The long-term global sea surface temperature anomalies: the role of tropics and midlatitudes

The global mean sea surface temperature (SST) anomaly time series in the 60°N-60°S band (GT) has been used to infer the secular climate change. Contributions of the tropical (TT) and extratropical (northern - NT; and southern - ST) sectors to the GT time series are examined. Monthly averaged SST anomaly time series in these selected global zonal bands and in the combined NT and ST band (NST) are constructed. For all bands, the corresponding yearly series for the 1901-2020, 1901-1970, and 1971-2020 periods show significant positive trends, with the largest values during the 1971-2020, except for ST, confirming the global warming acceleration in recent decades. The analysis here suggests that the contributions of the tropical and midlatitudes SST to the GT positive trend depend on the analyzed period and might have influences of the low-frequency variability modes. Concerning the variabilities in the GT time series, at the 0.5-2-year, interannual and interdecadal time scales are, respectively, mostly due to the NST SST anomalies, the TT SST anomalies, and the TT and NST SST anomalies. We believe that our findings might help guide future studies on SST trends and variability.