More extreme swings of the South Pacific convergence zone due to greenhouse warming.
The South Pacific convergence zone (SPCZ) is the Southern Hemisphere's most expansive and persistent rain band, extending from the equatorial western Pacific Ocean southeastward towards French Polynesia. Owing to its strong rainfall gradient, a small displacement in the position of the SPCZ causes drastic changes to hydroclimatic conditions and the frequency of extreme weather events--such as droughts, floods and tropical cyclones--experienced by vulnerable island countries in the region. The SPCZ position varies from its climatological mean location with the El Niño/Southern Oscillation (ENSO), moving a few degrees northward during moderate El Niño events and southward during La Niña events. During strong El Niño events, however, the SPCZ undergoes an extreme swing--by up to ten degrees of latitude toward the Equator--and collapses to a more zonally oriented structure with commensurately severe weather impacts. Understanding changes in the characteristics of the SPCZ in a changing climate is therefore of broad scientific and socioeconomic interest. Here we present climate modelling evidence for a near doubling in the occurrences of zonal SPCZ events between the periods 1891-1990 and 1991-2090 in response to greenhouse warming, even in the absence of a consensus on how ENSO will change. We estimate the increase in zonal SPCZ events from an aggregation of the climate models in the Coupled Model Intercomparison Project phases 3 and 5 (CMIP3 and CMIP5) multi-model database that are able to simulate such events. The change is caused by a projected enhanced equatorial warming in the Pacific and may lead to more frequent occurrences of extreme events across the Pacific island nations most affected by zonal SPCZ events.
CSIRO Marine and Atmospheric Research, Aspendale, Victoria 3195, Australia. wenju.cai@csiro.au
Wenju
W
Cai
Matthieu
M
Lengaigne
Simon
S
Borlace
Matthew
M
Collins
Tim
T
Cowan
Michael J
MJ
McPhaden
Axel
A
Timmermann
Scott
S
Power
Josephine
J
Brown
Christophe
C
Menkes
Arona
A
Ngari
Emmanuel M
EM
Vincent
Matthew J
MJ
Widlansky
D016208:Databases, Factual; D059000:El Nino-Southern Oscillation / Q000266:history; D057232:Global Warming / Q000191:economics / Q000266:history / Q000706:statistics & numerical data*; D017752:Greenhouse Effect / Q000191:economics / Q000266:history / Q000706:statistics & numerical data*; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D008962:Models, Theoretical; D010140:Pacific Ocean; D011891:Rain; D012959:Socioeconomic Factors