An estimate of average annual temperature variations for North America, 1602 to 1961

Annual surface temperature variations, 1602 to 1961, averaged over 77 United States and southwestern Canadian stations, are reconstructed from 65 aridsite tree-ring chronologies of western North America. Annual sea-level pressure reconstructions averaged over the North Pacific sector including North America and eastern Asia are inversely related to the temperature variations. Both the instrumental and reconstructed North American temperature averages are well correlated with Northern Hemisphere average temperatures during the early 20th-century warming but the correlation diminishes after the mid-1940s. The 1918 to 1947 interval is reconstructed to have been the warmest and 1877 to 1906 the coolest. The correlations between the temperature record and other high resolution temperature series from the Northern Hemisphere are generally insignificant. However, significant correlations are noted for certain 30-yr time periods. North American temperatures appear to have been out of phase with temperatures in Europe during the late 18th and early 19th centuries. Significant variations in the 30-yr mean temperatures are noted in several of the North American series. The warming early in the 20th century is the most marked followed by warming from 1717 to 1723 and from 1850 to 1866. Significant cooling occurs from 1810 to 1821 and from 1659 to 1669.