Future Extreme Sea Level Variability in the Tropical Pacific

Wednesday, 17 December 2014
Matthew J Widlansky1, Axel Timmermann2, Malte F Stuecker3, Shayne McGregor4, Wenju Cai5 and Yoshimitsu Chikamoto1, (1)University of Hawaii at Manoa, Honolulu, HI, United States, (2)IPRC-SOEST, Honolulu, HI, United States, (3)University of Hawai''i at Mano, Honolulu, HI, United States, (4)University of New South Wales, Sydney, Australia, (5)CSIRO, Aspendale, Australia
During strong El Niño events, sea level drops around tropical western Pacific islands by up to 20–30 cm. Such extreme events (referred to in Samoa as ‘taimasa’) expose shallow reefs, thereby damaging associated coastal ecosystems and contributing to the formation of ‘flat topped coral heads’ often referred to as microatolls. We show that during the termination of strong El Niño events, a southward movement of weak trade winds prolongs extreme low sea levels in the southwestern Pacific. Whereas future sea levels are projected to gradually rise, recent modeling evidence suggests that the frequency of strong El Niño events (which alter local trade winds and sea level) is very likely to increase with greenhouse warming. Such changes could exacerbate El Niño-related sea level drops, especially in the tropical southwestern Pacific. Using present-generation coupled climate models forced with increasing greenhouse-gas concentrations, we assess how the interplay between global mean sea level rise, on one hand, and more frequent interannual sea level drops, on the other, will affect future coastal sea levels in the tropical Pacific.