El Niño is characterized by which ocean temperature pattern?

• A. Unusually cold surface waters in the western Pacific.
• B. A stable global climate with no variation.
• C. Unusually warm surface waters in the eastern tropical Pacific.
• D. A periodic increase in Atlantic hurricane activity.

Answer: (C)

El Niño is defined by warm sea-surface temperature anomalies in the eastern tropical Pacific. When trade winds weaken, the warm water that typically pools in the western Pacific shifts eastward, reducing upwelling along the western coast of South America and raising surface temperatures in the eastern Pacific. That pattern of unusually warm surface waters in the eastern tropical Pacific is the hallmark of El Niño. The other options describe different, unrelated situations: cold waters in the western Pacific would imply a La Niña-like condition; a stable global climate with no variation ignores the typical ENSO fluctuations; and increased Atlantic hurricane activity is about a different ocean basin and phenomenon.