Sky’s Thomas Moore is on a mission to the bottom of the planet to find out why what happens there affects us all.
At the start of the last century, the water was creeping upwards at just over 1mm a year. Now it’s 3mm – and accelerating. It doesn’t sound much, unless you live on a low lying island, like the Maldives or Kiribati, already losing land to the sea.
But scientists can’t rule out a 2m (6.5ft) rise by the end of the century. Spring tides and storm surges could drive up the level even more.
New York, Miami, Calcutta, Lagos and other great cities could be flooded. One billion people could be forced to move.
That could already be baked in to our future, regardless of efforts to reduce global emissions of greenhouse gases.
Three million years ago carbon dioxide levels were much the same as they are today. Temperatures were a degree or two warmer. But sea levels were 20m to 25m higher.