LE BOURGET, France — The U.N. Climate Summit in Paris, also known as COP21, appears poised to deliver a new global climate agreement that has a goal of limiting global warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above preindustrial levels, or possibly language calling for keeping warming to "below 2 degrees Celsius."

This is more ambitious than the 2 degrees Celsius, or 3.6 degrees Fahrenheit, target countries were previously aiming for.

It's also politically, though not necessarily technically, impossible to achieve, at least in the short run. It's highly likely that the world would blow right past the 1.5-degree target due to emissions-to-date and likely future emissions. It's possible, though, that after that threshold is exceeded, temperatures could gradually be brought back down, though that too is not yet clear.

To get a sense of how close we already are to 1.5 degrees of warming, consider that already, 2015 will mark the first year in which global temperatures will have warmed by 1-degree Celsius above preindustrial temperatures.

To meet such a target, the global community would have to immediately begin to phase out the use of all fossil fuels, getting to near zero emissions by the year 2030, with negative emissions — meaning that more planet-warming carbon is absorbed by forests and trees than is emitted by burning fossil fuels — to follow within a few short decades after that.

That is far more ambitious than any country currently has planned, including the Obama administration, which is seeking to cut emissions to as much as 28% below 2005 levels by 2025, mainly through EPA regulations. And the world's leading emitter, China, has pledged to peak its emissions — not cut them in absolute terms — by the year 2030.

In fact, the emissions pledges that will be enshrined in any Paris agreement that emerges from these talks actually allow for a net increase in emissions through the year 2030, with no planned reductions spelled out beyond that.

Because 1.5C is "possible" if emissions are rapidly zeroed, it's a question about turnover of energy infrastructure. https://t.co/NXsD9sTHlO — David Lea (@DavidWLea) December 10, 2015

According to #UNEP data: shift from 2°C to 1.5°C increases the #EmissionGap by 89% from 9Gt to 17Gt #COP21 pic.twitter.com/00VqUoabRS — Felix Schenuit (@fschenuit) December 10, 2015

The drumbeat for a 1.5-degree target began with small island nations like the Marshall Islands and Tuvalu. These countries say they will sink under rising seas if warming proceeds above that threshold, and warn of the consequences of 2 degrees of warming.

Barbados Environment Minister Denis Lowe said a target of 2 degrees Celsius, which as of Thursday morning was still an option in the draft text, is "not acceptable."

"We won’t sign off on any agreement that represents a certain extinction of our people,” he said, referring to the threat sea level rise poses to low-lying island countries.

While island nations were expected to push for a 1.5-degree target, one of the biggest surprises of the talks so far has been the traction that this target has picked up from countries that are in a very different position than low-lying, small island nations.

The U.S., Canada, Germany and other industrialized nations have backed a goal of holding global warming below 2 degrees Celsius.

U.S. Secretary of State John Kerry (R) walks with White House senior advisor Brian Deese (L) and US Special Envoy for Climate Change Todd Stern (C) to attend a meeting with French Foreign Minister during the COP 21 United Nations conference on climate change at Le Bourget, on the outskirts of Paris, on December 10, 2015. Image: Mandel Ngan/AFP/Getty Images

Glen Peters, a senior researcher at Norway's Center for International Climate and Environmental Research (CICERO), said that using figures from the U.N. Intergovernmental Panel on Climate Change in Oslo, if emissions remain roughly at present-day levels, the remaining quota of emissions that would propel the climate past the 1.5-degree threshold would be burned by 2020.

Peters told Mashable that nations' reduction pledges, known as Intended Nationally Determined Contributions, or INDCs, around 1% per year growth in emissions would take place through 2030.

Based on the INDCs, the world is in for around 3 degrees Celsius, or 5.4 degrees Fahrenheit, of warming through 2100.

The 1.5C window (66%) At current CO2 rates, enough emitted by 2020 With LUC uncertainty, already too late #COP21 pic.twitter.com/DCYcmj4haN — Glen Peters (@Peters_Glen) December 9, 2015

He said you would need a "monumental transformation" of the global economy to happen quickly in order for the more ambitious target to be reached.

To stabilize the climate at a certain amount of warming, Peters said, “you have to have zero emissions, it’s the cumulative emissions that matter," not the emissions of a single year or two, since molecules of carbon dioxide can remain in the air for up to a thousand years.

Recent data from a group of researchers including Peters found that emissions growth slowed or reversed slightly in 2014, but it did not show that the world has definitively turned the corner on solving global warming.

“Emissions must go to zero or close to it,” Peters said. “Hopefully we’re in a period of lower growth… but still we’re expecting the [emissions] growth to continue.”

If the target can't be reached, then what's the point?

Enshrining what is effectively an impossible goal in international law might seem like a rather pointless exercise. However, the high ambition in such an agreement could send a powerful signal to the world's markets that countries intend to move away from fossil fuels and toward clean energy, thereby boosting the clean tech sector.

In addition, the gap between the rhetoric of this agreement, assuming that an agreement is reached in the end, and the commitments contained within it could be a boon to climate activists.

"We have a 1.5-degree target in a 3-degree agreement,” Bill McKibben, co-founder of 350.org, told Mashable in an interview.

He said the conflict between the draft agreement's aspirations and it's actual provisions is “like announcing that you’re giving up smoking, except that you’re also stopping by the Costco on the way home to get 70 cartons. "

"There’s no squaring it," he said. "I mean, it’s a good thing to have the ambition, but if you have an ambition without a plan to get there... There’s something mildly juvenile about that.”

He said 350.org and other groups will use the goal to put pressure on governments and companies to scale up their levels of ambition too.

“It’s very useful in that we will, trust me, use it as a bludgeon and a lever from this point forward," McKibben said. "They will be reminded often of their rhetorical commitment to a 1.5-degree world.”