Central tropical Pacific corals constrain anthropogenic influence on recent ENSO extremes

Pamela R Grothe1, Kim M Cobb1, R. Lawrence Edwards2, Hai Cheng3, Daniel Deocampo4, John Richard Southon5, Guaciara Santos6, Yanbin Lu7, Giovanni Liguori8 and Antonietta Capotondi9, (1)Georgia Institute of Technology Main Campus, Earth and Atmospheric Sciences, Atlanta, GA, United States, (2)University of Minnesota, Minneapolis, MN, United States, (3)Xi'an Jiaotong University, Institute of Global Environmental Change, Xian, China, (4)Georgia State University, Department of Geosciences, Atlanta, GA, United States, (5)Univ California, Irvine, CA, United States, (6)University of California Irvine, Irvine, CA, United States, (7)University of Minnesota, Department of Earth Sciences, Minneapolis, MN, United States, (8)Georgia Institute of Technology, School of Earth & Atmospheric Sciences, Atlanta, GA, United States, (9)NOAA /ESRL, Physical Sciences Division, Boulder, CO, United States
Abstract:
The recent spate of strong and very strong El Niño events (1982/83, 1997/98, 2015/16) raises the specter that the El Niño Southern Oscillation is intensifying in response to anthropogenic greenhouse warming. CMIP5 models generally suggest that extreme El Niño and La Niña events will increase owing to changes in the mean state of the tropical Pacific climate system (e.g. Cai et al., 2015). However, potential anthropogenic trends in ENSO properties are difficult to detect in the short record of instrumental climate data from the tropical Pacific. Here we extend the record using paleoclimate data to quantify the differences in natural variations in ENSO behavior to the observations from the industrial era. Monthly-resolved coral d18O records from the heart of the ENSO region, in the central tropical Pacific, track changes in sea surface temperature with high fidelity and have been used to quantify ENSO variability over the last 7,000 years (Cobb et al., 2013). Cobb et al. (2013) detected a statistically significant increase in ENSO variability during the late 20th century, implying a role for greenhouse gases in fueling larger ENSO extremes. However, ENSO variability has been relatively subdued in the 21st century, warranting a reanalysis of coral datasets that extend through the 2015/2016 El Niño event. Using an expanded dataset of fossil coral d18O records from across the Line Islands, we quantify the differences in ENSO variability between the last 100 years and the last 7,000 years. ENSO variability during the late 20th and early 21st century is higher than most periods in the past, but the significance of this difference is somewhat dependent upon the window length considered for the analyses, given the high variability of past ENSO activity. Nonetheless, our data provide qualitative, empirical support for model projections documenting an increase in extreme El Niño events under continued greenhouse forcing (Cai et al., 2015).
Back to: El Niño–Southern Oscillation (ENSO) Diversity in a Changing Climate II