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Even if the world succeeds in limiting global warming to 1.5°C, the planet could still face sea-level rise of several metres over the coming centuries, scientists have warned in a new study.
Although nearly 200 countries have pledged to try and keep temperature rise below 1.5°C under the 2015 Paris Agreement, the new research stresses that this should not be seen as a “safe” target, especially for people living near coasts.
The study, published in the journal Communications Earth and Environment, pulls together the latest evidence from observations, historical records, and computer modelling of ice sheets to understand future risks.
Limiting warming helps but won’t stop sea rise
“Our key message is that limiting warming to 1.5°C would be a major achievement, which should absolutely be our target, but in no sense will it stop sea-level rise and melting ice sheets,” said lead author Professor Chris Stokes, a glaciologist at Durham University.
Greenland and Antarctica will continue to melt even if warming stops at 1.5°C, the study shows, because these giant ice sheets respond slowly over centuries to temperature changes.
What the past tells us
The researchers pointed to past warm periods in Earth’s history as strong warnings. Around 1,25,000 years ago, when global temperatures were similar to today, sea levels were already several metres higher.
Going back even further, around 3 million years ago, carbon dioxide levels were similar to today and sea levels were estimated to be 10-20 metres higher than current levels.
Current signs of trouble
Today, there are already signs of accelerating ice melt. “Pretty dramatic things [are] happening in both West Antarctica and Greenland,” said Professor Jonathan Bamber, co-author and director of the Bristol Glaciology Centre.
East Antarctica appears more stable for now, but some early signs of ice loss have also been noticed.
Future models give bleak predictions
Computer models simulating how ice sheets will respond to future warming show worrying results. “Very, very few of the models actually show sea-level rise slowing down if warming stabilises at 1.5°C, and they certainly don’t show it stopping,” said Prof Stokes.
The researchers say that beyond a certain level of warming, we may cross “tipping points” that trigger unstoppable ice loss. However, the exact thresholds remain uncertain.
Professor Andy Shepherd from Northumbria University, who was not part of the study, said the strength of the research lies in its use of “multiple lines of evidence” showing that today’s climate is similar to past periods when major ice loss occurred, reports BBC.
“This would have devastating impacts on coastal communities,” he said.
A threat to millions
An estimated 230 million people live within one metre of current high tide levels, putting them at high risk from rising seas.
If sea-level rise reaches one centimetre per year by the end of this century, adaptation could become extremely difficult, even for wealthy countries.
“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),” warned Prof Bamber.
Urgent action still matters
Despite the grim outlook, the scientists stress that every fraction of a degree we can avoid still matters. A slower rate of warming would allow more time to prepare, adapt, and protect vulnerable populations.
“The more rapid the warming, you’ll see more ice being lost and a higher rate of sea-level rise much more quickly,” said Prof Stokes.
“Every fraction of a degree really matters for ice sheets.”
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