Even if global heating stays at today's level, the world could be headed for unstoppable sea level rise and mass migration, scientists have warned in a stark new report in the journal Communications Earth and Environment.

Ice loss especially from Greenland and Antarctica has rocketed since the 1990s, now making up the lion’s share of sea level rise. This upward trend, driven by climate change, is speeding up faster than countries can adapt, notes the Guardian.

The 1.5C global warming limit – once seen as a critical line and the basis of the Paris Agreement – will not be enough to prevent dramatic shifts in coastlines. Even if emissions are slashed overnight, oceans could still rise 1cm a year by 2100, outpacing efforts to build defences, said the scientists.

And the world isn’t on track for 1.5C. Projections point to a much hotter future – around 2.5C to 2.9C – raising the risk of crossing irreversible tipping points, including the collapse of major ice sheets, said the Guardian.

If that happens, sea levels could surge by up to 12 metres. That would redraw maps and displace millions.

Over 230mn people currently less than one metre above sea level. With just a 20cm rise by mid-century, annual flood damage could top $1 trillion in the world’s largest coastal cities.

Every decimal of warming avoided can slow this down, the researchers stress. It buys time, eases human suffering and keeps some adaptation within reach.

The new study draws from ancient climate records, satellite observations and cutting-edge modelling. It paints a clear picture: sea level rise is no longer a distant threat.

In fact, a one to two metre rise is now seen as inevitable. In the UK, that could submerge vast areas like the Fens and Humberside. Globally, developing countries with fewer resources – such as Bangladesh – face the gravest danger.

One metre of rise could sink parts of Belize’s largest city. "That’s not a distant future – that’s within reach," Carlos Fuller, the country’s long-time climate envoy, told the newspaper.

According to Professor Jonathan Bamber of the University of Bristol in England, the situation becomes nearly impossible to manage when seas rise faster than 1 cm a year. "Adaptation at that speed? Very unlikely. Migration would be unavoidable," he told the Guardian.

“What we mean by safe limit is one which allows some level of adaptation, rather than catastrophic inland migration and forced migration, and the safe limit is roughly 1 cm a year of sea level rise,” he added.

The last time Earth had this much CO₂ in the air, seas were 10 to 20 metres higher. Ice loss then took centuries to unfold – but the same mechanisms could now be kicked into gear with just a few more tenths of a degree. Even if temperatures fall in future centuries, ice sheets take millennia to bounce back.