After weeks of negotiations diplomats in France unveiled a landmark deal to tackle climate change and reduce greenhouse gases. If adopted, the accord aims to limit the rise in global temperatures to less than two degrees Celsius. (Reuters)

This story has been updated.

LE BOURGET, France — The Paris climate-change conference was supposed to be about the needs of big countries and what they are willing to do to slow the warming of Earth’s atmosphere. But in the end, the two weeks of sometimes round-the-clock negotiations focused at least as much on some of the smallest, most defenseless nations whose very existence could hinge on the outcome of the talks.

The result, it now appears, could be a tougher set of policy goals than anyone originally thought could emerge from the conference. A newly released draft agreement, to be voted on Saturday, pledges the world to limit global warming to “well below 2 °C above pre-industrial levels,” but also to “pursue efforts” towards a far more challenging and aspirational goal to “limit the temperature increase to 1.5 °C.”

That tougher language might not be legally binding for countries such as the United States, but the fact that it appears in this latest text is testament to the tireless work of delegations from remote countries facing an urgent threat from the rising seas of a warmer Earth.

The growing momentum behind 1.5 degrees is a story of fast-breaking science, savvy politics and a change in tone in the climate debate — one that, pushed by Pope Francis, has focused increasing attention on the needs of the most vulnerable countries. (The Vatican on Thursday came out in favor of the 1.5-degree target.)

“The small guys have managed to push the big guys, and that is a big story,” Monica Araya, founder and executive director of the Costa Rican nongovernmental organization Nivela and special adviser to the Climate Vulnerable Forum, said at the conference Friday.

Early Saturday, French Foreign Minister Laurent Fabius announced that a proposed draft of the new climate agreement was ready for debate and possible approval by delegates of the 196 countries attending the talks. Fabius described the proposed agreement as “historic,” “ambitious and balanced,” providing a pathway that would allow countries to sharply reduce greenhouse-gas pollution and avoid a dangerous warming of the planet.

“Today we are close to the final outcome,” Fabius told the assembled delegates at a conference center in Paris’ northern outskirts. He called on diplomats to approve the  compromise reached by negotiators overnight, one that he said “affirms our objective … to have a temperature [increase] well below 2 degrees [Celsius] and to endeavor to limit that increase to  1.5 degrees, which should make it possible to reduce the risks and impacts linked to climate change.”

As he spoke the words, the conference hall erupted in applause.

“The world is holding its breath,” Fabius said.

Diplomats labored nonstop for the last 48 hours of the conference to resolve differences over a handful of thorny issues, including financial aid to developing countries hit hard by climate change, as well as rules and procedures for judging whether countries are honoring their commitments to cut pollution.

Secretary of State John F. Kerry, in Paris to help push for a deal, said Friday there had been “a lot of progress” but also a few snags during late-night bargaining.

“I’m hopeful,” he told reporters. “I think there is a way to go forward, that there’s a reasonableness.”

For many years, small island nations such as the Maldives — joined more recently by a broader group of climate-vulnerable countries in Africa, Asia and Latin America — have pushed to make the world recognize tougher climate goals. It has been a long-shot fight because of the massive effort required to meet even the less stringent goal of restricting warming to less than two degrees Celsius above preindustrial temperatures, and also because of their relative lack of political and economic power.

“Maldives itself has over 3,000 years of history,” said Ahmed Sareer, the Maldives’ permanent representative to the United Nations and its ambassador to the United States. “The location, the culture, the language, the traditions, the history, all this would be wiped off” if sea levels are allowed to rise high enough.

Nonetheless, holding warming to 1.5 degrees hardly seemed realistic. With the world already at about one degrees Celsius over preindustrial levels and current national emissions pledges well off target even for two degrees, how would 1.5 ever happen?

Still, small island nations brought their case to Paris. Their message was epitomized by a poster at the Wider Caribbean Pavilion at the vast Le Bourget conference center. The poster shows a young girl up to her neck in ocean water. Behind her, the now-submerged beach she’s standing on sports a drowned sign: “1.5 to stay alive,” it reads.

The talks in Paris were barely getting underway last week when representatives from Antigua and Barbuda made a series of impassioned pleas to the nations gathered to negotiate a climate treaty. In speeches and in a written appeal, officials from the islands warned that their homeland was literally in danger of being swept away by rising sea levels.

Even if all countries honored their current promises to cut greenhouse-gas emissions, global temperatures would rise by 2.7 degrees Celsius — and “that would be too much,” the delegation said, summarizing its view on its official Twitter account.

