National Geographic : 1976 Nov
The ice wall cometh to a forest in south-central Alaska (left), where Meares Glacier nudges toward Prince William Sound at 100 feet a year. At triple that pace, other rivers of ice flow down Mount McKinley's vegetation-mantled slopes, red in this false-color Landsat portrait (below). Miniatures of the great ice sheets that advance about every 100,000 years, glaciers serve as thermometers for lesser temperature changes. Most scien tists agree that today's ice movement may reflect a worldwide cooling trend, but their explanations vary widely. it will go next-may be the biggest question about the earth yet to be answered," marine geologist John Imbrie told me at Brown Uni versity in Rhode Island. Dr. Imbrie helps lead a major U. S. Government-funded effort, nicknamed CLIMAP (for Climate: Long-Range Investigation, Mapping, and Prediction), to chart weather patterns of the past in hope of learning what may happen in the future. "In the 1970's, really for the first time, we have the tools-satellites, big computers, and so on-as well as the data to attack that ques tion. To me, this is the most exciting and criti cal challenge facing science today." And just what is going on with the climate? What changes are taking place around us? "From 1880 to about 1940 the world particularly the Northern Hemisphere-went through a period of significant warming," I heard from tall, quiet-spoken Dr. J. Murray Mitchell, Jr., of the National Oceanic and Atmospheric Administration (NOAA); he is one of this nation's most respected clima tologists (next page). He went on: "But since about 1940, there has been a distinct drop in average global temperature. It's fallen about half a degree Fahrenheit-even more in high latitudes of the Northern Hemisphere." England's annual growing season shrank by nine or ten days between 1950 and 1966, Hubert Lamb has noted. In the northern tier of the U. S. Midwest, summer frosts again oc casionally damage crops. Sea ice has returned to Iceland's coasts after more than forty years of virtual absence. During the last 20 to 30 years, world temperature has fallen, irregularly atfirst but more sharply over the last decade. U. S. NATIONAL SCIENCE BOARD, 1974 Glaciers in Alaska and Scandinavia have slowed their recession; some in Switzerland have begun advancing again. Yet, oddly, in the eastern United States, western Soviet Union, and much of Europe the winters of 1973 through 1975 were the warmest in decades. And recent studies have hinted that the Southern Hemisphere may be What's Happening to Our Climate?