DECADE-SCALE TRANS-PACIFIC PROPAGATION AND WARMING EFFECTS OF AN EL-NINO ANOMALY

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.