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Bullet pointBullet pointBullet point   Forecast for big sea level rise   Bullet pointBullet pointBullet point

Adapted from a BBC online articles: Tuesday 15 April 2008, 22 January 2008, 6 June 2007

Sea levels could rise by up to one-and-a-half metres by the end of this century, according to a new scientific analysis.  The new analysis comes from a UK/Finnish team which has built a computer model linking temperatures to sea levels for the last two millennia.

Bangladeshis in flood water  
People in low-lying poor nations, such as Bangladesh, are at most risk
  
80 to 90% of Bangladesh is within a metre or so of sea level. So if you live in the Ganges delta, you're in a lot of trouble.

Dr Simon Holgate, Proudman Oceanographic Laboratory (POL), near Liverpool, UK.

A sea level rise of this size would change the shape of coastlines around the globe. And it would have a major impact on low-lying countries such as Bangladesh and on many others - such as the high-flying city bankers in New York. More than half of the world's population have made their home in coastal regions.

And while cities such as London, New York and Singapore are likely to spend billions on protecting inhabitants from flooding, many small island nations are at risk of disappearing beneath the waves.

Although there is still a debate among scientists about how much waters will go up by the end of the 21st Century, there is general agreement that the average sea surface is rising, and that there is a complex array of factors driving the increase, including:

  • Thermal expansion - the greenhouse effect heats the ocean, causing it to expand
  • Ice melt - rising air temperatures cause mountain glaciers and ice sheets to melt, sending the resulting melt water into the sea
  • Ocean current variations - pan-ocean currents, for example the Gulf Stream, are the main way that heat energy is transported from equatorial waters to cooler higher latitudes. However, these are subject to natural variations. Probably the best-known system is El Nino, which moves vast quantities of water from one side of the southern Pacific to the other every three to four years
  • Topography - the combination of ocean currents and atmospheric pressure systems means that the oceans are not flat. Data gathered by satellites show height variations that exceed two metres

"For the past 2,000 years, the [global average] sea level was very stable: it only varied by about 20cm," said Svetlana Jevrejeva from the Proudman Oceanographic Laboratory (POL), near Liverpool, UK. "But by the end of the century, we predict it will rise by between 0.8m and 1.5m. "The rapid rise in the coming years is associated with the rapid melting of ice sheets."

The computer-generated image below shows the variation in sea levels using date obtained from a satellite. Note that the ocean surface is not flat - it is actually uneven due to several factors, such as pressure systems. Another method of gathering data on sea levels is the use of a network of monitoring stations.

Graohic showing sea level variations
Sea surface height data gathered by Jason-1 during a 10-day mapping cycle. The white area in the West Pacific Ocean shows the largest increase, while the purple and pink areas around the Southern Ocean mark the greatest decrease.

 

Diagram of Jason-2 satellite
Diagram of sea level monitoring station
Photo of Eureka Glacier

Diagram of Jason-2, a low-orbit satellite for measuring ocean topography.

1. Advance Microwave Radiometer (AMR) - measures signal delay caused by water vapour
2. GPS antennas - ensures precise orbit path
3. Poseidon-3 altimeter - measures sea level
4. Doris antenna - tracking and positioning control
5. Laser Retroreflector Array (LRA) - tracks and calibrates measurements
6. Mass: 525kg (1,155lb)
7. Power generation: 511 watts
8. Height: 3m (9ft 8in)
9. Orbit: 1,338km (831 miles)
10. Launch date: June 2008)

(Source: Eumetsat, Cnes, Nasa)

Diagram of Australian sea level monitoring station

 

 

 

SIMPLY THE BEST - THAT'S THE SEA CADETS !

The Eureka Glacier lit by the midnight Sun.

British Antarctic Survey (BAS) scientists used Europe's ERS-1 and -2 spacecraft to track the flow rate of over 300 "flowing" glaciers. The satellite data confirmed that Antarctic glaciers are flowing faster than before.