Environmental (Commonwealth Union)_ The world’s coastlines may soon be overwhelmed—not by storms, but by the slow, relentless rise of the sea. A new study warns that even if global warming is limited to the Paris Agreement’s 1.5°C target, sea level rise will become unmanageable, triggering a chain reaction of forced inland migration and long-term devastation.
The study, published in Communications Earth and Environment, warns that the current level of warming (1.2°C) is already enough to accelerate ice loss from Greenland and Antarctica at alarming rates—quadruple what they were in the 1990s. These two massive ice sheets are now the primary drivers of sea level rise, and scientists say we are dangerously close to tipping points that could lead to a dramatic 12-meter rise over time.
“We’re starting to see some of the worst-case scenarios play out almost in front of us,” said Prof. Chris Stokes of Durham University, the study’s lead author. “At the current pace, sea level rise could soon become nearly unmanageable within the lifetime of our young people.”
Even under the most optimistic scenario of rapid cuts in fossil fuel emissions, the study estimates that seas would rise by 1 cm per year by 2100, a rate that would outpace the ability of most nations to build coastal defenses. With the world on track for 2.5°C to 2.9°C of warming, the risks are far more dire.
At those levels of heating, the collapse of the Greenland and West Antarctic ice sheets becomes almost certain. Scientists warn this could lead to the eventual inundation of major population centers worldwide. Currently, over 230 million people live within 1 meter of sea level, and 1 billion reside within 10 meters, many in developing nations with limited capacity for adaptation.
“If sea levels begin rising at a centimetre per year, adaptation becomes nearly impossible,” explained Prof. Jonathan Bamber of the University of Bristol. “That’s when you see catastrophic inland migration, the likes of which modern civilization has never witnessed.”
The economic cost is staggering. Just a 20 cm rise by 2050 could generate $1 trillion in annual flood damages across the world’s 136 largest coastal cities, putting millions of lives and livelihoods at risk.
But perhaps the most disturbing message is this: even 1.5°C of warming doesn’t spare us from disaster. What was once considered a “safe” threshold is now understood to be insufficient for preventing long-term sea level rise. Researchers now believe that a true “safe limit” for Earth’s ice sheets may be closer to 1°C or lower.
The study combined data from past warm periods dating back 3 million years, modern satellite observations, and advanced climate modeling. It revealed that in past eras, just minor increases in temperature triggered self-reinforcing feedback loops that rapidly accelerated sea level rise. After the last Ice Age, for example, seas rose 10 times faster than they do today, driven by relatively modest warming.
“Several metres of sea level rise or more are likely once global temperatures reach or exceed 1.5°C,” said Prof. Andrea Dutton of the University of Wisconsin-Madison, a co-author of the study.
Even if humanity somehow removes excess carbon dioxide and returns the planet to preindustrial temperatures, the damage to the ice sheets may take hundreds or thousands of years to reverse. As a result, land lost to the ocean may remain submerged for millennia, possibly until the onset of a new Ice Age.
Real-world examples offer stark warnings. In 1970, Belize moved its capital inland after a hurricane devastated its coastal hub. Yet today, its largest city remains on the coast, vulnerable to just 1 meter of sea level rise. Carlos Fuller, Belize’s veteran climate negotiator, emphasized:
“These findings sharpen the urgency of staying within the 1.5°C limit or as close as possible to protect our cities and coastal communities.”
With average global temperatures reaching 1.5°C for the first time in 2024, the clock is ticking. Although the Paris Agreement target is measured as a 20-year average, the symbolic crossing of this milestone marks a turning point and a warning.
Sea level rise is the most profound and irreversible long-term consequence of climate change. Human timescales cannot reverse sea level rise, unlike storms or droughts. The world now confronts a crucial decision: either take decisive action or witness the erosion of centuries of civilization.
