El Nino events in the Pacific Ocean can have significant local effects
lasting up to two years. For example the 1982-83 El Nino caused incre
ases in the sea-surface height and temperature at the coasts of Ecuado
r and Peru(1), with important consequences for fish populations(2,3) a
nd local rainfall(4). But it has been believed that the long-range eff
ects of El Nino events are restricted to changes transmitted through t
he atmosphere, for example causing precipitation anomalies over the Sa
hel(5). Here we present evidence from modelling and observations that
planetary-scale oceanic waves, generated by reflection of equatorial s
hallow-water waves from the American coasts during the 1982-83 El Nino
, have crossed the North Pacific and a decade later caused northward r
e-routing of the Kuroshio Extension-a strong current that normally adv
ects large amounts of heat from the southern coast of Japan eastwards
into the mid-latitude Pacific. This has led to significant increases i
n sea surface temperature at high latitudes in the northwestern Pacifi
c, of the same amplitude and with the same spatial extent as those see
n in the tropics during important El Nino events. These changes may ha
ve influenced weather patterns over the North American continent durin
g the past decade, and demonstrate that the oceanic effects of El Nino
events can be extremely long-lived.