What the IPCC really says about 1.5 C

By Chelsea Harvey | 03/21/2023 06:44 AM EDT

The landmark U.N. report was tailored to prepare the world to miss one of its most important climate targets.

Margaret Owen holds a thermometer at Badwater Basin on July 11, 2021, in Death Valley National Park, Calif.

Margaret Owen holds a thermometer at Badwater Basin on July 11, 2021, in Death Valley National Park, Calif. Climate models almost unanimously predict that heat waves will become more intense and frequent as the planet continues to warm. David Becker/Getty Images

The likely failure of the world’s most ambitious climate goal just went mainstream.

Scientists have urged the world for nearly a decade to cap global warming at 1.5 degrees Celsius, beyond which the planet is expected to face increasingly catastrophic climate impacts. Now, they’re warning — in the starkest tones yet — that the world is all but certain to overshoot that threshold.

That’s the message of a dire new report released on Monday by the U.N. Intergovernmental Panel on Climate Change.


“The finding is that almost irrespective of our emissions choices in the near term, we will probably reach 1.5 degrees in the first half of the next decade,” said Peter Thorne, a climate scientist at Maynooth University in Ireland and an author of the report.

Previous U.N. reports have stressed the difficulties of achieving the 1.5 C goal, which requires swift and dramatic emissions reductions in nearly every aspect of society. But it’s only recently that IPCC scientists have begun to publicly acknowledge the near-certainty that the world will miss that target, at least temporarily.

Now that overshoot appears all but inevitable, scientists used the IPCC report to reframe global perceptions about climate successes and failures. Rather than abandoning climate action due to missed goals, they’re stressing that every fraction of prevented global warming — even above 1.5 degrees — still makes a difference. Rapid climate action is more important now than ever, they said.

The ways the world changes in the coming years “will be shaped by the choices we make starting right now,” said IPCC Chair Hoesung Lee. “So let’s hope we make the right choices, because the ones we make now and in the next few years will reverberate around the world for hundreds, even thousands, of years.”

The new report is the final installment in a yearslong climate assessment the IPCC has been conducting since 2015, the same year the Paris climate agreement was adopted. It synthesizes the findings of six previous reports, all summarizing the latest scientific knowledge on the ways the Earth’s climate is changing and how people can halt global warming.

The final report’s overarching conclusion is that climate change is dramatically reshaping the planet, and the world isn’t reducing greenhouse gas emissions fast enough to stop it.

If the 1.5 C target is surpassed, it’s possible that global temperatures could be brought back down by using natural and technological strategies to suck carbon dioxide out of the atmosphere, a technique known as carbon dioxide removal. But that isn’t guaranteed. And the higher global temperatures rise above 1.5 C, the more difficult it will be to bring them back below that threshold.

The report’s conclusions demonstrate how quickly the world has burned through its carbon budget since the Paris accord went into effect less than a decade ago. And it highlights the ways experts have shifted their messaging and their level of optimism around the 1.5 C target in just a few short years.

The 1.5 C target had been a topic of discussion before the Paris Agreement made it a centerpiece of the international climate treaty. It wasn’t originally intended to be the agreement’s primary target. The foremost goal was supposed to be stopping global warming before it surpasses 2 degrees, with 1.5 C being a more ambitious secondary target.

But as scientific evidence grew on the dangers of warming, the 1.5 C target became the primary focus of climate activists and scientists worldwide.

The focus on the 1.5 C target prompted the U.N. Framework Convention on Climate Change — the international body that adopted the Paris Agreement — to commission a special report from the IPCC in 2016. Published two years later in 2018, the report assessed the impacts of global warming likely to occur beyond the 1.5 C threshold. And it estimated the amount of carbon the world had left to burn before blowing past that temperature threshold.

The 2018 report stated that global emissions would need to spiral down to net zero by 2050 in order to keep that target alive, with significant reductions by 2030.

The special report didn’t mince words about the difficulties of achieving the 1.5 C goal. It warned that there was “no documented historic precedent” for the scale of the changes human societies needed to make to avoid that threshold.

But it also didn’t frame the goal as a remote success. Pathways existed to prevent temperatures from reaching 1.5 C — but they required dramatic and immediate reductions in greenhouse gas emissions. It would be difficult, but they were technically possible.

The 2018 report was a blockbuster. It helped spur a new climate movement to reach net zero by 2050. In the years since its release, dozens of nations around the world have set net-zero targets, the United States among them. Many corporations have followed suit.

But it wasn’t enough.

Most net-zero targets are just pledges — they’re not binding and often are not supported by the climate policies that are needed to actually achieve them.

Still, even in 2018, some climate experts were expressing skepticism about the world’s political will to achieve the 1.5 C target. Experts have become more vocal with those concerns in recent years, with many experts now convinced that the target is out of reach (Climatewire, Nov. 11, 2022).

Meanwhile, the world has continued to emit around 50 billion metric tons of carbon dioxide each year since the 1.5 C report was published. That’s despite the report’s call for immediate and drastic emissions reductions.

On the pathway to 1.5 degrees, a few short years make a major difference. Many modeled pathways consistent with achieving the target say emissions should be falling already.

Faced with that reality, the last few IPCC installments have taken a more dire tone than previous reports.

Between August 2021 and April 2022, the organization published a trio of reports summarizing the latest scientific knowledge on the ways the Earth’s climate is changing, the effects on natural systems and what human societies must do to halt the warming. The last of these reiterated that achieving the 1.5 C target would require global emissions to fall by about half in less than a decade and must hit net zero by 2050.

Meanwhile, human societies must radically transform themselves, overhauling just about every aspect of life on Earth.

Still, report authors were frank about the odds of achieving such a dramatic transformation. In April 2022, IPCC report author Jim Skea remarked that “it is almost inevitable that we will at least temporarily overshoot 1.5.” It was some of the starkest language yet around the 1.5 C target.

Monday’s report, which summarizes the findings of all the previous installments since 2015, drives that message home.

The way things are currently going, the 1.5 C target is likely to blow past in about a decade, the report warns. It’s also likely that the world will overshoot the target, at least temporarily, even if people begin to swiftly reduce greenhouse gas emissions.

The possibility of using carbon dioxide removal to cool the Earth’s climate in the future means that overshoot doesn’t necessarily have to be permanent, although the report warns that some climate impacts are irreversible even if global temperatures do eventually fall.

It also clearly states that climate impacts grow worse with every incremental bit of additional warming. It sounds dire, but there’s a bit of hope in that message. It means that every additional bit of warming prevented — even above 1.5 degrees — helps limit the impact of future climate change.

“The real question is whether our will to reduce emissions quickly means we reach 1.5 degrees, maybe go a little bit over and come back down — or whether we go blasting through 1.5 degrees, go through even 2 degrees and keep on going,” said Thorne, the IPCC author. “So the future really is in our hands. We will, in all probability, reach around 1.5 degrees early next decade. But after that, it really is our choice.”