Experts say the polar vor­tex is caused by glob­al warm­ing and dis­ap­pear­ing ice, but forty years ago they said it was caused by glob­al cool­ing and expand­ing ice.

Sci­en­tists have found oth­er indi­ca­tions of glob­al cool­ing. For one thing there has been a notice­able expan­sion of the great belt of dry, high-alti­tude polar winds —the so-called cir­cum­po­lar vor­tex—that sweep from west to east around the top and bot­tom of the world. Indeed it is the widen­ing of this cap of cold air that is the imme­di­ate cause of Africa’s drought. By block­ing mois­ture-bear­ing equa­to­r­i­al winds and pre­vent­ing them from bring­ing rain­fall to the parched sub-Sahara region, as well as oth­er drought-rid­den areas stretch­ing all the way from Cen­tral Amer­i­ca to the Mid­dle East and India, the polar winds have in effect caused the Sahara and oth­er deserts to reach far­ther to the south. Para­dox­i­cal­ly, the same vor­tex has cre­at­ed quite dif­fer­ent weath­er quirks in the U.S. and oth­er tem­per­ate zones. As the winds swirl around the globe, their souther­ly por­tions undu­late like the bot­tom of a skirt. Cold air is pulled down across the West­ern U.S. and warm air is swept up to the North­east. The col­li­sion of air mass­es of wide­ly dif­fer­ing tem­per­a­tures and humid­i­ty can cre­ate vio­lent storms—the Midwest’s recent rash of dis­as­trous tor­na­does, for example.

TIME Mag­a­zine Archive Arti­cle — Anoth­er Ice Age? — Jun. 24, 1974