Co-effect of Tropical Pacific Decadal Variability and Cold Ocean-Warm Land Pattern on Global Warming Slowdown and Acceleration

Abstract:

Internally generated decadal variability modulates the rate of global warming under anthropogenic radiative forcing. While previous studies have shown that tropical Pacific decadal variability (TPDV) plays a crucial role in generating decadal-long periods of slowdown and acceleration of global warming, substantial internal temperature variations in the Northern Hemispheric extratropics are independent of TPDV, particularly in boreal cold season. Here we find that, in boreal cold season, the mean extratropical temperature variation in the Northern Hemisphere is well tracked by the so-called cold ocean–warm land (COWL) pattern, the decadal variability of which is important for modulating global warming rate. After the mid-1980s, TPDV and COWL variability vary in phase by chance to strengthen internal decadal variations in global mean surface temperature, contributing to the early 2000s slowdown and early 2010s acceleration. Specifically, this synchronized modulation notably occurs in boreal cold season which results from the seasonality of TPDV and COWL. Further analyses based on climate model simulations suggest that in a warming future, the co-variability of TPDV and COWL is still important for modulating global warming rate while their respective spatial pattern may change. Although TPDV shows some predictabilities, we highlight that COWL is largely induced by atmospheric internal variability, which limits the predictability of global warming slowdown and acceleration.