Dr. Kimble, geographer and author of Our American Weather, displays a map of the United States, from U.S. News and World Report, that indicates winter temperatures during the past 30-40 years have become milder by 5-8 degrees on the eastern seaboard but gradually decrease going westward, revealing 3-5 degrees colder temperatures in the Pacific northwest. As examples that the weather may be getting warmer, Dr. Kimble shows diagrams of a Canadian glacier's retreat in 1869, 1900, 1933, and 1946. He also cites New York Historical Society photos of the frozen Hudson River, the shifting of traditional boundaries of the corn and wheat belts, the southern birds and animals frequenting northern states in the winter, and the opening of Spitzbergen's arctic port an additional three months of the year. Dr. Kimble says he doesn't know the answer for the change in the weather and suggests sunspot cycles, volcanic dust, ozone content change, but mostly man-generated pollution from factories and motor vehicles.