El Nino has been one of the most heavily publicized topics in environmental science in recent years. A large and confusing array of terms has been developed to refer to essentially the same phenomenon, which the scientific community has addressed through an international and interdisciplinary approach.
The evolution of scientific concepts regarding El Nino may be traced from a purely phenomenological awareness at the beginning of the century through a growing realization of its global connections, understanding of the role of air-sea interactions, and finally analysis with ocean atmosphere models.
The normal patterns of temperature and circulation in the Pacific involve warm water and a deep thermocline in the west; cold water, shallow thermo- cline, and upwelling in the east; and strong trade winds maintaining high sea levels in the west.
Image Source: photojournal.jpl.nasa.gov
ADVERTISEMENTS:
In vertical cross section, the Pacific may be likened to an asymmetrically heated basin with rising air and precipitation in the west, and the reverse in the east. What happens when this system is perturbed? Anomalies in ocean forcing by the winds could initiate Kelvin and Rossby waves.
The former, travelling eastward along the equatorial wave guide, deepen the thermocline in the eastern Pacific, interrupting normal upwelling, and producing the anomalously warm sea-surface temperatures characteristic of El Nino; the latter seem to propagate to higher latitudes, with implications for temperate zone climate.
The impacts of El Nino on biological systems such as fisheries have attracted some attention. El Nino was originally described purely as a local biological anomaly. There is no strong evidence that El Nino alone had been responsible for major long-term changes in the highly productive Humboldt Current ecosystem in recent decades.
ADVERTISEMENTS:
Rather, a complex set of interactions among physical, biological, and social/economic factors may be operating. Between the 1960’s and the 1970’s, the fisheries saw a major collapse in anchoveta landings, and a shift from an anchoveta dominated system to a mixed system of sardines and other pelagic fishes.
El Nino has clearly demonstrable economic effects on the fisheries. The impact of El Nino depends on the existing state of the ecosystem, and may have highly significant second, third, or higher order effects.