Science - June 26, 2012

Sea level keeps rising, no matter what

The sea level will rise by 25 centimetres by the middle of this century, regardless of what we do. Climate measures will only have some effect afterwards.

This prediction is made from the latest calculations on the rise in the sea level, supervised by Michiel Schaeffer (Environmental Systems Analysis Group) in Wageningen. The results are published in the online version of Nature Climate Change. The article shows the effects of climate change on the sea level. One thing is crystal clear: the sea level will continue to rise, no matter what. Even if there were no more CO2 emissions from now on, hypothetically speaking, the speed at which the water rises in the coming decade will still increase. By the middle of this century, this rise will be six millimetres per year, twice as much as that we are now faced with. This is due to the climate lag effect of the amount of CO2 which was released into the atmosphere in the recent past.
Promises
The effects of climate policies will only be somewhat visible towards the end of this century. If all the promises and incomplete agreements reached at the various world climate conferences were carried out, the sea level would rise by only about one metre. Zero emission would bring this down to 59 centimetres. Therefore, a rise of 40 centimetres can, in theory, be avoided. And this is the best we can do.
On the other hand, climate policies would be much more effective if the researchers look beyond this century. The sea level would have risen by many metres by then. A successful climate policy - global warming kept to less than two degrees Celsius - would limit the sea level rise by the year 2300 to between 1.5 to 4.2 metres. In that case, the most probable scenario would be a rise of 2.7 metres.
2300
Estimates for the long term vary somewhat. One reason is because scientists do not know exactly how global warming will affect the ice in Greenland and Antarctica. The latest statistics show a lower sea level rise than that reached by the Delta committee in 2008. It was predicted then that the water level rise along the Dutch coast by 2100 would be 1.3 metres. This is 30 centimetres more than the current figures. The researchers attribute this difference to the fact that the effects of successful climate policy have been taken into account.