During the warm phase, this upwelling is reduced, and warm surface water spreads across the entire tropical Pacific.

With the ice age's warm phase, Neanderthal man moved into Wales, then the fringe of the human world.

These warm or cold phases take about two years to develop and play out, though each can vary in length and strength.

The settlers arrived during a warm phase, when short-season crops such as rye and barley could be grown.

Precisely what triggers a warm or cold phase is not yet perfectly understood, but scientists believe they know much about the general processes at work.

On average, each warm and cold phase takes about two years to develop and play out, though some are longer or shorter.

Each warm and cold phase also has its own profile -some are major and some are minor.

After that, if scientists are right about the new pattern, another swing toward El Nino, the warm phase, should begin.

In the 1990s, the Pacific was in a warm phase.

The strong El Niño of 1997 marked the end of the warm phase.