This story has been updated.

PARIS — The gravity of the ongoing Paris climate talks grew Monday, as high-level country ministers took up a still heavily bracketed draft agreement text and began trying to find common ground in key remaining areas of contention.

“This is the week that everyone has been waiting for for years,” said Jennifer Morgan, head of the climate program at the World Resources Institute. “It’s when the decisions finally have to be made.”

The Paris climate meeting began last week with strong statements by heads of state, like President Obama, and a flurry of impressive announcements, including a commitment by African nations to install a dramatic 300 gigawatts of clean-energy capacity by 2030.

Then, these leaders departed and professional negotiating teams began working on a draft agreement, ultimately producing a document released Friday that narrowed down the options but still leaves crucial matters unresolved.

Those include whether the world will set a target of holding global average temperatures to “below 1.5 °C” or “well below 2 °C” above pre-industrial temperatures, and whether it will also adopt a very ambitious long-term goal, such as taking all carbon dioxide emissions to zero by 2060-2080, or settle for something less bold like steady “decarbonization” or ultimate “climate neutrality” in how we get energy.

Other key outstanding matters involve precisely how much money wealthier countries will contribute to helping developing nations both weather climate change and finance clean energy transitions. The agreement will also still have to resolve how often countries’ pledges to reduce their emissions will be reassessed and strengthened, and how progress towards these goals will be measured.

“There are some very tough issues here still,” said Alden Meyer, director of strategy and policy at the Union of Concerned Scientists.

Watch: The Paris climate change talks, explained in two minutes. (Gillian Brockell/The Washington Post)

There is general agreement that current country-level commitments heading into Paris are not strong enough to achieve the 2 degree Celsius target, and also that these commitments — many of which were just announced in 2015 — will not be strengthened further in this particular negotiation. Rather, a key goal of the agreement is to put in place a mechanism to ensure that ambition steadily increases over time and fast enough that all chances of limiting warming to that key level will not be lost.

Despite these challenges, observers said there is an overwhelming sense that some type of agreement will indeed be reached. Its strength is another matter.

“After the first week of negotiations, the mood is cautiously hopeful,” said Katharine Hayhoe, a climate scientist at Texas Tech University who was in Paris for the talks. “While key details of equity, finance and carbon accounting remain to be resolved, there is general agreement on the need for global agreement on how to reduce emissions and compensate those suffering the worst of the impacts.”

Negotiations are now being led by the host nation, France. President of the meeting Laurent Fabius, France’s foreign minister, called this the “week of hope” in a speech here on Monday. Fabius has  created pairings of key country ministers in order to hammer out the text in particularly difficult areas. He has said that by Thursday “at the latest” there will have to be a more “concrete” text. The final day of the conference is Friday, but matters could certainly continue past then.

“Those of you who have been with us a while know that if you want to make God laugh, just make a plan,” said Christiana Figueres, the executive secretary of the United Nations’ Framework Convention on Climate Change (under which this agreement will be adopted), at a news conference on Monday.

The draft agreement for the meeting has certainly gotten significantly less gnarled and peppered with notorious brackets, according to a statistical analysis by John Niles, a lecturer at the University of California at San Diego, and his colleagues at the website The conference began with a text that contained 1,035 open brackets and now has one that only has 567, their research found.

But a final agreement needs to have zero.

Meanwhile, significant divides persist over the strength of future climate targets and over financing future climate adaptation and clean energy transitions.

Extremely vulnerable nations, such as low-lying small island states, want the strongest temperature target (1.5 C) and very ambitious carbon cutting goals. However, the U.S. and China, two of the most influential parties in the debate, have generally lined up behind a goal of 2 C, not 1.5. In September the two countries jointly released a statement that twice cited the “below 2 degree C global temperature goal.”

Another critical area of dispute involves finance. In the 2009 Copenhagen accord, wealthy developed nations pledged to deliver $100 billion by the year 2020 “to address the needs of developing countries.” But it’s not clear when that $100 billion goal will be reached, or for that matter, what will happen after that.

At the same time, it is growing apparent that some nations not traditionally classified with the developed countries  in the context of these negotiations are nonetheless still fairly wealthy on a per-capita basis. So one question is whether such countries might also be expected to give money for climate finance.

“Many developed countries, not just the U.S., but the E.U., Australia, have said that if you’re an emerging developing economy and are in the position to give finance you should do so,” said Heather Coleman, who heads climate policy for OXFAM America.

The continuing divides underscore the cacophony inherent when close to 200 countries try to agree on momentous changes including how they will get their energy, and how they will develop.

A recurrent theme in this round of negotiations, as in previous ones, has been the gap between the relatively wealthy developed countries that have been responsible for the majority of historical greenhouse gas emissions, and developing nations that generally have not but may suffer some of the worst impacts of climate change.

One striking development, however, has been the large volume of sentiment in favor of trying to hold the planet’s warming to well below 2 degrees Celsius or even below 1.5 degrees Celsius.

One hundred and eight countries have now supported the 1.5-degree C temperature target, according to the Climate Vulnerable Forum, led by vulnerable small island nations. The current negotiating text’s language, with the two options of “below 1.5 °C” and “well below 2 °C,” hints at that shift.

Todd Stern, the U.S.’s special envoy for climate change, acknowledged at a press conference Monday that the U.S. would be okay with some reference to 1.5 degrees Celsius in a final agreement.

“The goal is to hold temperatures as far as possible below 2 degrees, but we are working with other countries on some formulation that would include reference to the 1.5 degrees, all as part of a somewhat broader sentence,” Stern said.

However, the Union of Concerned Scientists’ Meyer suggests it is important not to let the symbolism over 1.5 degrees get in the way of the more substantive mechanics of an agreement. “Giving a nod to 1.5 but then destroying the guts of the system that will actually help you get 2 is not the way we need to proceed,” he said.

Whether either one of these options is attainable remains to be seen. The countries’ current pledges, on their own, would only hold warming to 2.7 degrees C or worse, according to a variety of assessments by the U.N.’s Framework Convention on Climate Change and other parties.

Meanwhile, the complicated and bracketed negotiations can seem difficult to follow or understand, but it is really the sum of everything happening in Paris — including both the final text and also all of the mobilizations of clean energy plans and financing announcements —  that will ultimately determine whether the planet is getting on a better, safer climate path. And in this, the text of the agreement is quite crucial.

“The substance will make a big difference for whether you can say at the end, whether 2 degrees is in sight or not,” says the World Resources Institute’s Morgan.

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