Study: Oceans are changing color, and climate change is likely to blame

Over 56% of the world's oceans have subtly changed color over the past 20 years and human-caused climate change is likely to blame.

Driving the news: That's according to a new study from scientists at the Massachusetts Institute of Technology and National Oceanography Centre in the U.K. that found the phenomena can't be explained by natural variability alone.

What they did: For the study, published in the journal Nature on Wednesday, researchers analyzed data from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Aqua satellite as color changes can be too subtle for the human eye to detect.

What they found: Tropical ocean regions near the equator have been particularly affected by this steady change from blue to green, according to the research.

• "The shift in ocean color indicates that ecosystems within the surface ocean must also be changing, as the color of the ocean is a literal reflection of the organisms and materials in its waters," per a statement from MIT accompanying the study.
• The results "suggest that the effects of climate change are already being felt in surface marine microbial ecosystems," the study notes.

Between the lines: "Much of the ocean appears blue to our eye, whereas the true color may contain a mix of subtler wavelengths, from blue to green and even red," per MIT.

• "Generally, waters that are deep blue reflect very little life, whereas greener waters indicate the presence of ecosystems, and mainly phytoplankton — plant-like microbes that are abundant in upper ocean and that contain the green pigment chlorophyll."

Of note: Study co-author Stephanie Dutkiewicz, a senior research scientist at MIT’s Department of Earth, Atmospheric and Planetary Sciences and the Center for Global Change Science, said in a statement that researchers couldn't say how ocean colors had changed.

• "But we can say that changes in color reflect changes in plankton communities, that will impact everything that feeds on plankton," she said.
• "It will also change how much the ocean will take up carbon, because different types of plankton have different abilities to do that," Dutkiewicz added. "It's not only models that are predicting these changes will happen. We can now see it happening, and the ocean is changing."

What they're saying: Kevin Trenberth, a distinguished scholar at the National Center for Atmospheric Research, said in an email to Axios Thursday the findings related to a 2020 study he was involved in showing the upper global ocean has become more stratified and stable over the past few decades with global warming.

• Trenberth, who was not involved in the latest study, noted that the researchers "do not sort out the large effects" of the El Niño-Southern Oscillation (ENSO) and that the past three years had been dominated by a major La Niña event.
• However, Trenberth called the study "a useful start to detailing the consequences of the upper ocean changes and marine ecosystems associated with climate change."

More from Axios:

• A crucial year for understanding how ocean warming affects marine life
• Ocean heat content hits record high, a sign of global warming
• Concerns mount over the speed of key climate change trends