Some of the largest trends in 20th century surface air temperature have been observed in the higher latitudes of the Northern Hemisphere. These areas include both large portions of Russia and parts of Canada. However, recent speculation (e.g. Singer 2001) has questioned whether these trends are indicative of large-scale warming, or due to other, more localized causes. Here we examine evidence of temperature changes in the Northern Hemisphere that includes examining the contribution of these areas to the trends in globally averaged temperature, and documenting the seasonal changes using daily maximum and minimum temperature data, and supporting proxy evidence such as tree ring data and temperatures developed from boreholes.