Just under a foot may not sound all that much if thought about from the perspective of going for a paddle in the sea with one’s trousers rolled up.
However, the volume of water required to add that height to all the world’s oceans – which cover some 363 million square kilometres – is truly vast and, as we know, water has a tendency to slosh around, which is why even relatively small increases can make storm surges and flooding much worse.
The rate of increase has also been quickening. Between 1901 and 1971, it averaged 1.3mm a year; between 1971 and 2006, it was 1.9mm; and between 2006 and 2018, it was 3.7mm. The main causes are melting ice, much of it from Greenland and the Antarctic, and the expansion of the water as the oceans get warmer.
And, according to the IPCC report, it is “virtually certain that global mean sea level will continue to rise over the 21st century”.
It estimated there will be a further increase of between 28 and 55cm by 2100 if greenhouse gas emissions are kept “very low”, 44 to 76cm in an intermediate emissions scenario, and 63cm to 1.01 metres with a “very high” one.
However the report added that “approaching two metres by 2100 and five metres by 2150 under a very high greenhouse gas emissions scenario cannot be ruled out due to deep uncertainty in ice sheet processes”.
Worldwide, more than 600 million people currently live in coastal areas less than 10 metres above sea level in places like New York, Miami, Venice, Rotterdam, Jakarta, Bangkok, and Alexandria.
A metre of sea level rise could submerge a vast area of land in eastern England, potentially turning Peterborough and Cambridge into seaside towns.
Despite this insidious, steadily growing threat, global carbon emissions continue to go up as the nations of the world continue to fail to rise to the challenge of protecting themselves against it.
The Cop26 climate summit in Glasgow is a chance to change course, to minimise the damage. Future generations will curse us if we do not.