Ocean’s green life force is fading: global warming drives sharp decline in marine plant life that feeds ocean food webs

A troubling new chapter in climate change’s impact on our planet has emerged from the depths of our oceans. Scientists have discovered that Earth’s seas are literally losing their green color as warming waters drive down populations of phytoplankton—the microscopic plant-like organisms that form the foundation of all marine life.

Published in Science Advances, the study reveals that ocean chlorophyll concentrations have declined significantly over the past two decades, with coastal areas experiencing the steepest drops. This “ocean greenness” serves as a crucial indicator of phytoplankton health, and the implications stretch far beyond color changes. These tiny organisms are the ocean’s primary producers, converting sunlight into energy and supporting everything from small fish to massive whales in the marine food web.

The culprit behind this ecological shift is rising sea surface temperatures caused by fossil fuel emissions. As ocean waters warm, they become more stratified—creating distinct temperature layers that prevent nutrient-rich deeper waters from mixing with surface waters where phytoplankton thrive. Without these essential nutrients, phytoplankton populations crash, leaving less food available for the entire ocean ecosystem.

“It’s not good,” warns Princeton University professor Curtis Deutsch, who wasn’t involved in the research. “It almost certainly means that there’s less production of new organic matter, of algae in the ocean.” While researchers don’t expect a sudden ecological collapse, the steady decline threatens global fisheries and marine biodiversity. The findings underscore yet another way that climate change is fundamentally altering Earth’s life-support systems, this time striking at the very base of ocean food webs.