Climate: How This Extreme El Niño Is Changing Ocean Colors

The latest NASA satellite images reveal that a vast swath of the surface waters of the Pacific Ocean has radically changed color over the past few months, with global implications.

A dramatic decline in phytoplankton

While there are thousands of species of phytoplankton in the equatorial Pacific, these ecosystems are typically dominated by chlorophyll-rich photosynthetic organisms. Preferring cooler waters, these populations have been severely hit by the latest El Niño, characterized by higher surface temperatures that limit the upwelling of nutrient-rich waters from the depths.

The recent analysis of data from the Ocean Color Instrument, carried by the PACE satellite, revealed a massive decline in phytoplankton in this part of the globe since the start of the year. While, until the end of 2025, a broad green band stretched from South America to Southeast Asia, a few months later, it had largely thinned, with the western section almost completely gone.

Seen at first glance as a minor change, this shift in color has significant repercussions for marine ecosystems. Phytoplankton serves as an essential nutrient source for krill, zooplankton, and filter-feeding crustaceans, which themselves form the diet of much larger animals, making them crucial links in the oceanic food chain.

Combined with the global warming of the oceans, the massive die-off of these microorganisms is driving many highly targeted fish species toward cooler latitudes. This translates into reduced catches of tuna or sardines by Asian and South American trawlers, and a surge in prices worldwide.

Effects that go beyond the oceans

It turns out that El Niño also exerts influence on weather regimes, driving in particular severe droughts in some regions of the globe and heavy rainfall in others.

According to the latest data, this episode could become the most intense ever observed, with surface temperatures in the tropical Pacific already reaching record levels. Its magnitude brings it close to the 1997-1998 event, associated with 23,000 deaths and an estimated economic loss of 5.7 trillion dollars.