IN the Mid West of the United States, April 14th, 1935, is remembered as "Black Sunday", because of that day there occurred one of the worst dust storms of the infamous "Dust Bowl" years. The anniversary is a timely reminder that climate can play cruel tricks without any help at all from global warming.
The immediate cause of this tragic period in American history was an anomalous increase in the frequency of westerly winds in the middle latitudes of the northern hemisphere during the six years from 1932 to 1937. Why this should have happened, even in retrospect, nobody quite knows. But happen it did, and in those places whose rainfall his derived mainly from moisture transported from the west - as is the case, for example, in western Europe - the result was an increase in rainfall.
In America, however, most of the Great Plains lay for the duration in the giant rainshadow of the Rockies. Any moisture that the westerly winds might have gathered on their journey across the Pacific was extracted in the form of rainfall as they crossed the mountains, and the winds that swept down into New Mexico, Colorado, Oklahoma, Kansas and the Texas Plains were hot and dry, and brought the worst drought experienced for generations.
A severe drought of this kind occurs regularly about every 20 years in this region. On this occasion, however, its effects were exacerbated by the introduction in the previous decade of mechanised farming methods on a grand scale. During previous droughts, dry winds affecting the native grasses of the area had produced a tough tried up mat that to a large extent protected the underlying soil. But now, once the drought had killed the crops, the soil that had been disturbed by the plough just blew away.
Strong winds brought severe duststorms, rolling like black scourges across the barren plains. People had to wear masks to protect themselves, and drive with their headlights on in day time; dust piled up inside houses; schools and businesses were closed, traffic was stopped, and bereaved families were unable to bury their dead; even the birds, it was said, were too afraid to fly.
When the climate finally returned to normal, much of the affected land was sensibly returned to pasture. In the meantime, however, the natural disaster of the drought had coincided with the economic hardship of the Depression, and thousands of ruined farmers and their families had to abandon their parched holdings and set out along Highway 66 for the green promise of California and the west.