The United Nations is warning that an agreement in Paris next month won't be enough to curb the effects of climate change without steeper commitments from countries on emissions reductions.

"It is a very good step ... but it is not enough," said U.N. Climate Change Secretariat Christiana Figueres in a presentation given in Bonn, Germany, on Friday. She was presenting the findings of a U.N. report on all countries' commitments to carbon emissions reductions submitted to the U.N. to date.

Based on the commitments from more than 150 nations, the temperature of the Earth will rise by 2.7 degrees. Climate scientists say a rise of 2 degrees will be devastating to the Earth's climate. That creates the latest challenge for the climate change conference that begins Nov. 30 to get countries to make more commitments to reduce emission and cut fossil fuel use.

It is not certain how much more the U.S. can commit. President Obama has made reaching a deal in Paris a priority before his tenure ends in 2017 and has been rolling out a new clean energy effort almost weekly. Friday's report, however, could mean his goal of securing a global climate deal just got more difficult.

Figueres said big greenhouse gas emitters such as China will have to do more. "Many countries have been healthily conservative about what they have put forward," she said. She suggested that any deal made in Paris will have to include ways of changing targets and reduction goals several times as the agreement goes into effect. Many climate scientists blame greenhouse gases, mainly from burning fossil fuels, for driving manmade global warming.

Activist groups watching the climate discussions are remaining optimistic despite the new challenges.

"This is significant progress compared to just several months ago, when it seemed as if a 4° Celsius or more temperature increase was on the horizon," said Gustavo Silva-Chávez, climate change expert for the activist group Forest Trends, who will be participating in the Paris talks. Since then, countries have submitted required plans to the U.N. with commitments to emission reductions that brought down temperature projections down by 1.3 degrees, he said, reacting to the Friday's news.

"The commitments made by over 150 countries get us in the ballpark of what we need to keep global temperatures at acceptable levels — but they don't give us the home run we need," he said.

He says the challenge for Paris will be the 0.7-degree "gap," making sure commitments don't allow the Earth's temperature to increase more than 2 degrees by next century.

"According to many climate scientists, any increase above 2 C degrees will cause severe, irreversible climate impacts," he said. "However, closing this 0.7 C degree gap is within reach and something that the final negotiations in Paris can potentially achieve."

The Washington-based group World Resources Institute put out a statement prodding countries to do more, and do it soon.

"Despite the unprecedented level of effort, this [U.N.] report finds that current commitments are not yet sufficient to meet what the world needs," said Jennifer Morgan, the group's global director. "Countries must accelerate their efforts after the Paris summit in order to stave off climate change. The global climate agreement should include a clear mandate for countries to ramp up their commitments and set a long-term signal to phase out emissions as soon as possible."