The creeping menace

Remember the song… "New York, New York, is a helluva town / The Bronx is up and the Battery's down..."

Should we add the words …"A shame the city is going to drown…" ?

The problem is that much of New York is less than 5m above sea level. In fact many parts of the city are less than 2m above sea level and that includes large areas of Coney Island, Queens, Brooklyn, the Bronx and Staten Island, as well as neighboring cities in New Jersey. This places dwellings, port facilities, roads, bridges, subways, airports, industrial and other structures at risk of inundation when sea levels rise above 1m, less if accompanied by a winter storm surge or hurricane.

New York is not the only city threatened by flooding due to sea level rise. It will eventually affect Baltimore, Boston and Halifax, even Washington, threatening hundreds of thousands of houses, displacing millions of people and causing massive social and economic dislocation. US Federal, State and City governments are well aware of this threat but rightly feel it poses no short-term danger, while admitting it will occur.

Just as serious is the effect of sea level rise on the coastline. Bruuns Rule states that on average each 1cm of sea level rise results in about 1m of coastal recession. In other words, for each metre of sea level rise, the coastline is eroded by 100m threatening property, infrastructure and land located near and within 100m. of the existing coastline.

Risk of flooding is not going to suddenly become a looming danger. Sea level rise occurs very slowly and there should be plenty of warning of any impending threat. So why worry? New York and other great cities along America’s north-east coast are safe from flooding by rising sea level for at least a century, aren’t they? Well, probably not. If global warming continues unabated, flooding is likely to occur much sooner than previously thought.

Prior to the industrial revolution, sea level is estimated to have risen at about 0.2mm/year. In the 19th and 20th century, it reached an average rate of about 1.7 mm/year. From 1961 to 2003 the rate was 1.8 mm/year and increased to 3.1 mm/year from 1993 to 2003. This rate will continue to increase as ocean surface and air temperatures rise further, primarily due to the greenhouse and ice albedo feedback effects. These are bringing about acceleration in the four principal causes of sea level rise, which are:

· Melting of mountain based snow and ice, excluding polar ice caps, may elevate see level by 0.5-1m. and is expected to have fully melted by 2200.

Snow and ice permanently cover mountain ranges at higher altitudes and lower land at higher latitudes. Some of this cover melts seasonally or flows into glaciers which move it to the sea or a warmer altitude where it melts, producing water flows into lakes, riversand aquifers. These losses are normally compensated for by new snowfall and ice formation.

Global warming is causing this snow and ice to melt more quickly than it is being replaced and in many locations precipitation is falling as rain rather than snow. The result is that with few exceptions, the vast majority of the earths 150,000-160,000 mountain glaciers are in retreat and the area of land covered by snow and ice is shrinking.

Both events are occurring at an increasing rate for two reasons. First: solar energy hitherto reflected back into space is trapped by the greenhouse effect increasing air and surface temperatures. Second: land and sea which has lost its cover of snow or ice is now absorbing solar radiation, increasing their temperature.

· Melting of Ice Caps: