POSSIBLE FORCING OF GLOBAL TEMPERATURE BY THE OCEANIC TIDES

An approximately decadal periodicity in surface air temperature is dis cernable in global observations from A.D. 1855 to 1900 and since A.D. 1945, but with a periodicity of only about 6 years during the interven ing period, Changes in solar irradiance related to the sunspot cycle h ave been proposed to account for the former, but cannot account for th e latter, To explain both by a single mechanism, we propose that extre me oceanic tides may produce changes in sea surface temperature at rep eat periods, which alternate between approximately one-third and one-h alf of the lunar nodal cycle of 18.6 years, These alternations, recurr ing at nearly 90-year intervals, reflect varying slight degrees of mis alignment and departures from the closest approach of the Earth with t he Moon and Sun at times of extreme tide raising forces, Strong forcin g, consistent with observed temperature periodicities, occurred at 9-y ear intervals close to perihelion (solar perigee) for several decades centered on A.D. 1881 and 1974, but at 6-year intervals for several de cades centered on A.D. 1923. As a physical explanation for tidal forci ng of temperature we propose that the dissipation of extreme tides inc reases vertical mixing of sea water, thereby causing episodic cooling near the sea surface, If this mechanism correctly explains near-decada l temperature periodicities, it may also apply to variability in tempe rature and climate on other times-scales, even millennial and longer.