Decadal Oscillations of the Mean Temperature of the Northern Hemisphere during Modern Global Warming

The mean temperatures of surface air, lower troposphere, and upper ocean layer from 0 to 100 m in the Northern Hemisphere are considered. All these time series are similar to each other: they consist of two components, a warming trend and approximately decadal oscillations superimposed on it. A hypothesis is put forward that this quasi-decadal temperature variability is associated with the El Niño–Southern Oscillation. After the trends are removed from the studied time series, their autocorrelation functions demonstrate an exponential decrease and subsequent oscillations near zero with shifts of ~5 years or more, which theoretically allows us to predict their changes with a lead time of 1–4 years. Analysis of the Historical experiment results with 58 CMIP6 models confirmed the conclusions and also showed that large volcanic eruptions have a significant effect on the quasi-decadal variability of the mean surface air temperature in the Northern Hemisphere. Results from the piControl experiment using 50 CMIP6 models demonstrated the ability to predict changes in the mean temperature of the Northern Hemisphere for several years ahead based on the natural interannual climate variability, the main component of which is the El Niño–Southern Oscillation.