Between denial and the deep blue (rising) sea

Adam Morton in the Age (Australia): It is called the Bruun rule, and it works like this. For every centimetre the sea level increases, it says there is a decent chance of the shoreline retreating between 50 centimetres and a metre. If the sea should rise by a metre - which some scientists say is possible this century if ice sheets melt with global warming - that would mean 50 to 100 metres of coast swallowed by the ocean.

The Bruun rule is only a rough guide, and does not recognise many of the complexities at play; for a start, it assumes a flattish, sandy coastline with steady wave formation. But, as a rule of thumb, it gives some insight into what scientists find can be a difficult idea to get across - that changes being projected for the ocean would be much more damaging than they seem at first blush.

The sea is rising: steadily if not visibly. Scientists say the average pace around the globe is three millimetres a year, or 30 centimetres a century at the current rate. … How these estimates were reached, and whether the assumptions underpinning them still stand up, is explained in a new book. Understanding Sea-Level in Rise and Variability brings together the work of more than 90 researchers. Its lead editor, CSIRO oceanographer Dr John Church, says that by including the most recent peer-reviewed science it provides greater certainty than the latest IPCC report.

The book quantifies the causes of recent sea-level rise. About 40 per cent has come from thermal expansion - the increase in the size of water molecules as it gets hotter. Another 40 per cent is from melting ice caps, and the diminishing glaciers in Alaska, Patagonia, the Himalayas and the Antarctic Peninsula. The remaining 20 per cent is run-off from water storages and aquifers - and the wildcard of the ice sheets.

…Church says senior bureaucrats and many politicians understand the need to act, but sees a lack of urgency. ''This is not based on a belief system. It is about trying to understand what the observations are telling us,'' he says. ''There are about 140 million people living within one metre of high-tide levels around the world, and roughly $1 trillion of infrastructure in that region. Those assets, those people, are already at risk from storm surges, inundation and erosion, and increasingly will be so.''

High water in Venice, shot by EVenise, Wikimedia Commons, under the Creative CommonsAttribution-Share Alike 3.0 Unported license