A multiproxy index of the El Nino-Southern Oscillation, AD 1525-1982

An understanding of past variability in the El Nino-Southern Oscillation (ENSO), on interannual, interdecadal, and longer time scales, would be useful in assessing recent observed changes to ENSO and in determining the realism of climate model simulations. Using tree ring, coral, and ice core data, we reconstruct a proxy-based ENSO index between A. D. 1525 and 1982. Unlike most previous studies, which have drawn climate proxies from limited geographic regions, our network is Pacific basin-wide, using ENSO sensitive proxies from the western equatorial Pacific, New Zealand, the central Pacific, and subtropical North America. By considering multiple teleconnection regions, this network provides a more robust proxy ENSO signal. The common signal recorded in the multiproxy network has a high correlation with the Southern Oscillation Index (SOI), Nino 3.4 sea surface temperature (Nino3.4 SST), and a combined ocean-atmosphere ENSO index (CEI). The proportion of instrumental variance explained is 47% for the SOI, 48% for Nino3.4 SST, and 52% for the CEI. The proxy ENSO index also displays skill in reproducing warm and cold extremes of the SOI. The proxy ENSO index over the last 450 years shows considerable amplitude and frequency modulation in the 3-10 year band on multidecadal time scales. There is a relative reduction in the amplitude of high-frequency variability during the sixteenth, early seventeenth, and mid-eighteenth centuries. In contrast, high-frequency ENSO variability has increased over the last 200 years. Variability during the first half of the twentieth century is similar to that evident in the nineteenth century.