Paris Climate Goal of 1.5°C Still Too Warm to Save Polar Ice Sheets

The celebrated 1.5°C temperature target of the Paris Climate Agreement may not be strict enough to prevent catastrophic melting of Earth’s polar ice sheets, according to new research. Scientists examining multiple lines of evidence suggest we need to aim even lower – closer to 1°C above pre-industrial levels – to avoid several meters of unstoppable sea level rise over coming centuries.

The study, published in Communications Earth & Environment, combines recent satellite observations, climate modeling, and evidence from Earth’s past to reveal that current warming of approximately 1.2°C is already pushing ice sheets in Greenland and Antarctica dangerously out of balance. Their continued melting poses an existential threat to coastal communities worldwide, potentially displacing hundreds of millions of people.

But just how low would global temperatures need to go to keep our ice sheets intact and coastlines stable? This question has gained new urgency as scientists observe alarming rates of ice loss occurring much sooner than predicted.

Ice Loss Accelerating Beyond Predictions

Earth’s ice sheets in Greenland and Antarctica together store enough water to raise global sea levels by nearly 65 meters if they were to melt completely. While complete melting would take many centuries, the current rate of loss is already concerning.

“The mass of ice lost from these ice sheets has quadrupled since the 1990s and they are currently losing around 370 billion tonnes of ice per year, with current warming levels of around 1.2°C above pre-industrial temperatures,” the researchers note.

What makes these findings particularly troubling is that satellite measurements show ice loss accelerating beyond what climate models had predicted, suggesting the ice sheets are more sensitive to warming than previously thought.

“Recent satellite-based observations of ice sheet mass loss have been a huge wake-up call for the whole scientific and policy community working on sea level rise and its impacts,” said Jonathan Bamber, Professor of Glaciology and Earth Observation at the University of Bristol and co-author of the study. “The models have just not shown the kind of responses that we have witnessed in the observations over the last three decades.”

Key Findings from the Research

• Ice sheet mass loss has quadrupled since the 1990s, now totaling approximately 370 billion tonnes per year
• Current warming of 1.2°C is already generating substantial ice loss in both Greenland and Antarctica
• Evidence from past warm periods indicates that 1.5°C warming would likely generate several meters of sea level rise
• Ice sheet “tipping points” may have already been passed in the most vulnerable regions
• Once lost, ice sheet recovery would take hundreds to thousands of years
• Researchers suggest a safer temperature target closer to 1°C above pre-industrial levels

Lessons from Earth’s Past

The research team examined evidence from previous warm periods in Earth’s history that were similar to or slightly warmer than present day. This evidence consistently shows that slightly higher temperatures led to significantly higher sea levels.

“Evidence recovered from past warm periods suggests that several meters of sea level rise – or more – can be expected when global mean temperature reaches 1.5°C or higher,” explained Andrea Dutton, Professor at the University of Wisconsin-Madison and study co-author. “Furthermore, this evidence also suggests that the longer those warm temperatures are sustained, the greater the impact on ice melt and resulting sea-level rise.”

The team’s findings align with a growing body of research suggesting that the 1.5°C target, while better than higher warming scenarios, still represents a dangerous threshold for Earth’s ice sheets.

Permanent Changes on Human Timescales

A critical aspect of ice sheet loss is its effective permanence on human timescales. Unlike some other climate impacts that might reverse relatively quickly if temperatures decrease, ice sheets would take centuries or even millennia to regrow.

“It is important to stress that these accelerating changes in the ice sheets and their contributions to sea level should be considered permanent on multi-generational timescales,” said Rob DeConto, Professor from the University of Massachusetts Amherst and study co-author.

“Even if the Earth returns to its preindustrial temperature, 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, land lost to sea level rise from melting ice sheets will be lost for a very, very long time. That’s why it is so critical to limit warming in the first place.”

Real-World Implications

The research has profound implications for coastal cities, island nations, and hundreds of millions of people living in low-lying areas. Currently, about 230 million people live within one meter of sea level, and around one billion inhabit land less than 10 meters above sea level.

Ambassador Carlos Fuller, long-time climate negotiator for Belize, emphasized the real-world implications: “Findings such as these only sharpen the need to remain within the 1.5°C Paris Agreement limit, or as close as possible, so we can return to lower temperatures and protect our coastal cities.”

Fuller noted that Belize long ago moved its capital inland, but its largest city will be inundated by just one meter of sea level rise.

Aiming for a Safer Target

Lead author Chris Stokes, Professor in the Department of Geography at Durham University, stressed that while limiting warming to 1.5°C would be a significant achievement, we should be aware it may not prevent rapid sea level rise.

“There is a growing body of evidence that 1.5°C is too high for the ice sheets in Greenland and Antarctica. We’ve known for a long time that some sea level rise is inevitable over the next few decades to centuries, but recent observations of ice sheet loss are alarming, even under current climate conditions,” said Stokes.

“Limiting warming to 1.5°C would be a major achievement and this should absolutely be our focus. However, even if this target is met or only temporarily exceeded, people need to be aware that sea level rise is likely to accelerate to rates that are very difficult to adapt to – rates of one centimetre per year are not out of the question within the lifetime of our young people.”

The researchers suggest that a safer global temperature target would be closer to 1°C above pre-industrial levels – similar to conditions in the early 1990s when ice sheets appeared much healthier. Back then, carbon dioxide concentrations were around at 350 parts per million, compared to approximately 424 parts per million today.

“We are not necessarily saying that all is lost at 1.5°C,” Stokes added, “but we are saying that every fraction of a degree really matters for the ice sheets – and the sooner we can halt the warming the better, because this makes it far easier to return to safer levels further down the line.”