PNNL

Abstract

Using multiple observational and modeling datasets, we document a strengthening relationship between boreal winter sea surface temperature anomalies (SSTA) in the western North Pacific (WNP) and the development of the El Nino-Southern Oscillation (ENSO) one year later. The increased WNP-ENSO association emerged in the mid 20th century and has grown through the present, reaching correlation coefficients as high as ~0.70 in recent decades. Fully coupled climate experiments with the Community Earth System Model (CESM) replicate the WNP-ENSO association and indicate that greenhouse gases (GHG) are largely responsible for the observed increase. We speculate that shifts in the location and amplitudes of positive SST trends in the subtropical-tropical western Pacific impacts the low-level circulation so that WNP variability is increasingly influencing the development of ENSO one year later. A strengthened GHG-driven relationship between the WNP and ENSO provides an example of how anthropogenic climate change can potentially improve the skill of intraseasonal-to-interannual climate prediction.