How do El Niño and La Niña events typically influence global rainfall and temperature anomalies?

• A. El Niño tends to increase global temperatures and shift rainfall patterns (wet in some regions, dry in others); La Niña often cools global temperatures and alters rainfall patterns in opposite ways.
• B. El Niño cools global temperatures and reduces rainfall worldwide.
• C. La Niña warms global temperatures and increases rainfall everywhere.
• D. They have no consistent influence on rainfall or temperature.

Answer: (A)

El Niño and La Niña are opposite phases of a global climate pattern (ENSO) that changes how heat is distributed in the Pacific and how weather systems travel around the world. When the Pacific Ocean warmens during El Niño, more heat escapes to the atmosphere and convection increases in the central to eastern Pacific. This shifts atmospheric circulation and jet streams, which tends to raise the global average temperature for several months to a year. The rainfall pattern also shifts: some regions become wetter while others become drier, with typical impacts like wetter conditions in parts of the Americas and drier conditions in Australia and Southeast Asia.

During La Niña, cooler surface waters in the eastern Pacific strengthen trade winds and favor different circulation patterns. This generally lowers the global average temperature and produces rainfall changes that are often opposite to El Niño—for instance, wetter conditions in areas that were drier during El Niño and drier conditions in places that were wetter.

So the typical effect is that El Niño raises global temperatures and redistributes rainfall, while La Niña cools global temperatures and shifts rainfall in the opposite way.