Oceans are changing color, likely due to climate change, researchers find

The oceans of today look different from the oceans of 20 years ago, researchers found in a new study. 

Around 56% of the world's oceans have changed color, with the blue waters becoming greener over time, according to a study published Wednesday in the journal Nature. Tropical ocean water near the equator has been especially impacted. Scientists at the Massachusetts Institute of Technology and National Oceanography Center in the U.K. found that the change is likely driven by climate change. 

"To actually see it happening for real is not surprising, but frightening," said Stephanie Dutkiewicz, the study's coauthor and senior research scientist at MIT's department of Earth, atmospheric and planetary sciences and the Center for Global Change Science. "And these changes are consistent with man-induced changes to our climate."

The ocean's color is a product of whatever is in the upper layers of the water. It usually appears blue because the ocean acts as a sunlight filter and the water absorbs colors in the red part of the light spectrum, according to National Oceanic and Atmospheric Administration. A greener color, which the researchers found, happens when light bounces off of materials and life in the water. Greener water is largely driven by the presence of phytoplankton.

Much of the change in color is too subtle for the human eye to notice. The researchers used data from the Moderate Resolution Imaging Spectroradiometer aboard NASA's Aqua satellite — which has been monitoring ocean color for 21 years. 

Researchers wrote that the change in color over that time "suggest that the effects of climate change are already being felt in surface marine microbial ecosystems."

Dutkiewicz said that "changes in color reflect changes in plankton communities, that will impact everything that feeds on plankton." 

"It will also change how much the ocean will take up carbon, because different types of plankton have different abilities to do that," she said. "So, we hope people take this seriously. It's not only models that are predicting these changes will happen. We can now see it happening, and the ocean is changing."

The team of researchers used simulations of how the water would look both with and without the addition of greenhouse gasses to determine the role climate change played, study author BB Cael said. The model with greenhouse gasses almost exactly matched what Cael found in his analysis of real-world satellite data.

"This suggests that the trends we observe are not a random variation in the Earth system," Cael said. "This is consistent with anthropogenic climate change."

NASA is set to gather additional data on ocean color. The space agency plans to launch the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission next year. It will take global ocean color measurements to help scientists understand how the ocean and atmosphere exchange carbon dioxide.