Slide 20: Is oceanic circulation changing?
The El Niño Southern Oscillation is a current system that is the primary global mode of variation on the 2 to 7 year time interval, typified by a change in SST anomaly. (IPCC, 2001).
ENSO is associated with extreme climatic events .
Multiproxy reconstruction of ENSO suggests recent extremes are outside the norms of historic conditions.
The 1990s in particular show trends outside the norms of previous decades, including reduced variability (more El Niño events with reduced occurrence of the corollary cool La Niña) (Goddard and Graham, 1997).
Similar statistical anomalies have been observed in both the North Atlantic Oscillation and the North Pacific Oscillation.
These anomalies may be part of a larger variation, or may be part of the natural cycle - it is too early to determine for certain at this stage.
Goddard, L. and N.E. Graham, 1997: El Nino in the 1990s. J. Geophys. Res., 102, 10423-10436.
IPCC, 2001: The third assessment report of the International Panel on Climate Change