How much will the sea level rise?

More than 100 million people around the world live on land that is only one metre above the current sea level.

In Scotland, it is predicted that sea levels will rise by up to 600mm around the mainland by the 2080s, with local variations due to land movement. Scottish cities, including Edinburgh, coastal towns and villages, the Outer Hebrides and Northern Isles will all be at risk from flooding.

The Scottish Environmental Protection Agency (SEPA) noted in its 2006 State of the Environment report that all Scottish mainland tide gauges have recorded a sea level rise over the long term. The longest individual record indicates an average sea level rise of 0.6mm per year at Aberdeen since 1862.

Sea level rise increases the risk of flooding of coastal towns and leads to the erosion of natural habitats and loss of biodiversity.

The Scottish Climate Change Impacts Partnership (SCCIP) website includes data on climate trends and impacts in Scotland.

In the ten years from 1993 to 2003, global sea levels rose by an average of 3mm per year. The total rise in the 20th century is estimated to have been 170mm.

While these kinds of increases may seem small, the 170mm recorded is already affecting many parts of the world, such as Pacific Islands and farming areas in river deltas. The effect of the projected increases will be even more disastrous.

In the longer term, global sea level rise is predicted to increase by between 90mm and 880mm by 2100 depending on greenhouse gas emissions.

London and the Thames Barrier

The Thames Barrier was built in 1982 to prevent tidal flooding of central London. At the current likely rate of sea level rise between 2030 and 2050 the Thames Barrage will be overwhelmed. The UK Government is considering options for a second larger barrier to address this issue.

Scientists predict that global sea level rise will have two main sources. Firstly, as the oceans heat up the water expands. At present this thermal expansion accounts for about half of the observed increase in sea level. The other cause is melting land ice from glaciers and ice caps. The rate of melt and the volumes of water locked within these sources is uncertain and is a cause for concern.

Sea Ice and Land Ice

While sea ice is melting in both the Arctic and Antarctic, it is land ice that contributes to sea level rise. This is because sea ice is already displacing its mass, so when it melts it takes up more or less the same space. Land ice contributes new water to the seas, resulting in sea level rise.

In recent years, ice shelves have broken off huge ice sheets in Antarctica and Greenland. The ways in which they are melting is only now beginning to be understood fully enough to allow estimates of how fast this melt is occuring and how much this will affect sea levels. Because of this uncertainly they have not been included in the scenarios discussed so far.

If they melt as fast as is now thought to be possible sea levels could rise dramatically over the next century, flooding many of the world’s major cities and much of the world’s most productive farmland.

'What do we do with a city like Melbourne once the rainfall patterns change, once the extreme weather events start kicking in, and once sea level rise starts happening very seriously? There’s two words to explain it - we’ll just abandon it - and cities like London that have been there for a thousand years will have to be abandoned, and cities like New York, Amsterdam.'
Tim Flannery, author of ‘We Are the Weathermakers’, talking to secondary school students in Melbourne, Australia

Photo credit: (above) twoblueday

Available for use under Creative Commons Attribution 2.0 conditions.

Photo credit: (below) Tracey Dixon.