody knows how quickly new technologies will arrive and that’s another reason for periodic reviews.

“We are in the middle of an energy revolution,” said Oppenheimer, who has many years of experience writing assessments of science and policy for the UN. “No one knows how far it will go, or how fast.”