1.5°C = Too Much? Why Scientists Are Now Eyeing a Cooler Target
A new study suggests the Paris Climate Agreement’s target might not protect Earth’s ice sheets — or our coasts
I remember standing on a lake in Alaska, looking out toward a distant glacier as it calved into the sea. The sound was thunderous, like a distant drum roll, followed by eerie silence.
We’d been camping nearby, and at the time, I was studying how changing climates had shaped the land over millennia. But this wasn’t ancient history. This was now. The glacier was retreating fast, and the rocks beneath our feet told stories of a time when it had stretched much farther into the bay.
Back then, we were looking for evidence of past climate shifts, trying to understand how ancient environments responded to warming. But the work always left me wondering: how close are we to crossing similar lines today?
Turns out, maybe closer than we thought.
A new review published in Communications Earth & Environment pulls together decades of evidence, from ancient shorelines to satellite data, and delivers a loud message: even if we limit warming to the Paris Agreement’s “safe” target of 1.5°C above pre-industrial levels, it might not be enough to stop the polar ice sheets from melting into the sea.
In fact, the authors argue that the actual threshold for preventing irreversible damage might be as low as 1.0°C, lower than where we are right now.
“There is a growing body of evidence that 1.5°C is too high for the ice sheets in Greenland and Antarctica,” says Professor Chris Stokes, lead author of the study from Durham University. “Recent observations of ice sheet loss are alarming, even under current climate conditions.”
They’re not being dramatic. Today, the ice sheets in Greenland and Antarctica are losing around 370 billion metric tons of ice each year. That’s quadruple what we saw in the 1990s, and we’re only at around 1.2°C of warming. If this rate continues, or worsens, sea levels could rise by several meters in the coming centuries. For perspective: 230 million people currently live within one meter of sea level.
And no, this isn’t just about future generations. The paper notes that sea levels could start rising by more than one centimeter per year within the lifetime of today’s children. That kind of change would overwhelm most adaptation efforts, especially in low-lying nations.
To support their conclusions, the authors reviewed multiple lines of evidence. They looked at past warm periods when temperatures were similar to or slightly higher than today. These windows into deep time, like the Last Interglacial (about 125,000 years ago) or the Pliocene (around 3 million years ago), help researchers understand how Earth’s climate and ice sheets responded to small temperature increases.
During these periods, sea levels were several meters higher than today, despite carbon dioxide levels being similar to, or even lower than, current concentrations.
They also analyzed recent satellite measurements showing accelerating ice loss and paired that with modeling studies projecting future sea-level rise under different warming scenarios. While some models still offer a range of possible outcomes, a common thread emerged: keeping global temperatures at or above 1.5°C locks us into long-term ice loss.
Worse still, the melting can trigger feedback loops. When ice sheets melt, they lower in elevation, exposing their surface to warmer air. This speeds up melting even more.
Ice sheets that sit below sea level, like parts of West Antarctica, can also become unstable once the ocean gets under them. These runaway processes are incredibly hard to reverse. Even if we brought temperatures back down in a few decades, the damage might be done.
What stood out to me most was the concept of a “safe” climate threshold not being fixed. It’s easy to think of 1.5°C as a line in the sand, but Earth doesn’t operate on rigid rules. The ice doesn’t care what our political agreements say; it responds to physics, not pledges.
This idea that today’s conditions might already be too warm to prevent irreversible sea-level rise is a gut punch, especially for those of us who work in conservation. It’s not just about projections anymore. We can see it happening. We can hear it cracking.
Professor Rob DeConto, one of the co-authors, warns that even if we manage to cool the planet in the future, “it will still take hundreds to perhaps thousands of years for the ice sheets to recover. If too much ice is lost, parts of these ice sheets may not recover until the Earth enters the next ice age.”
In other words, the land we lose to sea-level rise? It’s gone for a very, very long time.
So, where does that leave us?
The researchers call for urgent action, not just to meet the Paris targets, but to revisit them. They argue we need more research to define a truly safe limit for the ice sheets. But based on the data we already have, they propose a lower goal: keeping warming closer to 1.0°C.
That might sound impossible, but the authors say there’s still room for hope. “We only have to go back to the early 1990s to find a time when the ice sheets looked far healthier,” Dr. Stokes points out. Back then, temperatures were roughly 1.0°C above pre-industrial levels, and CO₂ concentrations were about 350 parts per million. Today, we’re at 424 ppm and counting.
To me, this reinforces something I’ve always believed: every fraction of a degree matters. We can’t afford to treat 1.5°C as a comfort zone. It’s more like a last-ditch emergency brake, and even that might not be enough.
The study doesn’t offer a miracle solution, but it does offer clarity. And sometimes, that’s exactly what we need to take the next step.
Published in Fossils et al. Follow to learn more about Paleontology and Evolution.
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Best,
Sílvia P-M, PhD Climate Ages
