UN hopes to hold global temps at 1.5 C. It’s unlikely.

By Chelsea Harvey | 04/24/2024 06:59 AM EDT

Climate Promise 2025 highlights the disconnect between U.N. messaging and the growing possibility of overshooting a key global warming threshold.

United Nations Development Programme Administrator Achim Steiner speaks to reporters during a news conference on March 9, 2023, at U.N. headquarters.

United Nations Development Programme Administrator Achim Steiner speaks to reporters during a 2023 news conference. UNDP's Climate Promise 2025 aims to strengthen pledges from countries to reduce emissions in line with limiting global warming to 1.5 degrees Celsius. Mary Altaffer/AP

NEW YORK — The United Nations Development Programme launched a new program Tuesday that aims to galvanize countries around stronger climate action — and keep global warming below 1.5 degrees Celsius.

Known as Climate Promise 2025, the plan centers on strengthening the carbon-cutting pledges that countries will update next year under the Paris climate agreement. It’s the latest stage of UNDP’s Climate Promise program, which worked with 128 countries on the 2020 round of pledges — known as nationally determined contributions, or NDCs.

“The next two years stand as one of the best chances we have as a global community to course correct our collective path and ensure warming stays below 1.5 degrees Celsius, staving off the worst effects of climate change,” said Achim Steiner, UNDP administrator, at an event launching the initiative in New York on Tuesday.


Yet scientists warn that the 1.5-degree target — the Paris Agreement’s most ambitious goal — is already all but out of reach. Global efforts to reduce greenhouse gas emissions aren’t happening fast enough, and many experts say it’s virtually certain that the world will at least temporarily overshoot that threshold.

It’s the latest example of a growing divide between the public messaging from many world leaders and the warnings from scientists that a breach of the 1.5-degree target is already imminent. The disconnect raises questions about how — and whether — world leaders should communicate the growing possibility of an overshoot.

“Sooner or later, policymakers will have to embrace the ‘overshoot story’ if they want to stick to 1.5C,” said Oliver Geden, a climate policy expert at the German Institute for International and Security Affairs, in an email to POLITICO’s E&E News.

If world leaders accept the likelihood of an overshoot, they can begin to consider ways to reverse it, Geden added. It’s possible for the world to temporarily exceed the 1.5-degree target and later use technological means to bring global temperatures back down — for instance, by drawing carbon dioxide back out of the atmosphere, in a strategy known as “negative emissions.”

Most potential global cooling strategies are still unproven at large scales, making them an uncertain solution. It’s not clear any of the technologies will ever be feasible at all, Geden said.

But “negative emissions” strategies are among the only methods that could keep the 1.5-degree target alive after an overshoot.

That means policymakers “would need to plan for and to communicate that the world needs to reach net-negative CO2 emissions after reaching net-zero around 2050,” Geden said.

But other experts argue that public messaging around the 1.5-degree target shouldn’t change, even if overshoot becomes unavoidable. The world must still continue to rapidly reduce greenhouse gas emissions to keep as close to the original target as possible.

“You need to do the same things whether you’re aiming for 1.5 or for 2 [degrees],” said Laura Pereira, a researcher at the University of the Witwatersrand in South Africa. “It’s just that if you act now and do it rapidly enough, you can do 1.5.”

Some experts also worry that declaring an overshoot inevitable could also potentially hamper the momentum of global climate action plans.

“As soon as you throw your hands up in the air and say, ‘Oh, we’re going to overshoot,’ you’re not going to have those hard discussions about what really needs to change,” Pereira said.

‘Becoming inevitable’

The debate is likely to intensify as the 1.5 degree threshold draws closer.

Global emissions would have to peak by 2025 and then fall a staggering 42 percent by 2030 in order to keep warming below 1.5 degrees, according to the U.N.’s Intergovernmental Panel on Climate Change, the world’s top authority on global warming. The world would then need to hit net-zero emissions around 2050.

