The closing week of COP21 will be defined by how—and whether—parties can agree to frame the final document around these three crucial words.

Indigenous activists from South America paddle on kayaks during a rally in Paris on December 6, 2015. (Photo: Lionel Bonaventure/AFP/Getty Images)

At climate talks on the outskirts of Paris, so much depends on words. Over the weekend, negotiators released their newest draft of the United Nations climate accord, and the most celebrated bit of news was the elimination of pages and brackets. The document is now slimmed from 50 pages to a more readable 21 pages—a significant improvement over the unwieldy document produced in the first week of the Copenhagen talks in 2009, negotiators were quick to note—and more than 1,600 brackets were winnowed to just over 900. (That’s still a lot of brackets!)

The brackets are of utmost importance because they represent disputed terms, and chief among these is framing around the word "differentiation." That might sound wonky, but its meaning is surprisingly simple: On matters of finance, different countries should be treated differently, according to their capacities and vulnerabilities. In the context of the 1992 treaty that provides the framework for the climate negotiations, there are only two tiers of differentiation: developed and developing countries, with the former expected to give money to the latter to help them mitigate their emissions and adapt to climate change. One of the chief debates at this year's global climate talks centers around which countries should be included in which group.

"In the real world, the wall between developed and developing countries on finance is already breaking down," says World Wildlife Fund's Lou Leonard. China was considered a developing country in the original 1992 agreement, for instance, but now that China is the world's largest emitter, that categorization is a profound oversimplification. Saudi Arabia, which now has one of the world's highest GDPs, also remains classified as a developing country.

If the semantic debate sounds frivolous, it's worth remembering that such subtle differences in language could well make or break countries' ability to reach an agreement.

A handful of of the countries designated as "developing" under the agreement have already pledged money to the Green Climate Fund, which helps poor countries fight climate change. In fact, China, which announced earlier this fall that it would contribute $3.1 billion, might even surpass the United States in its contribution. (The U.S. has pledged $3 billion to the fund but faces opposition in Congress).

"The question now is whether the disappearance of that distinction [between developing and developed countries] will be enshrined in the new agreement, or whether that will remain something that just happens in the real world and will progress more over time," Leonard adds. "In the real world, it's already changed."

Meanwhile developed countries like the U.S. are keen to expand the pool of countries required to provide finance, from the small group of wealthy nations stipulated under the 1992 treaty—which includes the U.S., European Union members, Japan, and Australia, among a handful of others—to a far more encompassing arrangement.

And that brings us to a second important language gripe, which is that these developed countries would like to see language around who's expected to contribute expanded from "countries ready to do so" or "countries willing to do so" to "countries in a position to do so." (OK, this is technically an entire clause, but the shorthand is a single word: "potodoso"—short for "positioned to do so.") If potodoso appears in the final agreement, it would put the biggest developing economies, like China and Brazil, into the pool along with the U.S. et al. when it comes to helping poor countries.

If the entire debate around potodoso seems frivolous, it's worth remembering that such subtle differences in language could well make or break countries' ability to reach an agreement.

From a global perspective, the more countries that contribute to a climate change fund, the better. But rich developing countries want to be persuaded that they're not just taking care of developed countries, but instead complementing actions that those developing countries will undertake themselves. And that—as Steve Herz, the Sierra Club's senior attorney for the International Climate Program, tells me—is another way in which this week’s debates will really hinge on differentiation.

"In terms of finance, the big differentiation question is how do you define who has obligations to contribute and who else is encouraged to contribute," he says, adding: "You need to find some language in the middle that recognizes the existing obligations of developed countries, but also ensures countries who've become rich over time will also contribute."

Then there have been arguments around what to call the money given to developing countries, with some ambassadors and advocates taking issue with words like "charity," "aid," and "developmental assistance"—their argument being that such terms make “aid” sound both condescending and optional. "We don't want to hear 'compensation,'" LDC Watch's Prerna Bomzan has said. "It's reparations: reparations for climate debt."

Another one of the most-hyped words in the agreement is the verb "shall," which is legally binding in ways that “should” is not. It follows that poorer developing countries want lots of "shalls" in the financial section of the agreement, while richer developed countries prefer the softer language of "should." This particular linguistic distinction could have special weight in the U.S., where Congress controls questions of the purse and Republicans are eager to undermine Obama's authority on climate.

Then there are abuses against metaphor (though these are mercifully absent from the agreement itself). Cooking is a recurring one: Chinese negotiator Su Wei, for instance, recently compared the coming week at climate negotiations to preparing a good meal: “Everything must be there before you can make your meal. It’s the elements of Parisian cuisine. We have many ingredients, and we will emerge with a good meal.”

The next week will be defined by how, and whether, parties can agree to frame the final document around these three crucial words. The awkward metaphors are less divisive—nobody really takes issue them, except maybe journalists.

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