Rolling back the rising waters

Press, 13 May 1986, Page 10

Rolling back the rising waters

From “The Economist,” London

Throughout this century, the weather has grown erratically wanner. At the same time, the sea level has risen, also erratically, at an average rate of more than one millimetre a year. The two developments are connected. Not only does water expand when warmed, but a warmer climate makes glaciers melt faster, returning to the sea moisture that has remained locked into ice caps for generations.

A millimetre a year may not sound much, but a rising sea level ought to worry Dutchmen and others who live near lowlying coasts. If the alarmists are right, man’s habit of burning fossil fuels to make “greenhouse” (that is, heat-trapping) gases is accelerating the warming of the atmosphere, then sea level could rise 3.5 metres by 2100.

The human race need not get its feet wet. Two New York scientists (no doubt with visions of paddling to work down Fifth Avenue) have recently published an ingenious analysis of how to lower sea level by building reservoirs and flooding depressions in the earth’s surface.

Dr Walter Newman at City University of New York and Dr Rhodes Fairbridge of Columbia University, writing in the journal “Nature,” calculate that the reservoirs man has built since 1932 have caused a 26-year lag in the rising sea level.

Their arithmetic goes thus. The sea level has risen by 1.25 mm or 300 cubic miles a year since 1932. The 107 largest reservoirs in the world hold, altogether, nearly 2000 cubic miles of water. Small reservoirs hold probably as much again. Irrigation projects have diverted water that would normally go into the sea into dry soil at the rate of about 80 cubic miles a year, or 4400 cubic miles altogether. That makes 8000 cubic miles now on land that would otherwise be In the sea, or 32.5 mm of potential sea level rise.

Of course, this is rough and ready arithmetic. Other factors should be taken into account. More reservoirs mean more evaporation, and so more rain, some of which gets to the sea. Much of the water extracted from underground aquifers, such as the great Ogalla aquifer on which many Texas farmers depend, gets to sea now that never did before. A warmer climate might make more snow fall than melt in Antarctica, locking up more ice.

None the less, by building reservoirs and irrigation schemes, man has already cancelled out nearly half of the rise of sea level he would otherwise have caused.

With a little effort, say Dr Newman and Dr Fairbridge, he could keep sea level almost steady for a good few decades

yet Only then would he have to start building dykes or evacuating coastal cities. Several big schemes are being mooted that would help lower sea level. The biggest and most practical is the long-debated Russian scheme to divert parts of the three great Siberian rivers, the Ob, Yenisey and Lena, that carry between them 1000 cubic miles of water away into the Arctic Ocean each year, south into the Aral and Caspian seas. The Caspian could do with some water. It is nearly 100 feet below sea level and shrinking all the time. Raising it 30 feet would store 2750 cubic miles of water or eight years’ worth of sea rise. The Aral sea is all but dry. The aim of the Russian schemes is not, of course, to stop Holland sinking beneath the waves. It is to open up desert for farming with the river water. But that is not going to happen, for the time being at least. The cost and a Gorbachevian distrust of vast engineering projects, plus ecological concerns at the possible effects on the Arctic have combined to persuade the Russian Government to shelve it. Then there are the earth’s depressions. Five of them — the Imperial Valley in California, the Qattara Depression in Egypt, the Dead Sea, the Salina Gaulicho of Argentina and the Danakil Depression in Ethiopia — are big enough to hold more than 600 cubic miles each and close enough to the sea to be flooded with seawater.

The Israelis have long thought

of generating hydroelectric power from Mediterranean water coursing downhill through a tunnel into the Dead Sea. The snag, as so often with these schemes, is that this threatens to disturb the ecological balance

and to lose local people their land. And people made landless are not any happier when they are told that shallow inland seas often provide fertile fishing grounds. Copyright, “The Economist.”