For climate scientists reviewing a Pacific Ocean temperature forecast map in November, a bright red, sideways "V", thousands of kilometres long signalled disaster.

Combined with La Nina cooling in the central and eastern Pacific, the V-shaped pattern of warm seawater, stretching from Australia's east coast to the Philippines and back over the ocean north of Hawaii, indicated that halfway around the world in the Horn of Africa the upcoming March-May rainy season would likely fail.

The scientists' organisation, called...