Quinn et al. (1978) provided a listing of El Niño
events and a measure of event intensity on a scale of 1 to
4 (strong, moderate, weak, and very weak) beginning
in 1726. The measures used to define the El Niño and
its intensity were primarily based on phenomena along
the coast of South America and were often qualitative.
In the early 1980s, a Scientific Committee for
Ocean Research working group, SCOR WG 55, was
set up to define El Niño (SCOR 1983) and came up
with the following: