Measuring and accounting for sea-level rise

[The Magic Pudding]

John Church explains how sea-level is measured. One method uses tide gauges. The other employs a satellite 1,300 km above the earth. Sea-level is currently rising at the average rate of 3.1 mm/year. This compares with the average rise for the 20th century of 1.7 mm/year. The higher sea-level is partly explained by thermal expansion. Hotter sea water takes up more volume than colder water. As the Earth is warming, so too is the ocean and so this contributes to sea-level rise. The other factor is more water in the ocean as the result of melting ice from sheets at the poles and from glaciers.

Interestingly, just over the last two years Australia has experienced major floods. Several other areas around the world have also experienced major floods. As a result of this, sea-level actually fell, it fell by about 5 mm, and you can measure this both from the satellites and also from the gravity measurements which determine the mass stored in the ocean and the mass stored on land. And these agree that the prime reason for the sea-level fall is transferring of mass from the oceans to the land. We are actually seeing sea-level coming back to the trendline as the water runs off from the land back into the ocean.

I'm impressed that scientists can measure a sea level fall due to floods.
That's quite an impressive piece of accounting.

There is audio and transcript available.

[Tank]

There was a Horizon programme on weird weather last week and the fact that stuck in my mind was that the 1C increase of global temperature allows the atmosphere to hold on average 4% more water. That's a lot of water! And it's got to come back out somewhere. In addition that 4% isn't evenly distributed. Compounding this is the change in weather patterns leads to lots of water arriving where it hasn't done before.