Modes of SST variability and the fluctuation of global mean temperature

Annually averaged global mean land air temperature and sea surface temperature (SST) combined, and global mean SST alone share similar fluctuations. We examine contributions by modes of SST variability in the global mean SST based on a new version (version 3) of global sea-ice and SST (GISST3). Besides a trend mode, the dominant modes are El Nino-Southern Oscillation (ENSO), interhemispheric, oscillation, and North Pacific oscillation. Statistics over the period of 1880-1997 show that excluding a warming trend the fluctuation on interannual (IA) and decadal-interdecadal (DID) time scales is dominated by IA ENSO and DID ENSO-like variability. However, the contribution by IA ENSO cycles experiences significant fluctuations, and there appears to be strong modulations by ENSO-like variability on DID or longer time scales: during several decade-long periods, when DID ENSO-like variability raises the temperature in the equatorial eastern Pacific, the contribution by IA ENSO cycles weakens to an insignificant level. The latest example of such modulation is the period since about 1980; despite the exceptional strength of El Nino events, the contribution by IA ENSO cycles weakens, suggesting that the exceptional strength is a consequence of superposition of IA El Nino events, a warming phase of DID ENSO-like variability, and possibly an ENSO-like warming trend.