The water will keep rising, for centuries after the calendar turns.
Pull up the FireTree flood map, drag the sea level slider to sixty metres, and watch what happens to Cornwall. The familiar boot-shaped peninsula begins to dissolve. Two chunks of it detach entirely from the mainland — the stretch of land running between Carbis Bay and Sennen and St Levan, out near Land's End, becomes a separate island, and so does the arc between Mullion and St Keverne on the Lizard Peninsula. It is a striking image, and it is worth sitting with before asking how seriously to take it.
The sixty-metre figure comes from geologist Edmond Mathez of the American Museum of Natural History, who has estimated that if every scrap of ice on the planet — the Antarctic and Greenland ice sheets, plus mountain glaciers worldwide — were to melt completely, global sea levels would climb roughly seventy metres, submerging every coastal city on earth. That is a geological timescale scenario, not a forecast for the coming decades. But it is the kind of number that makes a flood map genuinely arresting.
The more immediate question is what the next century actually looks like. NASA's assessment is that sea level rise is accelerating — not climbing at a steady, predictable rate, as scientists once assumed, but speeding up incrementally. If that acceleration continues at its current pace, the agency projects a rise of around sixty-five centimetres by 2100. That is enough, NASA notes, to create serious problems for coastal cities. Serious, but not civilisation-ending.
The Royal Society pushes the estimate a little higher. Under a scenario where carbon dioxide and other greenhouse gases keep rising on their current trajectories, it projects somewhere between half a metre and a full metre of additional sea level rise by the end of this century. And crucially, the Royal Society is clear that 2100 is not a finish line. The ocean will keep absorbing heat. Glaciers will keep retreating. The water will keep rising, for centuries after the calendar turns.
The Environment Agency, for its part, is careful about how far it will reach. Asked about extreme scenarios, the agency said that even under its highest-end projections — the kind used for planning purposes around critical infrastructure like nuclear power stations — the sea around Britain could rise by as much as 2.2 metres by the end of 2115. That is a significant number for coastal engineers and planners. But the agency was equally clear that it does not expect Cornwall's geography to change within that window, and it declined to speculate beyond its current modelling.
There is a real tension in how to hold all of this at once. The sixty-metre island scenario is not a lie — it is what the physics eventually produces if you melt everything. But it belongs to a timeframe measured in centuries or millennia, not in the lifetimes of anyone reading about it today. The more pressing reality is the one the Environment Agency and NASA are describing: a world where coastal flooding becomes more frequent and more damaging well within living memory, where the margin for error in coastal planning shrinks, and where decisions made now about emissions and infrastructure will shape what the shoreline looks like for generations.
Cornwall is already one of the parts of England most exposed to that near-term risk. Its long, irregular coastline, its low-lying estuaries, its fishing villages tucked into coves — all of it sits closer to the water than most of the country. The dramatic island maps are a useful way of making the physics visible. But the quieter, less cinematic version of the story — sixty-five centimetres here, a metre there, storm surges riding on top of a higher baseline — is the one that will arrive first.
Notable Quotes
Even under the highest-end scenarios, we do not foresee the geography changing within Cornwall and cannot speculate beyond our current projections.— Environment Agency
Sea level rise is accelerating incrementally over time rather than increasing at a steady rate, as previously thought.— NASA
The Hearth Conversation Another angle on the story
What's the actual point of showing a sixty-metre sea rise map? That's not going to happen in anyone's lifetime.
Probably not. But it makes the physics legible in a way that half a metre doesn't. You can see the shape of what's at stake.
Isn't that just alarmism dressed up as geography?
It depends on whether you treat it as a forecast or as a thought experiment. The map is honest about what it is — a slider tool, not a prediction.
So what's the number we should actually be paying attention to?
Somewhere between sixty-five centimetres and a metre by 2100, depending on whose modelling you trust. The Environment Agency's hard ceiling for planning purposes is 2.2 metres by 2115.
And Cornwall's geography doesn't change under any of those scenarios?
That's what the Environment Agency said. No new islands, no severed peninsulas — not within the timeframe they're willing to project.
Then why does the Lizard Peninsula show up as an island on the map at all?
Because the map goes far beyond what any agency will forecast. It's showing you the endpoint of total ice melt, not the next century.
What's the part of this story that doesn't get enough attention?
That 2100 isn't the end. The Royal Society is explicit — the sea keeps rising after that. The decisions we make now are shaping a coastline centuries out.
Does Cornwall have particular reason to worry compared to the rest of England?
Its coastline is long and irregular, with a lot of low-lying ground near the water. It's more exposed than most of the country to the near-term version of this problem.
Which is what, exactly?
Not islands. Just more flooding, more often, on a baseline that keeps creeping upward.