Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing

Abstract

Since the mid-nineteenth century the Earth's surface has warmed, and models indicate that human activities have caused part of the warming by altering the radiative balance of the atmosphere. Simple theories suggest that global warming will reduce the strength of the mean tropical atmospheric circulation. An important aspect of this tropical circulation is a large-scale zonal (east-west) overturning of air across the equatorial Pacific Ocean--driven by convection to the west and subsidence to the east--known as the Walker circulation. Here we explore changes in tropical Pacific circulation since the mid-nineteenth century using observations and a suite of global climate model experiments. Observed Indo-Pacific sea level pressure reveals a weakening of the Walker circulation. The size of this trend is consistent with theoretical predictions, is accurately reproduced by climate model simulations and, within the climate models, is largely due to anthropogenic forcing. The climate model indicates that the weakened surface winds have altered the thermal structure and circulation of the tropical Pacific Ocean. These results support model projections of further weakening of tropical atmospheric circulation during the twenty-first century.

A review of observed and projected changes in climate for the islands in the Caribbean

“…However, the global climate models used in this study show a varying degree of performances when tested for their ability to capture ENSO variations and disagree significantly on its future behavior (AchutaRao and Sperber, 2006). Studies that suggest a perpetual El Niño-like state for the Pacific in the future (Vecchi et al, 2006;Vecchi and Soden, 2007;DiNezio et al, 2009) are consistent with a summer drying in the Caribbean. However, the nature of ENSO and NAO variations in response to elevated levels of GHGs remains highly uncertain and is a limitation to examining future changes in interannual variability of Caribbean climate.…”

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

“…The current study discusses the role of Indian Ocean warming in weakening of the monsoon, but does not rule out the possibility that similar impacts may also arise due to SST changes in the tropical Pacific and the Atlantic 9,54,[57][58][59][60][61] . Recent studies show that the Pacific warming trend during the past century is not prominent as compared with the Indian Ocean warming while the tropical and extratropical Atlantic show strong warming trends 28 .…”

“…A few recent studies have also pointed out the increasing frequency of extreme rainfall events over the South Asian monsoon domain, due to a warming climate 3 . However, quite a few other studies indicate that the monsoon rainfall [4][5][6] and the Hadley and Walker circulations [7][8][9] are weakening over the South Asian domain during the past half century (since 1950s). Some of these studies suggest that, though the extreme rainfall events have increased over some regions 3 , the frequency of moderate-to-heavy rainfall events has decreased over the subcontinent 8 .…”

The Capricorn Eddy: a prominent driver of the ecology and future of the southern Great Barrier Reef

“…There is a growing consensus among oceanographers and climate model simulators that the Walker Circulation, of which the equatorial trade winds in the Pacific are the surface manifestation, will weaken as atmospheric concentrations of CO 2 continue to increase (Vecchi et al 2006). Accordingly, the associated trans-Pacific tilt of the near-equatorial oceanic thermocline (Bjerknes 1966) can be expected to lessen, and the coupled Pacific oceanatmosphere system to become more chronically ''El Niño''-like (Quinn 1974;Wyrtki 1975) in its underlying mean background state.…”