“Regarding the reachability of the 1.5ºC target, truly transformative action is needed to still be able to achieve the 1.5ºC goal without an at least temporary overshoot,” said Nico Wunderling, a scientist at the Potsdam Institute for Climate Impact Research in Germany, in an email.

Human societies can only emit a limited amount of additional carbon without overshooting the target, Wunderling added, and research suggests the planet is likely to burn through that budget within the next five years if greenhouse gas emissions don’t swiftly and dramatically drop.

So while it’s not impossible, he said, it’s “extremely ambitious” for the world to reach net-zero emissions in time to avoid 1.5 degrees of warming.

The world could still limit warming to 1.5 degrees after a short period of overshooting the target, he said. But the impacts of climate change worsen with every fraction of a degree the planet warms. And some consequences, like sea-level rise or plant and animal extinctions, can’t be easily reversed once they’ve happened, even if global temperatures later fall.

So if the world does blow through 1.5 degrees, scientists say, it’s crucial to limit the overshoot as much as possible.

That’s a growing concern among climate experts. Scientists have quietly warned for years that the world is unlikely to meet the 1.5-degree target. But their message has grown more urgent in the last few years.

Scientists were candid about the impending risks during their presentation of the third and final installment of the IPCC’s most recent major assessment report in April 2022.

“It is almost inevitable that we will at least temporarily overshoot 1.5,” Jim Skea, an energy expert at Imperial College London and co-chair of the IPCC working group that prepared the report, said at a 2022 virtual presentation of the findings.

Another U.N. report in 2022 warned that countries’ carbon-cutting pledges were too weak and, as of that moment, there was “no credible pathway” to 1.5 C. And the 2023 emissions gap report, released in November, reiterated that failing to sufficiently reduce emissions over the next six years will make it “impossible to limit warming to 1.5C with no or limited overshoot.”

In December, leading international scientists presented an annual report to the U.N. on the year’s top climate insights. It concluded that overshooting the 1.5-degree target is “becoming inevitable.”

Immediate, radical and transformative action could technically still keep the target alive, the report noted. But the diminishing probability means that world leaders must also work to minimize overshoot as much as possible.

“Governments, corporations and other actors must now focus on minimizing the magnitude and duration of overshoot, while still acting to avoid it,” the report warns.

Keeping the target alive

U.N. messaging remains focused on staying below 1.5 degrees — period.

“We believe it is worth trying to bring the world together through nationally determined contributions to a scenario where 1.5 C remains at least within the realm of possibility,” said Steiner, UNDP’s administrator, at Tuesday’s Climate Promise launch.

The new initiative aspires to bring the next round of national pledges in line with the IPCC’s requirements for staying under 1.5 degrees. The plan takes a three-pronged approach, aiming to help countries scale up their ambition, accelerate their progress and increase the inclusivity of their climate plans, acknowledging the disproportionate impacts of global warming on Indigenous communities and other vulnerable populations.

“It’s make or break for the 1.5-degree limit,” said U.N. Secretary-General António Guterres at Tuesday’s launch event. “Today, humanity spews out over 40 gigatons of carbon dioxide every year. At this rate, the planet will soon be pushed past the 1.5-degree limit. Countries’ ambitious new national climate plans — which are due next year — are essential to avert this calamity.”

When the Paris Agreement was first adopted in 2015, scientists estimated that the world was on track for about 3.5 degrees of global warming, said Cassie Flynn, UNDP’s global director of climate change, at Tuesday’s launch. But the world has made progress since then — the current Paris climate pledges are consistent with warming of around 2.5 degrees.

The next round of national contributions could still bring that trajectory down by another degree, she said.

Technically speaking, the world could cut emissions in line with keeping global warming under 1.5 degrees. But that would require a Herculean overhaul of the global economy in record time, an unprecedented feat in human history.

Many scientists say that scenario is unlikely. But the fact that hitting the target is still technically feasible — at least for a few more years — keeps the idea of avoiding overshoot alive for now.

“The goal of staying under 1.5 degrees is alive until overshoot,” Pereira said. “You can always change things fundamentally.”