Workers dismantle the venue that hosted the U.N. conference on climate change in Le Bourget, on the outskirts of Paris, on Monday. (Adrien Morlent/AFP via Getty Images)

In Saturday’s historic Paris agreement to address climate change, 195 countries pledged that they would take steps to limit the planet’s warming to “well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C.”

But we’re already quite close to 1 degrees C now — or, translated for U.S. audiences, a 1.8 degrees Fahrenheit rise over the temperatures of pre-industrial times. Which forces the question: What kinds of emissions cuts will be necessary to hit these targets, given that the current pledges would lead to a world at 2.7 degrees C or even higher?

Two recent analyses show that keeping warming below 2 degrees and keeping it to about 1.5 degrees are still possible — theoretically. However, in each case, doing so would be a gigantic endeavor, requiring not only considerable improvements on current carbon-cutting pledges, but additional steps or technologies in some cases.

On Monday, Climate Interactive, working in collaboration with MIT’s Sloan School of Management, released an  analysis showing how the structure of the Paris agreement — which involves ratcheting up countries’ emission-cutting pledges every five years — could lead to a scenario in which temperatures are held to about 1.8 C. This is a world in which there would still be quite serious threats to ice sheets, permafrost and much more — but also far from the worst-case scenario.

To get there, though, all of the big players — the United States, the European Union, China and others — would have to step up their carbon-cutting games, in some cases quite dramatically. The United States, for instance, would have to progress from its pledge of reducing emissions 26 percent to 28 percent below 2005 levels by 2025, to a pledge to cut them 45 percent below that level by 2030. That’s a big step up in ambition — and the ambition could only increase after 2030.

Similarly, China would have to peak its emissions in 2025, not 2030, and India, whose emissions are set to grow greatly, would have to agree to peak them by 2027.

It’s not at all clear that we will get this much climate progress this fast. But assuming that we do, warming might stabilize at 1.8 degrees C above pre-industrial levels — but, notably, with a huge uncertainty range of 0.9 to 2.4°C. In other words, we could quite easily go through all this effort and then overshoot the goal anyway.

Here’s a telling figure provided by Climate Interactive, showing how current pledges by countries (“INDCs”) take the world off the worst-case path for warming, but also how far they are from the “safe” path of less than 2 degrees C:


Climate Interactive/MIT Sloan

But of course, the Paris agreement also mentions that the world should strive for an even stronger climate goal, of limiting warming to 1.5 degrees C, which would undoubtedly be safer (but would also risk some serious impacts). So is that possible, too?

Myles Allen, a climate scientist at the University of Oxford who specializes in carbon budgets, just released an analysis showing that it is….but, well, it kind of depends on what you mean by possible. “Possible does not mean straightforward,” he writes.

Allen’s analysis shows that to have a chance at 1.5 degrees C, you need really sharp cuts in carbon dioxide emissions, as well as major cuts to short-lived climate pollutants (methane, soot), and, finally, carbon dioxide removal from the atmosphere (using technologies that don’t exist yet on a large scale).

And still, it’s only a chance, not a guarantee. For the analysis also assumes that “the climate system response turns out to be in the lower half of the current range of uncertainty,” Allen writes.

These are not the only analyses or the only scenarios. There are multiple groups out there counting carbon, running models and trying to figure out whether we can really, safely, land this plane.

But the analyses, although they vary, tend to have some themes in common. One of them is that the quest to limit warming to a particularly low amount, to hit a particular stringent target, will require not only emissions cuts but also the development of key new technologies. The second is that all of this remains clouded, to a major extent, by scientific uncertainty.

In other words, whenever we pick a temperature goal, and compute how much carbon we can release and still stay below it — and how much countries’ policies must, therefore, strengthen — there’s still always a substantial chance that we could be wrong.

What’s so important about Paris, then, is that countries of the world have finally committed to at least addressing those parts of this equation that they can actually control.

More at Energy & Environment:

Holding warming under two degrees Celsius is the goal. But is it really attainable?

This huge deal is the latest evidence that the battery revolution has arrived

Another danger of climate change: Giant flying boulders?

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