Even if the world successfully limits global warming to the ambitious 1.5C target, coastlines around the globe remain at serious risk from rising sea levels in the centuries ahead, according to a new warning from leading climate scientists.
Nearly 200 countries have pledged to aim for the 1.5C threshold, but researchers now caution that this milestone should not be considered “safe” for vulnerable coastal populations. Their conclusions, based on the latest research into shifting ice sheets and historical climate data, underscore that sea-level rise will continue regardless – and that even small reductions in warming make a crucial difference.
Current policies place the world on a path to almost 3C of warming by 2100 compared to pre-industrial levels. However, even reaching the 1.5C target will not prevent the ongoing melting of Greenland and Antarctic ice, scientists say, as these massive ice sheets respond to temperature changes over centuries.
“Limiting warming to 1.5C would be a major achievement – it should absolutely be our target – but in no sense will it slow or stop sea-level rise and melting ice sheets,” said Prof Chris Stokes, glaciologist at Durham University and lead author of the new paper published in Communications Earth and Environment.
Previous interpretations of the 2015 Paris climate agreement, which aimed to keep temperature rises “well below” 2C and ideally 1.5C, have sometimes simplified the lower target as a guarantee of safety. Glaciologists, however, have long warned against this assumption.
The researchers used three key lines of evidence to highlight the dangers:
- Records of Earth’s distant past reveal significant melting and sea levels several metres higher than today during previous warm periods, including 125,000 years ago.
- When atmospheric carbon dioxide was last at today’s levels – around 3 million years ago – sea levels stood 10 to 20 metres higher.
- Current observations show melting rates are increasing, especially in west Antarctica and Greenland, although east Antarctica remains more stable for now.
Prof Jonathan Bamber, director of the Bristol Glaciology Centre, added, “We’re starting to see some of those worst-case scenarios play out almost in front of us.”
Computer models simulating the future of ice sheets paint a grim picture. According to Prof Stokes, “Very, very few of the models actually show sea-level rise slowing down if warming stabilises at 1.5C, and they certainly don’t show sea-level rise stopping.”
The greatest concern is that melting could accelerate further past unknown “tipping points” triggered by ongoing warming, though the specifics of these processes are not yet fully understood.
Prof Andy Shepherd, glaciologist at Northumbria University, not involved in the new study, said, “The strength of this study is that they use multiple lines of evidence to show that our climate is in a similar state to when several metres of ice was melted in the past. This would have devastating impacts on coastal communities.”
An estimated 230 million people currently live within one metre of high tide lines. While defining a “safe” warming limit is complicated by the differing vulnerabilities of populations, the researchers warn that a sea-level rise of one centimetre per year or more by century’s end – mostly due to melting ice and warming oceans – could overwhelm even wealthy nations’ ability to cope.
“If you get to that level, then it becomes extremely challenging for any kind of adaptation strategies, and you’re going to see massive land migration on scales that we’ve never witnessed in modern civilisation,” said Prof Bamber.
Despite these alarming predictions, scientists stress that there is still time to make a difference. “The more rapid the warming, you’ll see more ice being lost and a higher rate of sea-level rise much more quickly,” Prof Stokes concluded. “Every fraction of a degree really matters for ice sheets.”
