TOPLINE
Some 56% of the world’s oceans have become greener over the last two decades, and it’s probably because of human-caused climate change, according to a new study published Wednesday in the journal Nature that could offer clues about how climate change is impacting the ocean’s ecosystem.
KEY FACTS
The researchers in the study used satellite imagery to detect changes in color across the ocean from 2002 to 2022, and found tropical areas near the equator, mostly between the latitudes of 40º south and 40º north, have steadily become greener.
The scientists said this discovery is surprising because they previously expected they’d need over 30 years of data to spot signs of climate change in the color of the oceans, but they were able to spot it with just 20 years’ worth.
There are many reasons the ocean might change color, but the researchers said year-to-year variability in the color of the oceans alone cannot explain such drastic changes.
The researchers were unable to identify exactly why the color was changing, but theorized it might have to do with how nutrients are distributed in the ocean—as the Earth becomes warmer, the upper layers of the ocean become more stratified, making it harder for nutrients, which feed green phytoplankton, to rise to the surface.
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While they were unable to say the exact cause of the change, the scientists believe climate change is the driver of the change.
KEY BACKGROUND
The color of the ocean is vital to understanding the broader ecosystem, said B. B. Cael, the study’s lead author and an ocean and climate scientist at the National Oceanography Centre in the U.K. “The reason we care about the colour is because the colour tells us something about what’s happening in the ecosystem,” Cael told Nature in a piece accompanying the study. The authors said the ocean’s color could affect phytoplankton populations by changing how much light enters the ocean. This ultimately could impact ocean biodiversity, fisheries and the ability of the ocean to store carbon, they concluded. “Our findings therefore might be of relevance for ocean conservation and governance,” they wrote in the study.
CONTRA
The study’s authors caution that it’s still possible this change is the result of a big natural swing rather than climate change. They said they’ll need around 40 years of data to say conclusively that climate change is to blame.
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CRUCIAL QUOTE
“We are affecting the ecosystem in a way that we haven’t seen before,” Cael, said.
WHAT TO WATCH FOR
The next big satellite mission to observe ocean color. The authors of the study said one of the challenges was that they had to use multiple different satellites that all measured ocean color in different ways. But an upcoming NASA satellite mission will offer more uniform measurement, helping researchers understand how climate change is impacting the oceans. Set to launch in January 2024, this new satellite will use “hyperspectral” imaging to observe ocean color, which will allow it to see more wavelengths than any previous satellite.
FURTHER READING
Global climate-change trends detected in indicators of ocean ecology (Nature)
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