Recent Observed Interdecadal Climate Changes in the Northern Hemisphere

The largest increases in surface temperatures over the Northern Hemisphere in the decade prior to 1988 were in Alaska, while substantial decreases occurred in the North Pacific Ocean. This illustrates the considerable geographic spatial structure to interdecadal temperature variations associated with changes in the atmospheric circulation. In particular, from 1977 to 1988, there was a deeper and eastward-shifted Aleutian low-pressure system in the winter half year, which advected warmer and moister air into Alaska and colder air over the North Pacific. Associated changes in surface-wind stress and wind-stress curl altered the North Pacific Ocean currents, as revealed by the Sverdrup transport. The North Pacific changes appear to be linked through teleconnections to tropical atmosphere–ocean interactions and the frequency of El Niño versus La Niña events. Consequently, the question of why it was so warm in Alaska becomes changed to one of why there were three tropical Pacific Warm Events, but no Cold Events, from 1977 to 1988, and whether changes in El Niño frequency will be altered during climate change. At the very least, these linkages and the resulting strongly regional structure of surface-temperature variations complicate any search for a greenhouse effect and global warming.