Indian Ocean warming modulates Pacific climate change

Abstract

It has been widely believed that the tropical Pacific trade winds weakened in the last century and would further decrease under a warmer climate in the 21st century. Recent high-quality observations, however, suggest that the tropical Pacific winds have actually strengthened in the past two decades. Precise causes of the recent Pacific climate shift are uncertain. Here we explore how the enhanced tropical Indian Ocean warming in recent decades favors stronger trade winds in the western Pacific via the atmosphere and hence is likely to have contributed to the La Niña-like state (with enhanced east-west Walker circulation) through the Pacific oceanatmosphere interactions. Further analysis, based on 163 climate model simulations with centennial historical and projected external radiative forcing, suggests that the Indian Ocean warming relative to the Pacific's could play an important role in modulating the Pacific climate changes in the 20th and 21st centuries.

Recent Walker circulation strengthening and Pacific cooling amplified by Atlantic warming

“…The ensemble mean results of this experiment do not show a considerable trans-basin SLP see-saw and no significant wind stress anomalies in the equatorial Pacific (Supplementary Figs 3c, 5 and Table 2), in contrast to recent studies 5,13 that have proposed a more active role of Indian Ocean SST trends in causing Pacific trade wind changes.…”

Drying of Indian subcontinent by rapid Indian Ocean warming and a weakening land-sea thermal gradient

“…Research based on climate proxy records and models point out that the climate signals forced by warm SST anomalies over the tropical Indian and western Pacific oceans synergistically contribute to widespread drying over South Asia and mid-latitudes, an ideal scenario for a large-scale drought 63,64 . In addition, a recent study points out that the Indian Ocean warming may also be playing an important role in modulating the Pacific climate change in recent decades, by favouring stronger trade winds in the Pacific, thereby contributing to the recent global warming hiatus 65 . Hence, the critical role of the warm Indian Ocean deserves special attention not only for its decisive effect on the food security of a large fraction of the world's population, but also due to its disproportionately large role as a partner to the warm pool Pacific in inducing a drought, as well as its potential role in the global warming pause.…”

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

“…Modeling studies suggest that warming of the tropical Indian and Atlantic Oceans enhances surface easterly trade winds and thus contributes to the intensified SLR (e.g., Luo et al 2012;Han et al 2014a;Hamlington et al 2014;England et al 2014;McGregor et al 2014); however, a large portion of this rapid SLR-together with weak falls in the eastern basin-is part of the basin-scale sea level pattern associated with the Pacific Decadal Oscillation (PDO) or decadal variability of ENSO (Bromirski et al 2011;Merrifield et al 2012;Meyssignac et al 2012;Zhang and Church 2012;Hamlington et al 2013Hamlington et al , 2014Moon et al 2013;Han et al 2014a; Palanisamy et al 2015). The PDO is defined as the leading empirical orthogonal function (EOF) of sea surface temperature (SST) anomaly over the North Pacific ([20°N), and the leading principal component (PC1) is referred to as the PDO index (e.g., Mantua et al 1997;Minobe 1997;Zhang et al 1997;Garreaud and Battisti 1999; see review papers by Alexander 2010;Liu 2012).…”