The Caspian Sea, with an area of some 150,000 square miles, is the largest enclosed body of water on our planet. As the second World War approached, it caused great concern by threatening to disappear.
Investigations revealed that its mean level had fallen by nearly six feet between 1933 and 1940, and the fall continued, albeit at a lesser rate, during the following three decades. This, of course, was very worrying for the usual environmental reasons, but more to the point was the fact that as the lake got saltier and smaller, its productivity in sturgeon was reduced, and the world's supply of caviare was threatened.
The reason, it was supposed, was that vast amounts of water were being drawn for irrigation purposes from the rivers that feed into the Caspian Sea, resulting in a decrease in water levels in the lake. Around 1970, however, Soviet hydrologists devised a five-year plan to rectify the situation.
Their 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 to provide the necessary artificial channels for the water to drain southwards into the Caspian.
This, it was felt, would not only prevent the imminent disappearance of the Caspian Sea, but would also dramatically increase agricultural productivity by making fertile the arid steppes of Kazakhstan, Uzbekistan and all the other -stans that feature on the region's maps.
Further north the Arctic Ocean, without the influx of fresh water from these great rivers, would become progressively more salty; it would be reluctant to freeze during the winter months, and therefore be more navigable to shipping.
Western climatologists were aghast when they heard about the plan. An Arctic Ocean iceless in the wintertime would alter the pattern of the global circulation of the winds, with profound and unpredictable effects upon our climate.
But then a strange thing happened. The shrinking of the Caspian Sea, for no apparent reason, suddenly reversed itself. Since 1977, the level has increased by more than eight feet, although 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 any notions of diverting rivers, and climatologists around the world relaxed.