Background
The authors write that "the contribution of anthropogenic climate change to regional climate change is clouded by the presence of naturally occurring variability," a major source of which, on 2-7 year time scales, is the El Niņo-Southern Oscillation (ENSO). With respect to this problem, they state that "extended, multicentury reconstructions of ENSO can help us to assess how unusual 20th century variability in ENSO has been in a longer-term context," and to determine "the realism of climate model simulations."

What was done
Based on tree-ring, coral and ice-core data obtained from the western equatorial Pacific, New Zealand, the central Pacific, and subtropical North America -- which constitute, in their words, "a set of multiproxy indicators from locations that span a broader area of the Pacific basin than has been attempted previously" -- Braganza et al. developed a new annually-resolved Pacific-basin-wide ENSO index for the period AD 1525-1982.

What was learned
The five researchers report that "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." However, they say that "in the context of the entire record, we find no pronounced signal of twentieth century climate change in ENSO variability."

What it means
Contrary to the projections of many climate models that have been made over a period of many years, Braganza et al. were unable to discern any unusual behavior in ENSO activity during the transition from what was the coldest period of the current interglacial to just before what the world's climate alarmists claim was the warmest period of the past two millennia, which finding raises further questions about the validity of the model projections.