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 increases in the sea-surface height and temperature at the coasts of Ecuador and Peru(1), with important consequences for fish populations(2,3) and local rainfall(4). But it has been believed that the long-range effects of El Nino events are restricted to changes transmitted through the atmosphere, for example causing precipitation anomalies over the Sahel(5). Here we present evidence from modelling and observations that planetary-scale oceanic waves, generated by reflection of equatorial shallow-water waves from the American coasts during the 1982-83 El Nino, have crossed the North Pacific and a decade later caused northward re-routing of the Kuroshio Extension-a strong current that normally advects large amounts of heat from the southern coast of Japan eastwards into the mid-latitude Pacific. This has led to significant increases in sea surface temperature at high latitudes in the northwestern Pacific, of the same amplitude and with the same spatial extent as those seen in the tropics during important El Nino events. These changes may have influenced weather patterns over the North American continent during the past decade, and demonstrate that the oceanic effects of El Nino events can be extremely long-lived.