PACIFIC OCEAN — Projections indicate the tropical Pacific is developing toward a strong El Niño, the warm phase of an ocean-atmosphere cycle that can shift storm, fisheries, and rainfall patterns globally. A strong event over the next 12 to 18 months could push the planet's average annual temperature past the 1.5°C warming threshold identified in scientific documents and political agreements.

James Hansen said a moderately strong El Niño during the next 12 to 18 months could push the global average temperature to about 1.7°C above pre-industrial levels. Hansen doubts global temperatures will drop below the 1.5°C mark after the El Niño phase ends.

El Niño begins with periodic shifts of ocean currents and winds over the Pacific, releasing heat from the ocean into the atmosphere. During the cycle, heat from the Western Pacific Warm Pool between Australia and Indonesia surges eastward and northward toward Japan. The warm pool is the warmest ocean region on Earth and covers an area four times as large as the continental United States.

Heat spreading across the equatorial Pacific enters the atmosphere in pulses that alter weather patterns, reroute high-elevation winds, raise global temperatures, bleach coral reefs, and disrupt fisheries and ocean ecosystems. The effects can intensify rainstorms and flooding in some continental regions and amplify extreme heat, drought, and wildfires in others. A recent study shows that strong El Niño events can trigger abrupt, lasting changes in heat, rainfall, and drought patterns.

In 2015, heat from the tropical Pacific contributed to pushing the global annual average temperature past 1°C above the pre-industrial baseline. In 2024, Earth recorded its hottest year in recorded history, aided by El Niño.

Coral reefs from Australia to the Caribbean have experienced irreversible bleaching and vast forest areas have burned in large wildfires. California reservoirs sometimes fail to fill in some years and overflow with extreme rainfall in others. Traditional agricultural planting calendars no longer align reliably with seasonal weather patterns, and elevated nighttime heat in cities kills vulnerable residents in apartments that do not cool at night.

Understanding how stronger El Niños reshape the climate can help countries close the global adaptation gap, defined by the United Nations as the gap between known climate risks and actual preparation. A recent study shows that strong El Niño events can trigger abrupt, lasting changes in heat, rainfall, and drought patterns that compound these risks.