Climate change is turning the oceans greener

The phytoplankton, or small algae in the sea, modifies the color of the water. The discoveries of the researchers using long-term satellite data are concerning.

Although it is not visible to the naked eye, satellite photographs gathered over a 20-year period show a significant trend: the oceans are turning greener. According to a Nature study by a group of researchers, color change is most likely caused by a change in phytoplankton composition, which may be related to climate change.

Satellite measurements from July 2002 to June 2022 reveal that the light reflected from the oceans has altered dramatically. The tendency toward greater green light is most visible between 40 degrees north and south latitude, i.e., in the tropics and subtropics. It impacts 56% of the sea surface, which is larger than the whole land surface of the Earth.

Not surprising, but scary

The green color of phytoplankton comes from chlorophyll, a pigment that living things use to carry out photosynthesis. Changes in the amount of chlorophyll can be determined by satellite using the ratio of green to blue light. In the current analysis, the researchers also included other sea colors measured by satellites. A comparison of various computer models that simulated the color changes with and without an increase in greenhouse gases suggests that the effect is triggered by man-made climate change.

I’ve been running simulations for years and know that this kind of ocean color change is going to happen,” said study co-author Stephanie Datkiewicz said in a MIT statement. A senior scientist at the Massachusetts Institute of Technology’s Department of Earth, Atmospheric, and Planetary Sciences said, “It’s not surprising, but it’s frightening to see that actually happening. And these changes are human-induced climate change.” It’s consistent with the changes,” he said.

The observation is “additional evidence of how human activity is impacting life on Earth on vast spatial scales,” said BB Cael of the National Oceanography Center in Southampton, UK. He is the lead author of the study.