Celebrated climate scientist James Hansen has blunt tidings in the last edition of New Scientist: “I find it almost inconceivable that ‘business as usual’ climate change will not result in a rise in sea level measured in metres within a century.”
(Wondering how a 5 metre rise would affect you? This excellent hacked version of Google Maps has the answer.)
Bottom line on what needs to be done to avoid this, according to Hansen:
The global community must aim to restrict any further global warming to less than 1 °C above the temperature in 2000. This implies a CO2 limit of about 450 parts per million or less.
Hansen’s projection of whole metres before 2100 is much more negative than the latest IPCC figures – which project sea level rise of between 18 and 59 centimetres by the end of the century. But, Hansen argues, the IPCC consensus overlooks a crucial factor.
What many people do not realise is that [IPCC] models generally include only fast feedback processes: changes in sea ice, clouds, water vapour and aerosols. Actual global warming would be greater as slow feedbacks come into play: increased vegetation at high latitudes, ice sheet shrinkage and further greenhouse gas emissions from the land and sea in response to global warming.
Once these missing elements are factored in, he continues,
…the primary issue is whether global warming will reach a level such that ice sheets begin to disintegrate in a rapid, non-linear fashion on West Antarctica, Greenland or both. Once well under way, such a collapse might be impossible to stop, because there are multiple positive feedbacks. In that event, a sea level rise of several metres at least would be expected. As an example, let us say that ice sheet melting adds 1 centimetre to sea level for the decade 2005 to 2015, and that this doubles each decade until the West Antarctic ice sheet is largely depleted. This would yield a rise in sea level of more than 5 metres by 2095.
As a New Scientist editorial comment notes,
While a mere 2 per cent of the world’s land is less than 10 metres above the mid-tide sea level, it is home to
10 per cent of the world’s population – 630 million and counting – and much valuable property and vital infrastructure. Without mega-engineering projects to protect them, a 5-metre rise would inundate large parts of many cities – including New York, London, Sydney, Vancouver, Mumbai and Tokyo – and leave surrounding areas vulnerable to storm surges. In Florida, Louisiana, the Netherlands, Bangladesh and elsewhere, whole regions and cities may vanish. China’s economic powerhouse, Shanghai, has an average elevation of just 4 metres.
