It is almost a century and a half since the Walrus and the Carpenter took their celebrated walk along the beach. There, you may recall:
They wept like anything to see
Such quantities of sand;
"If this were only cleared away,
They said, "it would be grand".
If the pair were to retrace their steps today, they might be less depressed. The chances are the beach would be smaller than it used to be and significantly less sand would be in evidence.
The riddle of the shrinking beaches was identified 30 years ago when a muster of geographers, assembled for a meeting of the International Geographical Union. Virtually all of them could quote several examples of sandy beaches that were being gradually eroded by the sea, but hardly any knew of a beach that had got bigger.
They decided to investigate. Ancient maps and charts, old photographs and written descriptions of what various coastlines had looked like in days gone by were closely examined to build up a picture of the past. This was compared with air and ground photographs of those same beaches as they now are.
After several years of hard work, the results confirmed their intuitive impression - the world's beaches are slowly disappearing.
The figures showed that more than 70 per cent of sandy coastlines around the world had shrunk at a rate of 10 cm or more a year during the last 100 years; fewer than 10 per cent of the world's beaches had grown, with the remaining 20 per cent having stayed more or less the same.
One reason for the retreat of the sandy beaches was relatively clear. Mean sea level had risen by about 10 cm during the period in question, so it was scarcely surprising that beaches should suffer some erosion.
In former times when there was a rise in sea level, beaches would move bodily inland; now sea walls, roads and houses line coasts, so when the sea rises and washes away the old beach, the sand cannot push inland. There is nowhere for the beach to grow on the land side.
Lewis Carroll's beach-walkers considered various impractical methods of disposing of the irksome sand:
"If seven maids with seven mops,
Swept it for half a year,
Do you suppose," the Walrus said,
That they could get it clear?"
"I doubt it," said the Carpenter
And shed a bitter tear.
But now it seems as if the problem may be solved by other means.