Persistent record-high temperatures in the North Pacific in 2014/2015: A climate
hypothesis
Emanuele Di Lorenzo 1 and Nathan Mantua 2
1
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
E-mail: edl@gatech.edu
2
NOAA, Southwest Fisheries Science Center, Santa Cruz, CA, USA
Record-high sea surface temperature anomalies (>3C), also referred as the warm “blob”, developed during
the winter of 2013/2014 in the Gulf of Alaska and spread along the North American coast in the following
winter and spring of 2014/15. These winter anomalies resembled the patterns of the North Pacific Gyre
Oscillation (NPGO) in 2014 and of the Pacific Decadal Oscillation (PDO) in 2015. We suggest that the
generation and interannual persistence of the warm anomalies is driven by large-scale climate
teleconnections between tropics and extra-tropics that are typical of El Niño precursor dynamics. More
specifically, we show that the strong atmospheric ridge that forced the warm “blob” is linked to the
activity of the North Pacific Oscillation (NPO), a well know pattern of atmospheric variability that acts as
stochastic driver for El Niño. Following a strong extra-tropical NPO forcing during winter/spring, El Niño
conditions typically develop in the tropics during the summer. By fall and winter of the following year the
El Niño variability excites atmospheric teleconnections that carry the signal back to the North Pacific and
impact the Aleutian Low (AL). This teleconnection dynamic from extra-tropics (winter year 0) to tropics
to extra-tropics (winter year +1) is a source of significant interannual persistence of North Pacific SSTa
as they evolve from an NPO-like SSTa (e.g. NPGO) to an AL-like SSTa pattern (e.g. PDO). Even though
a strong El Niño did not develop during the fall/winter of 2015, we show that this tropical/extra-tropical
coupling played an important role in the generation and persistence of the 2014/2015 warm “blob”. Given
that previous studies suggest that greenhouse forcing will energize the NPO precursor dynamics, it is
important to establish if the 2014/2015 temperature extreme, and its wide marine ecosystem impact, will
become more frequent under climate change.