Sea Level Rise
As temperatures increase this causes sea levels to rise by two methods. Firstly glaciers and ice sheets melt which increases freshwater input into the oceans. And secondly, as oceans warm they increase in volume through thermal expansion. The latest IPCC report estimated that globally averaged ocean surface warming could result in a sea level rise of up to 59cm by 2100; this projection does not include uncertainties of carbon-cycle feedbacks such as glacial and ice cap melting.
Sea level rise represents a significant threat to millions of people around the world. For instance over 17 million people in Bangladesh live at an elevation of less than 1.5m above sea level. The land they live on is the most fertile in the country and provides half of Bangladesh’s rice crop to a population of 170 million people. A sea level rise of this level would prove catastrophic and result in the migration of millions of people.
The Pacific island nation of Tuvalu has already drawn up evacuation plans with New Zealand amid concerns of coastal flooding.
The threat is not just confined to the poorer nations. £2.9 billion is being spent on flood protection for Venice which now experiences some level of flooding 200 days of every year compared to only 7 at the beginning of the century. There are similar concerns in London over the effectiveness of the Thames Barrier and its ability to cope with rising sea levels. In the previous five years the barrier has been used 55 times but in the five years before that it was used 12 times.
The greatest threat from sea level rise is linked to the stability of the world’s largest ice-masses. If the Greenland ice sheet were to melt it would raise sea level by 7 metres. Worryingly, new research has indicated that the ice sheet could disappear with a warming of as little as 2.7°C. Sir David King, chief scientific advisor to the government, recently stated that he thought a 3°C rise was likely. There is also further concern that irreversible melting of the ice sheet could occur with only a 20% reduction in its present size.
The above graph, courtesy of the IPCC, shows projected sea level rise to 2100. It represents a range of different scenarios taking into account industrial activities of the developing world, future land use change and the uptake of new technologies.