Global Warming: How High Will the Sea Rise?

There has been much discussion about just how high the sea level is expected to rise because of global warming. According to a report prepared for the British Irish Council in 2003, it was suggested that the rise in the next 100 years would be somewhere between 9 cm to 69 cm. In other words, the worst case scenario would be just over 2 feet. Since then, estimates have got a little larger as we have realised that glaciers are melting at a much faster rate around the world. Lake Mead in America has suffered 8 consecutive years of drought because there just is not enough snow falling in the Rocky Mountains. Bolivia is facing a crisis as a glacier that has provided water for the population for the whole of their known history is now receding into nothingness. The Greenland glacier, which holds 10% of the world's fresh water and would cause a sea level increase of 23 feet on its own, has now receded to the point that people are starting to farm the land that was underneath.

But I think the most accurate way of working out how bad it could be is to look at the past to other interglacial periods. My home island of Jersey has evidence of three such periods in the forms of fossil beaches. But I am afraid the news is not good. The beaches are at 8 metres, 18 metres and 30 metres above present sea level! 30 metres - that is 98 feet. Now there is some discussion as to whether that is because the sea rose that high or if the land was lower because of the pressure of glaciers pushing it down. But 98 feet?!! It is hard for me to take in just how much extra water an increase of 98 feet over the whole world would represent and how the map of the world would change. I know one thing, most of Jersey would be under water. I would be amazed if half of the island remained.

Even 8 metres is horrific. That is about 27 feet which is not much more than the Greenland glacier could do on its own. That would easily take out a third of Jersey. It would also signal the end of London, Manhattan and, of course, Venice. In fact, I would suggest that most of the world's cities are below the 27 feet limit.

Not only is the sea level rising beause there is more water, there is also the nightmare that is called thermal expansion. As water warms, it expands. It may only be a small amount but given the size of the oceans, even a small change will produce large results. What effect this will have is still unclear because it will depend on whether the Atlantic conveyor switches off or not

The problem with increased sea level is that rivers find it harder to discharge their water into the sea. Whenever this happns, it causes flooding. This is the reason why Bangladesh regularly floods. A 27 foot increase in sea level would force water to back up and flood the river valleys resulting in the loss of even more land and because it is a permanent increase, it will cause a permanent flood. Most of the world's population live near rivers and the sea therefore most of the world's population are going to to have to find somewhere else to live.

I was personally amazed to find out that the raised beaches of Jersey had been known about and discussed since 1893 (Quarterly Journal of the Geological Society; 1893; v. 49; issue.1-4; p. 523-530) but conveniently forgotten in the 20th and 21st centuries.

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