The creeping menace

Thermal expansion of seawater occurs as a result of rising ambient temperatures, particularly those affecting the top 500m. It is regarded as having contributed up to 50 percent of the rise in sea level that has occurred over the last century.

Scientific consensus is that on current levels of green-house gas emissions temperatures could rise by 5-6C and that to limit warming to 2C, anthropomorphic greenhouse gas emissions must peak by 2015 and reduce to near zero by 2050. Refusal of the largest emitters, the USA, China, India and Japan to commit to those reductions makes a global warming limit of 2C by 2100 impossible.

Given these considerations, rise in sea level by 2100 due solely to thermal expansion is estimated to be between, at best 75mm and 255mm at worst.

Extreme climate events which have a significant effect on local sea level include storm surges, king tides, cyclones/hurricanes and temperature increase (and decrease), particularly in polar regions where temperature rise tends to be double the global average. Increased sea temperature is likely to increase the incidence of hurricanes and their severity.

Expert evidence given to the Australian House of Representatives Committee on Climate Change, paragraph 2.60-64, warn that as sea level rises, so does the incidence of dangerous climate events increasing the effects of sea level. An increase in sea level of 0.2m is likely to result in a 10 fold increase in the number of severe climate events. An increase of 0.5m could increase the number of such events to one a day, vastly exacerbating the dangers arising from elevated sea level, causing it to rise further - a feedback situation.

Taking into account 2009 National Centre for Atmospheric Research estimates, it may well be at least 25-50cm higher along the NE coast of America. In summary, by 2050 many of the great cities of the New England States and all of their coastline could be exposed to a rise of 1.0-1.4m in sea level.

Expert evidence given to the Committee concluded that global sea level could rise by 1.4m by 2100 but that it could be substantially higher (para 24.9). This paper concludes that on the basis of currently available data global sea level is likely to rise by at least 0.9m by 2050 and probably by over 2.0m by 2100.

It would be imprudent for governments and other organisations to assume that planning and implementation of mitigating action is not urgent. It can not wait until the latter half of the century because the scientific consensus on sea levels rising by 1.1m by 2100 is likely to become a reality 50 years sooner.

New York, New York is a helluva town and it would be catastrophic if it were to drown. But it will, within 40-50 years, unless global action is taken to ensure greenhouse gas emissions reach a peak no later than 2015 and increase in pre-industrial temperature is kept below 2C. Those outcomes seem unlikely.