Riddle of the sinking sea


THE Caspian Sea, with an area of some 150,000 sq. miles, is the largest enclosed body of water in the world, and earlier this century it caused great concern by threatening to disappear.

Investigations revealed that its mean level had fallen by nearly 6 ft. between 1933 and 1940, and the fall continued, albeit at a lesser rate, during the following three decades. The blame was put on the vast amounts of water that were being drawn for irrigation purposes from the rivers that feed into it. Around 1970 Soviet hydrologists devised a plan to rectify the situation.

Attention was focused on two great rivers, the Ob and the Yenesi, that meander northwards to deposit large quantities of fresh water into the Arctic Ocean. The idea was to dam these rivers, and at the same time provide the necessary artificial channels for the water to drain southwards into the Caspian Sea. This, it was felt, would not only prevent the imminent disappearance of the Caspian, but would also dramatically increase agricultural productivity by making fertile the arid steppes of Kazakhstan. Moreover, without the influx of fresh water from these great rivers, the Arctic Ocean would become progressively more salty it would be reluctant to freeze during the winter months, so that offshore oil reserves would become more easily exploitable, and the historic North West Passage would be navigable to shipping.

Climatologists in the western world, however, were aghast when they heard about the plan. They were of the view, that an Arctic Ocean iceless in the wintertime, being very much warmer than it is at present, would alter the circulation patterns of the atmosphere, with profound and unpredictable effects upon the climate of the entire northern hemisphere.

But then a strange thing happened. The shrinking of the Caspian Sea that had been in evidence for 40 years suddenly, and for no apparent reason, reversed itself in 1977. During the last 20 years, the level has increased by more than 8 ft., bringing it back almost to that of 1933. Why this should have happened is something of a mystery; it is known to be directly related to greater rainfall and lower evaporation in the catchment area, and these in turn are believed to be connected to subtle changes in the airflow patterns on the North Atlantic, but no connection to any straightforward mechanism, like sunspot numbers or the rise in global temperatures, has been detected.

In any event, the Russians quickly abandoned notions of diverting any rivers, and climatologists around the world relaxed again.