Climate Change Is Fading the Oceans’ Greenery, Weakening Carbon Absorption, Study Finds

The world’s oceans are steadily losing their signature green hue due to global warming, raising concerns about a weakening capacity to absorb carbon dioxide, according to a new study.

Researchers attribute this color shift to a sharp decline in phytoplankton — microscopic marine organisms responsible for nearly half of Earth’s biological productivity. Using deep-learning algorithms to analyse satellite and ship-based data from 2001 to 2023, scientists found the oceans’ greenness is decreasing by about 0.35 micrograms per cubic metre annually. Coastal regions show twice the decline, and areas near river estuaries experience a drop more than four times higher.

This reduction translates to an annual 0.088% decrease in the oceans’ carbon sequestration capacity, roughly 32 million tons, said Di Long of Tsinghua University, one of the study’s authors.

Rising ocean temperatures linked to climate change are the primary culprit. Warming of surface layers has increased the temperature difference with deeper waters, disrupting the vertical nutrient flow that phytoplankton rely on. Michael Mann, a co-author from the University of Pennsylvania, stated, “This is the first study to robustly demonstrate a measurable decline in ocean greenness, signaling reduced marine productivity and another major threat posed by human-driven planetary warming.”

The study challenges earlier research suggesting a rise in oceanic algal blooms, noting that past studies were less comprehensive. While regional variations exist due to factors such as agricultural runoff, the overall trend shows a significant decline in phytoplankton across low- and mid-latitude oceans.

“These changes will profoundly affect marine ecosystem functioning and the global carbon cycle,” the researchers warned.