Coastal cities face uncertain sea levels

Calving of a huge ice berg off the Jakobshavn glacier in Greeland, June 5, 2007. Credit: Jason Amundson, University of Alaska, Fairbanks. The title of the lecture was "A Tale of Two Cities, and of Climate Change: Future sea level projections in New York and Abu Dhabi". But if any of the audience were hoping to learn when those cities would vanish beneath the waves, they were destined for disappointment. According to Professor David Holland of the New York University Courant Institute of Mathematical Studies , there are things about climate we know, others we can credibly extrapolate, and still others about which we know too little to make even meaningful guesses. The last class includes the magnitute and rate of future changes in sea level. "There is no credible projection about when and how much sea level will change," Dr Holland, who is also the director of NYU's Centre for Atmospheric and Oceanic Sciences (CAOS), said during his lecture yesterday in Abu Dhabi. In other words, anyone who predicts that with an X degree rise in temperature, the sea level will rise by Y centimetres within Z years is talking through his or her hat. The Intergovernmental Panel on Climate Change predictions that sea level will rise between 18 and 59cm by 2100? Not worth the paper they are written on. This is not what we are used to hearing from western governments, environmentalists and the popular press, so how does Dr Holland justify his assertion? He agrees with most climate change activists that the warmer the planet is, the more of its ice sheets will melt. Where he parts company with the popular consensus is on whether it is possible to infer from historical data and the current climate change models the speed at which sea levels will increase. Rising air temperature is not the primary cause of huge chunks of ice falling into the sea along the coasts of Greenland and Antarctica, . Instead, the main culprits are deep, warm, salty ocean currents that from time to time slam into the two ice sheets left over from the Earth's last glacial period. Think of a glass of water with ice cubes, and of how much quicker the ice melts if the contents are stirred than if they are left to sit. According to Dr Holland, there are two locations at which ice is falling into the ocean and driving up the planet's overall sea level faster than anywhere else on Earth. One is in Greenland. The other is in western Antarctica. At Jakobshavn, Dr Holland's researchers have shown, from their own measurements and fishermen's records, that the warm current crossing the Atlantic from southwest to northeast has for the past decade been turning back on itself, forming an eddy that has been slamming into the coast of Greenland. The ocean current changed its path a year after a sudden change in North Atlantic wind patterns, which fits with climatological theories that oceans respond to what is happening in the atmosphere, and vice-versa. At Pine Island, the CAOS researchers have just begun to collect data, and because of the remoteness of the location and harsh weather conditions, the work is progressing at a snail's pace. Historical data from the site is nonexistent. Climatological models of the deep, warm ocean current that encircles Antarctica, however, predict it should spiral in to hit the western Antarctic's marine ice shelf at exactly the location of Pine Island. It is possible, Dr Holland concedes, that increased burning of fossil fuels and resulting greenhouse gas emissions of the past century have caused or at least contributed to changes in wind patterns that in turn cause ocean currents to shift course and accelerate the melting of ice sheets. On the other hand, geologists have found records of many previous shifts in wind patterns. There seem to be large-scale climatological oscillations taking place over historic and geological time, but atmospheric scientists do not understand the phenomena well enough in most cases to predict them. The bottom line is that no one knows at present just how sea level changes will play out over our lifetimes, or even those of our grandchildren. So should Abu Dhabi residents stop worrying about future inundation? Unfortunately, Dr Holland's worst-case scenario, which he admits is no more than an educated "gut-feeling", is for a seven to eight metre rise in global sea level over the next 200 years. That would be far more catastrophic than the IPPC's worst-case prediction. On the other hand, nothing much may happen, which puts urban planners for major coastal cities around the world in an untenable position of deciding wether to pour tens of billions of dollars into coastal defences that may not be needed. In Abu Dhabi's case, should the Government be thinking of moving the emirate's capital inland to its original seat, Al Ain? How should Abu Dhabi's vital coastal power and water desalination plants be protected? And what about the big industrial complexes on the Gulf coast? In Dubai, what will happen to the huge Jebel Ali container port? Could Dubai's residents be reduced to eking out a living from offering well-heeled travellers tours of "the Atlantis of the Gulf"? The point is that science cannot currently provide the answers, although it may be able to do so in future. More data are needed, and we had better get cracking on making the required but difficult observations. "NYU wants to contribute. It's going to take a long time, but if we don't start, we won't get there," Dr Holland said yesterday. "A place like Abu Dhabi, if it really wants to make a contribution, could take forward the observational network by establishing a sea-level centre. It could contribute to global and regional understanding of sea level," he added.