Now warming is the specter, with its melting glaciers, inundated cities, and the Gulf Stream reversing course. But I doubt if the enviros can keep on fomenting the scare much longer. It has been based on little more than extrapolated temperatures and spurious charts. What are the facts? Surface temperature measurements show a global warming period from about 1910 to 1940, followed by a cooling period until 1975. Since then we have experienced a slight warming trend. These three periods add up to a surface-temperature increase of perhaps one-degree Fahrenheit for the entire 20th century.