Cerveny, R.S. and Shaffer, J.A. 2001. The moon and El Niņo. Geophysical Research Letters 28: 25-28.
A lack of understanding of the physical forcing mechanism(s) driving ENSO is perhaps one reason why climate alarmists are quick to claim that CO2-induced global warming will increase the frequency and magnitude of ENSO events. Such claims, however, as we have reported previously, are not supported by the observational record (see our Subject Index headings ENSO, ENSO - Summary). We now report the results of an intriguing study that hypothesizes a natural forcing of ENSO by lunar tidal forces.
What was done
The authors examined the possibility that lunar tidal forces act as an external forcing mechanism in regulating sea surface temperatures tied to ENSO events.
What was learned
A statistically significant correlation was found between maximum lunar declination (MLD) and both equatorial Pacific sea surface temperatures and South Pacific atmospheric pressure (the Southern Oscillation Index) over the period 1854 to 1999. High MLDs were associated with La Niņa conditions, while low MLDs were associated with El Niņo conditions. Under high MLD, circulation in the Pacific gyre is enhanced by tidal forces, inducing cold-water advection into the equatorial region that is characteristic of La Niņa conditions. Under low MLD, on the other hand, tidal forcing is weakened, cold water advection is reduced, and warmer sea surface conditions characteristic of El Niņo prevail.
What it means
The importance of lunar forcing on climate appears to be gaining momentum in climate change discussions (see Lunar Tides and Climate Change). However, the authors readily acknowledge that while ENSO events appear to be "substantially associated with MLD," they correctly note that "other factors must still be considered and investigated." Projecting the relationships they developed into the future, the authors find that MLD is currently increasing and will continue to do so over the next several years, indicating "a greater potential for the occurrence of colder SSTs in the equatorial Pacific, or non-El Niņo (either La Niņa or neutral) conditions."