Of all the known unknowns in climate science, the increased risk of coastal flooding brought about by rising sea levels and melting polar ice has proved one of the most intractable
It is also arguably one of the most important issues of the modern era given that in Europe alone some 70 million people live near the coastline where there are economic assets worth between £500bn and £1,000bn.
Around 10 million people each year worldwide are currently affected by coastal flooding. Even without any further rise in sea levels – which is impossible – this number is likely to triple as more and more people migrate to the coastal regions of the world.
Sea level is not a simple problem. For a start, a rise in global sea level is not uniform. It will actually decrease in parts of the world, such as Greenland and Antarctica, where melting ice will change the regional gravitational fields that exert a pull on the surrounding ocean.
Britain and the rest of Europe will see sea-level rises that are about 10 or 20 per cent below the global mean. Tropical regions on the other hand will see the increases well above average, especially in the equatorial Pacific Ocean where some low-lying island states will be inundated by the sea.
The last report of the UN’s Intergovernmental Panel on Climate Change had to use much guesswork to assess how sea levels will change this century. The latest effort by the Ice-2-Sea programme, specifically established for the task, has tried to clarify the many unknowns for the next IPCC report due later this year.
These uncertainties are why the range for mean sea-level rise is so wide, anything from 3.5cm to 36.8cm for the contribution from melting ice. Thermal expansion of the warmer oceans will add about as much again, making the latest predictions of sea-levels slightly more pessimistic than the last IPCC report.
Even if we stop CO2 emissions tomorrow, global sea-level rise caused by melting ice will continue due to the inertia of the world’s climate. But the earlier we begin to curb CO2, the better it will be for our coastlines.