Tom Arup, The Age Sydney Morning Herald 9 Nov 15;
Hundreds of millions of people around the world are living in places that could eventually be submerged by rising sea levels triggered by unchecked climate change, new global maps suggest.
An estimated 627 million people live in these places, including about 1.9 million in Australia and many more in the world's great metropolises such as Tokyo, New York and Shanghai.
The rising seas won't happen overnight, nor in anybody's current lifetime. The global mapping project, carried out by the US group Climate Central, is based on huge sea-level rises that would not emerge for another 200 to 2000 years.
But a report that accompanies the maps, released on Monday, says this future would be locked in if global warming reached four degrees by 2100 - considered likely if the current level of emissions continued unabated.
The project is based on a scientific paper published in the Proceedings of the National Academy of Sciences of the USA in October. That analysis - carried out by researchers at Climate Central - found that four degrees of warming could lock-in 8.9 metres of long-term sea level rise in the centuries to follow.
If warming was held to two degrees by strong emissions cuts - the goal of a new global climate agreement countries are negotiating through the United Nations - then the rise would be more like 4.7 metres. About 280 million people live in areas below that watermark.
Across Australia, the analysis finds there are about 1.9 million people living in areas that would be submerged if there was an 8.9 metre rise in sea level. At 4.7 metres, it is 668,000 people.
In central Melbourne, the maps based on what is locked in with four degrees of warming suggests significant inundation of prized bayside suburbs and throughout Docklands.
The actual number of people who would be affected is fairly speculative given the very long timeframes at play. These numbers do not factor in preventative measures cities might take in the meantime to counteract rising seas. Nor does it consider how populations will move and grow.
Sea level rise as a result of global warming comes from the thermal expansion of the oceans and the melting of glaciers. But the biggest potential rises depend on the long-term response of massive ice sheets in Antarctica and Greenland, for which there is significant scientific uncertainty.
For that reason scientists have been largely conservative in their projections. In 2013, the UN Intergovernmental Panel on Climate Change reported in its last major assessment a projected sea-level rise of at worst 0.82 metres out to 2100 with unchecked emissions.
But more recently a number of studies have begun to explore what might happen after the end of this century. One recent example is an Australian-led study that found if ice shelves protecting the Antarctic sheets from the ocean were lost, then it would unlock thousands of years of unstoppable contributions to sea level rise.
