If every country meets the full extent of its pledge to cut greenhouse gas emissions, there will still be as much as 12 billion tons more climate change pollution in the atmosphere by 2030 than there should be to keep global temperatures at safe levels, the United Nations has estimated.

The U.N. Environment Programme's sixth annual "Emissions Gap Report" found the targets that countries have vowed to implement as part of an upcoming accord in Paris will still see global emissions rise to 54 billion tons in 2030. Scientists have said those levels should not exceed 2 billion tons if the world hopes to stay within the limit of 2 degrees Celsius above preindustrial temperatures.

UNEP Executive Director Achim Steiner said the fact that more than 150 countries have put forward climate plans is "unprecedented" and signals strong momentum for Paris.

"I do think it is important for the world to understand it is not simply the status quo scenario. We are beginning to bend the curve, but ... it is not yet enough," he said. "We are probably halfway to what we need to do to achieve on longer-term trajectory."

By the second half of the century, Steiner said, the world will have to reach a level of zero net emissions. He called for the Paris deal to include a "dynamic approach" that will demand that countries ramp up their targets on a regular basis.


Concerns about 'the ambition gap'

The UNEP report comes as ministers from 195 countries travel to Paris for two days of high-level climate discussions before the main negotiations kick off at the end of the month. Finding a way to close that gap will be a top order of business, according to a background note.

About 80 ministers will divide into four working groups to hash out some of the major issues ahead of Paris: ensuring poor countries will have money to cut emissions and adapt to climate change, boosting the measures that nations will take before 2020 to slash emissions, the deal's overall level of ambition and crafting something fair for countries of different levels of wealth and development.

"It's definitely getting ready for the big show," said Alden Meyer, director of policy and strategy for the Union of Concerned Scientists. "The ambition gap is definitely one of the issues that people are going to be talking about."

According to the background note prepared by the French hosts, ministers won't be negotiating a messy and bracket-heavy 55-page text that came out of the most recent U.N. talks. Rather, they said, they want ministers to "provide the necessary political guidance to the ... negotiating process and to come up with proposals for common ground on some of the key political issues that remain open."

Elliot Diringer, executive vice president of the Center for Climate and Energy Solutions, called the Nov. 8-10 meeting an opportunity for ministers to come to some agreements and instruct their negotiators to find compromises in Paris.

"Even if the text doesn't look like it has advanced, the conversation has advanced," Diringer said. "Now it's a chance to bring it back up to the political level and hopefully get some clear guidance to negotiators for the early days in Paris."

'Major' progress in HFC talks

U.S. leaders said one bright spot in the effort to close the emissions gap could come in the form of the Montreal Protocol on Substances that Deplete the Ozone Layer. Countries meeting in Dubai, United Arab Emirates, yesterday agreed to use that agreement to ratchet down hydrofluorocarbons (HFCs), powerful greenhouse gases, starting in 2016.

"This is a major accomplishment," Secretary of State John Kerry said in a statement. He noted that countries also pledged to "work toward" formally amending the protocol, saying doing so would avoid 0.5 C of warming by the end of the century.

"The progress in Dubai also indicates that the world is ready for a new chapter in the fight against climate change. In agreeing to address HFCs together, we have laid the groundwork for even greater cooperation toward a successful outcome in Paris," Kerry said.

That wasn't an easy agreement to get, and experts involved in the effort to reduce HFCs said the fight is far from over. Durwood Zaelke, founder of the Institute for Governance and Sustainable Development, noted that many countries -- including the United States and island nations -- wanted to move faster but were stymied by India and Persian Gulf oil-producing nations.

Those countries pushed to delay the details of the agreement until after Paris, Zaelke said, "raising a red flag about their tactics." Still, he noted, "if there is a silver lining to this slow deliberation, it is that parties will be able to implement a strict phase-down schedule much faster than usual."

He argued that phasing down HFCs will eliminate up to 100 billion tons of carbon dioxide equivalent by 2050. Meanwhile, the UNEP report notes that countries in their plans for Paris could be on track to slash 4 to 6 gigatons of greenhouse gases compared to business as usual.

"The potential for scaling up for greater enhanced ambition is not theoretical," Steiner said. "They are plentiful, but they will require continued concentration by countries individually and by the global community collectively to set the right policy signals."