Sketch showing the total volume of sea level rise 1880-2009 compared to the volume of Hawaii

According to Republican Congressman Mo Brooks earlier this month, sea-level rise is caused by rocks falling into the sea, not thermal expansion. He's a member of the House of Representatives Science, Space and Technology Committee, and he told them that the California coastline and the White Cliffs of Dover tumble into the sea every year, and that contributes to sea-level rise:

"Every time you have that soil or rock or whatever it is that is deposited into the seas, that forces the sea levels to rise, because now you have less space in those oceans, because the bottom is moving up," (Reference: Science Magazine )

At Real World Visuals we think the World itself has a role to play in its own explanation. If Congressman Brooks is correct, what would that mean in terms of erosion? A quick calculation and visualisation can help.

Between 1880 and 2009, sea levels rose by 210 mm (Church, J.A. & White, N.J. Sea-Level Rise from the Late 19th to the Early 21st Century. Surveys in Geophysics (2011) 32: 585-602. Available online: link.springer.com/article/10.1007%2Fs10712-011-9119-1)

The total area of ocean is 361,219,073 km2, so a simple calculation tells us that each millimetre of sea-level rise corresponds to a volume of 361 km3. Multiply that number by 210mm and we get a volume of 75,856 km3.

So far so good, but how big is that, actually? How does it compare, for instance, to the volume of Hawaii?

The total area of the Hawaii Archipelago is 28,310 km2 and its mean elevation is 920 metres. That means that the total volume of Hawaii (above sea-level) is 26,045 km3. This means that sea level rise so far, is equivalent to the entire Hawaii archipelago falling into the sea not just once, but three times.

That's a lot of "soil or rock or whatever" and a lot more than the White Cliffs of Dover. We knocked up a very quick sketch with Google Earth to get a sense of scale.