Influence of atmospheric oscillations on northern hemispheric temperature

Global warming has become a major scientific and political issue during the past 2 decades. Evidences show that the change of surface temperature is not uniform. The temperature is increased dramatically over northern continents in middle and high latitudes, but dropped obviously in northern Atlantic and northern Pacific. So the variation of temperature demonstrate some inherent structure. Atmospheric circulation is the most dominant factor controlling the surface climate changes. Atmospheric oscillations play an important role in the general atmospheric circulation, and affect regional or planetary scale climatic anomaly. Variance contribution of three atmospheric oscillations, say NAO (North Atlantic Oscillation), NPO (North Pacific Oscillation) and SO(Southern Oscillation), to north hemispheric temperature is investigated. Multivariate linear regression analysis show that the contribution is much higher in the tropic region, middle and high latitude continent and north western Pacific. Three atmospheric oscillations account for above 30% temperature variance over continent of north 40°N, and most part of the tropic in winter. During the past century, the contribution of atmospheric oscillations to northern hemispheric surface air temperature is also significant. From 1873 to 1993, temperature variance of the north hemisphere explained by the atmospheric oscillations is about 31 8%, 2 6% and 12 8% for winter, summer and annual respectively. During the last 2 decades the NAO index is increasing impressing, and the El Nino events occur with a much high frequency. Most part of the warming trend after the mid 1970s may be related to the decadal changes of NAO, NPO and SO.