“I’m very comfortable with the word ‘revolution,’ ” Figueres said. Illustration by Ben Wiseman

The United Nations Framework Convention on Climate Change, or U.N.F.C.C.C., has by now been ratified by a hundred and ninety-five countries, which, depending on how you count, represents either all the countries in the world or all the countries and then some. Every year, the treaty stipulates, the signatories have to hold a meeting—a gathering that’s known as a COP, short for Conference of the Parties. The third COP produced the Kyoto Protocol, which, in turn, gave rise to another mandatory gathering, a MOP, or Meeting of the Parties. The seventeenth COP, which coincided with the seventh MOP, took place in South Africa. There it was decided that the work of previous COPs and MOPs had been inadequate, and a new group was formed—the Ad Hoc Working Group on the Durban Platform for Enhanced Action, usually referred to as the A.D.P. The A.D.P. subsequently split into A.D.P.-1 and A.D.P.-2, each of which held meetings of its own. The purpose of the U.N.F.C.C.C. and of the many negotiating sessions and working groups and protocols it has spun off over the years is to prevent “dangerous anthropogenic interference with the climate system.” In climate circles, this is usually shortened to D.A.I. In plain English, it means global collapse.

The Framework Convention on Climate Change is overseen by an organization known as the Secretariat, which is led by a Costa Rican named Christiana Figueres. Figueres is five feet tall, with short brown hair and strikingly different-colored eyes—one blue and one hazel. In contrast to most diplomats, who cultivate an air of professional reserve, Figueres is emotive to the point of disarming—“a mini-volcano” is how one of her aides described her to me. She laughs frequently—a hearty, ha-ha-ha chortle—and weeps almost as often. “I walk around with Kleenex,” another aide told me.

Figueres, who is fifty-nine, is an avid runner—the first time I met her, she was hobbling around with blisters acquired from a half marathon—and an uninhibited dancer. Last fall, when her office was preparing for the twentieth COP, which was held in Lima, she and some of her assistants secretly practiced a routine set to Beyoncé’s “Move Your Body.” At a meeting of the Secretariat staff, which numbers more than five hundred, they ripped off their jackets and started to jump, jump, jump.

Figueres works out of a spacious office in Bonn, in a building that used to belong to the German parliament. On the wall by her desk there’s a framed motto that reads, “Impossible is not a fact, it is an attitude.” On another wall there’s a poster showing the Statue of Liberty waist-high in water, and on a third a black-and-white photograph of Figueres’s father, José, who led the Costa Rican revolution of 1948. He served as President of the country three times, pushed through sweeping political and social reforms, and abolished Costa Rica’s army as a stay against dictatorship. Figueres grew up partly in the President’s House and partly on her father’s farm, which he called La Lucha sin Fin—“the struggle without end.”

“I’m very comfortable with the word ‘revolution,’ ” Figueres told me. “In my experience, revolutions have been very positive.”

Of all the jobs in the world, Figueres’s may possess the very highest ratio of responsibility (preventing global collapse) to authority (practically none). The role entails convincing a hundred and ninety-five countries—many of which rely on selling fossil fuels for their national income and almost all of which depend on burning them for the bulk of their energy—that giving up such fuels is a good idea. When Figueres took over the Secretariat, in 2010, there were lots of people who thought the job so thankless that it ought to be abolished. This was in the aftermath of the fifteenth COP, held in Copenhagen, which had been expected to yield a historic agreement but ended in anger and recrimination.

Figueres and her team have spent the years since Copenhagen trying to learn from its mistakes. How well they have done so will become apparent three months from now, when world leaders meet for this year’s COP—the twenty-first—in Paris. Like Copenhagen, Paris is being billed as a historic event—“our last hope,” in the words of Fatih Birol, the incoming director of the International Energy Agency—and, again, expectations are running high. “We are duty-bound to succeed,” France’s President, François Hollande, has declared.

The danger of high expectations, of course, is that they can be all the more devastatingly dashed. Figueres, who is well aware of this, is doing her best to raise them further, on the theory that the best way to make something happen is to convince people that it is going to happen. “I have not met a single human being who’s motivated by bad news,” she told me. “Not a single human being.”

To understand how the fate of the planet came to be entrusted to a corps of mostly anonymous, mid-level diplomats, you have to go back to the nineteen-eighties, when the world confronted its first atmospheric crisis. That crisis, the so-called ozone hole, was the product of chemicals known as chlorofluorocarbons, or CFCs. When they were invented, in the nineteen-twenties, CFCs were hailed as miracle compounds—safe alternatives to the toxic gases used as early refrigerants. Lots of additional uses were found for CFCs before it was discovered that the chemicals had the nasty effect of breaking down stratospheric ozone, which protects the earth from ultraviolet radiation. (F. Sherwood Rowland, a chemist who shared a Nobel Prize for this discovery, once reportedly came home from his lab and told his wife, “The work is going well, but it looks like it might be the end of the world.”) A global treaty—the Vienna Convention for the Protection of the Ozone Layer—was signed in 1985 and sent to the U.S. Senate by President Ronald Reagan, who called for its “expeditious ratification.” This broadly worded “framework” was soon followed by the Montreal Protocol, which called for drastic cuts in CFC usage.

The Montreal Protocol, which has been revised a half-dozen times, mainly in response to new scientific data, averted a dystopian future filled with skin cancer and cataracts. (If you’re sitting in the sun right now, in a roundabout way you can thank the Montreal Protocol.) Kofi Annan, the former Secretary-General of the U.N., has labelled it “perhaps the single most successful international agreement to date.”

When scientists first sounded the alarm about carbon emissions, it seemed logical to try to follow the Montreal template. In 1988, the U.N. General Assembly adopted a resolution declaring climate change to be a “common concern of mankind.” The following year, talks began on what was to become the Framework Convention.

The ozone treaty had divided the world into two blocs: high CFC users, like the United States, and low users, like Bangladesh. High users, who were largely responsible for the problem, were expected to act first, low users later. The same high-low distinction held for climate change; some countries had contributed a great deal to the problem, others very little. But almost immediately the blocs fractured into sub-blocs. Oil-producing states, like Saudi Arabia, split with low-lying, easily inundated nations, like Maldives. Rapidly industrializing countries, like India, saw their interests as very different from those of what are officially known as Least Developed Countries, like Ethiopia. The European Union wanted a treaty with strict targets and timetables for reducing carbon emissions. The United States—at that point the world’s largest emitter—refused even to consider such targets. On the eve of what was supposed to be the final negotiating session on the Framework Convention, the working draft of the document, according to one participant, resembled a “compilation of contradictory positions more than a recognizable legal instrument.”