Doing the maths

From Science

Brooks then said that erosion plays a significant role in sea-level rise, which is not an idea embraced by mainstream climate researchers. He said the California coastline and the White Cliffs of Dover tumble into the sea every year, and that contributes to sea-level rise. He also said that silt washing into the ocean from the world’s major rivers, including the Mississippi, the Amazon and the Nile, is contributing to sea-level rise.

It’s true that this idea is not embraced by mainstream researchers. But there’s more than that. Unlike some of the more complex and subtle uncertainties in the rate and causes of sea level rise, this argument is not embraced by people who can use Google and a calculator.

The main contribution of the land to the sea floor is the 20 billion tons or so of silt from the world’s rivers.  Soil weighs in at between 1 and 2 tons per cubic meter; rock mostly between 2 and 3. Let’s be generous and call it 20 billion cubic metres. Not all of that ends up in the ocean — lots of it goes to coastal wetlands and deltas — but we’re messing them up too, so again let’s be generous and say it all ends up underwater.

The ocean area is 360 billion square kilometres, so about 360 million billion square metres. It would take 360 million billion cubic metres of added stuff to raise sea levels 1 metre — actually more, since the ocean area would expand, which is actually the main issue with sea level rise, but again we’ll be generous and say only 360 million billion. Dividing by 20 billion gives 0.000055 metres or 0.05 millimetres.  Actual sea level rise over the whole 20th century averaged 1.8mm/year, about 30 times more.