Interdecadal changes in the behaviour of ENSO

Trenberth & Hoar (1) have compared the 1990-1995 El Niño against others during 1882-1997, and shown how unusual it was, notably as regards duration. As a result some areas experienced prolonged drought conditions. In fact, ENSO events during the whole of the period since 1976 are remarkable for their prolongation, and it is shown statistically that such enduring times of negative SOI (and overall higher SST in the equatorial Pacific) are not likely to be due simply to natural variability. Also, the 3 most intense El Niño events of the last century may have happened during the last 25 years (1972, '82, and '97). The authors suspect that it is associated with global warming, which could imply increasingly serious droughts in the future in some regions.

Also, El Niño events appear to have been more intense in the 20^th century compared with 1400-1900 (2).

1. Trenberth, K.E. and T.J. Hoar, 1997: El Niño and climate change. Geophys. Res. Letters 24, 3057-60.
2. Mann, M.E., R.S. Bradley and M.K. Hughes 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature, 392, 779-803.