The North Atlantic Oscillation: Past, present, and future

The climate of the Atlantic sector exhibits considerable variability on a w ide range of time scales. A substantial portion is associated with the Nort h Atlantic Oscillation (NAO), a hemispheric meridional oscillation in atmos pheric mass with centers of action near Iceland and over the subtropical At lantic. NAO-related impacts on winter climate extend from Florida to Greenl and and from northwestern Africa over Europe far into northern Asia. Over t he last 3 decades, the phase of the NAO has been shifting from mostly negat ive to mostly positive index values. Much remains to be learned about the m echanisms that produce such low frequency changes in the North Atlantic cli mate, but it seems increasingly likely that human activities are playing a significant role.