Our Nasa scientists have measured this in
How fast can this go? Right now, I think our best measure is what happened in the past. We know that, for instance, 14,000 years ago sea levels rose by 20m in 400 years – that is five metres in a century. This was towards the end of the last ice age, so there was more ice around. But, on the other hand, temperatures were not warming as fast as today.
How far can it go? The last time the world was three degrees warmer than today – which is what we expect later this century – sea levels were 25m higher. So that is what we can look forward to if we don’t act soon. None of the current climate and ice models predict this. But I prefer the evidence from the Earth’s history and my own eyes. I think sea-level rise is going to be the big issue soon, more even than warming itself.