Large quantities of ice or snow take a relatively long time to melt. Wordsworth, for example, noticed this in the mountains of the Lake District, where he saw little pockets of snow or hail that had survived well into early summer: It was a cove, a huge recess, That keeps till June, December's snow.
And Patrick Kavanagh evokes the same image with more subtlety:
My hills hoard the bright shillings of March While the sun searches in every pocket.
In the 1970s this relative longevity was thought of as a possible solution to drought in areas of the world where fresh water is scarce. It was suggested that large icebergs might be towed southwards from the polar regions to be anchored, for example, off Saudi Arabia, and the water from them harvested during the dry season. Estimates at the time were that only 50 per cent of an iceberg would be lost en route by melting.
There is no shortage of icebergs for such purposes. Every year up to 16,000 of them are formed in the northern hemisphere. As snow accumulates on the Greenland icecap, its weight pushes the ice near the coast further and further down into the sea; the edges break off - or calve - to form the icebergs.
They vary greatly in size: small ones up to 20 or 30 feet in diameter are often called "growlers" by seamen, but great cones of ice that measure hundreds of feet in diameter are common, and there have been some giants half-a-mile or more across.
Most of the icebergs drift southwards with the Labrador Current along the western part of the North Atlantic, often causing problems in the shipping-lanes - as happened, for example, in the case of the Titanic in April, 1912.
But there were serious snags to the artificial transportation of icebergs to the lower latitudes. First, there was the physical problem of towing a giant lump of ice: an iceberg of suitable size would be too heavy to be handled by even the most powerful of tugs available. Moreover, the process of attaching a cable - assuming one knew how to do it - would be a hazardous one, since icebergs have a nasty habit of suddenly toppling over when their centre of gravity shifts position as great chunks of ice break off.
And then there would be problems at the destination. You cannot berth a giant iceberg neatly by the quayside, since nine-tenths of it is beneath the surface; processing the ice some distance from the shore to obtain the required water would pose a major challenge.