Since then, scientists have increasingly affirmed that, yes, this is the right target to be shooting for. Stopping warming somewhere between 1.5 and 2 degrees Celsius, according to a recent analysis, would still pose a severe threat to coral reefs and the stability of West Antarctica but might avoid most other grave tipping points in the climate system, such as the collapse of East Antarctic glaciers or wintertime Arctic sea ice.

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With a little luck, then, such a target could indeed avoid the worst of what has been conjured in a world of runaway climate change. However, there’s a big problem: hitting the target.

Both before and after the Paris climate agreement, analyses by authorities including the International Energy Agency and the United Nations Framework Convention on Climate Change found that countries’ promises to cut their emissions just weren’t ambitious enough to keep the world within the “safe” climate range that lies at the core of the Paris agreement. Such analyses suggested, again and again, that without more ambitious action on the part of individual countries, global greenhouse gas emissions would still rise in the future, and warming might peak at temperatures well above 2 degrees Celsius.

Now, in a study in Nature, a large team of researchers reaffirm this troubling conclusion in a sweeping manner, by not only reexamining the individual country pledges — also known as Intended Nationally Determined Contributions, or INDCs — but also conducting a meta-analysis of all the past analyses that have already determined that the Paris pledges fall short.

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And they, too, find after taking stock of all of this research that the current pledges are likely to leave temperatures at 2.6 to 3.1 degrees Celsius warmer than pre-industrial levels by the year 2100, assuming that the pledges themselves are adopted and only their unconditional parts are realized. Indeed, under the pledges, the full carbon “budget” that we have left to emit if we want a good chance of staying below 2 degrees Celsius of warming could be emitted by 2030, the research finds.

The 2.6 to 3.1 degrees Celsius number sounds bad enough, but, in fact, it is merely the range that we would have 50 percent probability of not exceeding under the current pledges. But if you ask a different question — what level of warming can we avoid with a 90 percent probability? — then it looks worse.

“The current INDCs still imply an almost 10 percent risk of temperatures still hitting 4 degrees,” says Joeri Rogelj, a researcher with the International Institute for Applied Systems Analysis in Austria who is the lead author of the research. He collaborated with a group of nine researchers from Switzerland, the Netherlands, Germany, the U.S., South Africa, Brazil, China and Australia.

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The new analysis also all but rules out the possibility of keeping warming firmly below 1.5 degrees Celsius, a target hoped for by many small island and climate-vulnerable nations.

“The window for limiting warming to below 1.5 °C with high probability and without temporarily exceeding that level already seems to have closed,” the study notes — although if we someday adopt “negative emissions” technologies, such as direct air capture of carbon dioxide, then we might at least be able to exceed 1.5 degrees Celsius but then cool the planet down below it again.

There is basically only one way of interpreting this analysis: The world needs increased ambition, and it needs it fast. After all, every year without such elevated ambition means more emissions and thus a larger cumulative burden of the long-lived greenhouse gas, carbon dioxide, in the atmosphere. And with every year of emissions, the allowable carbon “budget” to keep global warming below 2 degrees Celsius shrinks further.

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“The agreement by itself might be sufficient, but the coming five to 10 years will show how the decisions will be implemented, and then we will know whether it is actually effective or not,” Rogelj says. “Not everything was decided in Paris, and some of these things still need to be carved out over the coming five to 10 years.”

The first order of business, then, is getting the Paris agreement into force — it needs 55 countries, representing 55 percent of total emissions, to sign and join for that to happen. So far, only 18 countries have gone this far – and they only represent 0.18 percent of emissions. However, bigger emitters such as the U.S. and China are expected to fully sign on soon.

After that, Rogelj notes that there will be a global “stock-take” under the agreement in 2018. And that would be a pretty good time for nations of the world to look at an analysis like his and begin a course correction. Perhaps, at that time, the future of clean energy will look even brighter than it does today (it already looks pretty bright).

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And there’s another catch: If countries do not act fast to increase their carbon-cutting, then with every passing year, they will necessarily grow more committed to a future in which only so-called “negative emissions” technologies, which would withdraw carbon dioxide from the air, can keep the planet’s warming within the Paris goals.

“The literature has shown that earlier action strongly reduces your dependencies on these negative emissions, because you don’t exceed the allowed budget in the first place; you don’t need to bet on them actually removing CO2 from the atmosphere to get back within your maximum budget,” Rogelj says.

Still, it seems likely that some deployment of these technologies — such as carbon capture and storage, combined with the burning of biomass for energy — will be needed.

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In the end, then, the Paris agreement looks like a great breakthrough — and yet only the beginning. Whether its stunning and ambitious goals can be realized lies very much in our hands. Achieving them, meanwhile, suggests a world with far greater unity, and foresight, than we’re seeing at the moment.

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