“The ministers came to the [talks] so that we might escape a world of plus-3 degrees, and for refusing to sign the death warrant of certain countries,” the message read. “It seems that this promise is forgotten.”

Antiguan officials delivered similar messages in closed meetings, warning that other island nations faced “an existential threat” unless the negotiators increased their ambition and sought even stricter emission controls to keep the temperature rise from exceeding 1.5 degrees, according to a diplomat present during the session. For these countries, the risks include not just the loss of land but the death of vital fisheries as more coral reefs die because of higher temperatures and increased acidity.

Similar appeals have been made for years, but in Paris the islanders acquired new allies: African nations, Europeans, even some Americans expressed sympathy, the diplomat said.

As the Paris meeting unfolded, the 1.5 target received more and more acknowledgment from major economies such as France, Canada and the United States. Then, a near-final draft agreement released Thursday enshrined it as the aspirational climate goal of the entire world. Countries, the draft said, will take steps to hold “the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C.”

The language was retained in a draft that was scheduled for debate and final approval on Saturday. Officials cautioned that changes could still be made in the talk’s final hours. “Nothing is agreed until everything is agreed,” Fabius said earlier in the week.

Still, observers say that the moral appeal of small-islanders has merged with a growing body of troubling science suggesting that their temperature target turns out to be a meaningful one.

It was not until 2008, at the Poznan climate meetings in Poland, that the coalition of small island nations called the Alliance of Small Island States formally stood up for the position of a 1.5-degree temperature target, said Bill Hare, a physicist and a founder of Climate Analytics. The group has conducted considerable research on the 1.5-degree target to help small island nations and developing countries.

But there was not much science at the time to differentiate 1.5 degrees from two degrees. Climate Analytics science director Michiel Schaeffer and scientific consultant Joeri Rogelj note that many climate studies have tended to compare impacts at two degrees with impacts at much higher temperature increases, rather than to suss out the differences between 1.5 and two, which turn out to be fairly substantial.

“There’s a significant difference between one and a half degrees and two degrees if you look at survival of coral reefs, and shifts in heat and precipitation extremes,” Schaeffer said, “and for example, a doubling of risk for food security at two degrees compared with one and a half degrees.”

And then, most of all, there is sea-level rise. Recent research suggests not only that every one degree of temperature increase (Celsius) will lead to about 2.3 meters of long-term sea-level rise (over seven feet), but that the long-term stability threshold of the Greenland ice sheet may also lie at around 1.5 degrees, or just above it. (The stability threshold of the West Antarctic ice sheet may already have been reached).

So even as small island states pushed more and more for 1.5 degrees — and as their coalition grew to include more developing countries — scientific research on ice-sheet vulnerability and sea-level rise started to paint a two-degree warmer world as quite a scary one.

“That combination of science and morality I think brought it here in a way that was just undeniable,” said Jennifer Morgan, director of the climate-change program at the World Resources Institute. “That’s how I think it got as far as it’s gotten.”

But the talk of 1.5 degrees brings with it deeply sobering implications that, until now, many in the climate debate largely managed to avoid or ignore.

Increasing talk about this target also opens up, more than ever, a troubling discussion about “negative emissions” technologies that do not exist on any mass scale at present but theoretically would be able to pull carbon dioxide out of the air. Perhaps the most popular of them is bioenergy with carbon capture and storage, or BECCS, which would involve burning plants for power and then storing the carbon released in the ground.

These technologies will be needed, scientists say, for 1.5 to be possible. It may be that the only way to land the planet at 1.5 degrees is to temporarily overshoot that target and then cool things back down again through massive carbon removal from the air, according to scientists.

Criticisms of “negative emissions” technologies are mounting. Recently, a large group of scientists said it would be “extremely risky” to rely on such technologies rather than simply cutting carbon emissions sharply, because they all have major trade-offs (BECCS, for instance, would require a huge amount of land). But nonetheless, they’ve become a part of the debate out of necessity.

Thus, the powerful moral case made by small island nations and other climate-vulnerable countries now runs head on into the extraordinarily complex math of the global carbon budget, with a little science fiction thrown in to boot.

But even if humans cannot manage to keep the planet from warming more than 1.5 degrees Celsius, there could be a benefit to the effort.

“Having aimed for 1.5 in the first place,” Rogelj said, “if we are not lucky, if some technologies don’t turn out, then maybe we will be safe enough to stay below two degrees.”

More at Energy & Environment:

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