Climate Change Will Alter the Color of Half of Earth’s Oceans by 2100

Half of Earth's oceans will change color by 2100 as a result of warming global temperatures, according to a study published Monday in Nature Communications.

Blue ocean surfaces are expected to shift to a darker blue, said the authors, who were led by Stephanie Dutkiewicz, a principal research scientist and marine ecologist at MIT. Meanwhile, green-tinted marine habitats could become more intensely verdant.

The shifts in color will be the result of marine phytoplankton-microscopic organisms that live in the sunlit layers of the ocean-responding to the effects of human-driven climate change.

Phytoplankton uses the pigment chlorophyll to harvest solar radiation into energy, which bounces green rays back into the environment. As a result, large communities of phytoplankton act like a biological dye tinting the ocean surface green, while marine habitats that are depleted of phytoplankton are more of a navy blue color.

"There will be a noticeable difference in the color of 50 percent of the ocean by the end of the 21st century," Dutkiewicz said in a statement. "It could be potentially quite serious. Different types of phytoplankton absorb light differently, and if climate change shifts one community of phytoplankton to another, that will also change the types of food webs they can support."

Using computer models, the team projected that some blue regions of the ocean, including subtropical gyres, are likely to become bluer in the coming decades due to a reduced phytoplankton presence in the warmer waters. Meanwhile, phytoplankton blooms will become common in the water around Earth's poles, suggesting those regions might have an emerald shade in the coming decades.

Monitoring ocean color could yield valuable insights into the effects of climate change on phytoplankton. Not only do these organisms make up the bedrock of aquatic food webs, their photosynthetic processes produce half the world's oxygen and sequester about 10 gigatons of carbon into the deep ocean.

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Given how critical phytoplankton are to Earth's life support systems, it's alarming that rising sea temperatures have wiped out 40 percent of their population since 1950. If this trend continues, the marine food web could begin to collapse without its foundational food source. This would affect human reliance on marine species for food, sure, but it could also eventually make air less oxygenated (aka breathable) and cause runaway atmospheric carbon dioxide levels.

"Phytoplankton community structure, which strongly affects ocean optics, is likely to show one of the clearest and most rapid signatures of changes to the base of the marine ecosystem," Dutkiewicz and her colleagues said in the paper.

The projected shifts might not be discernible to the naked eye, but satellites can detect them from space. Keeping tabs on this climate-related color change will enable scientists to estimate the health of the global phytoplankton population, which is crucial to the millions of species that depend on it.

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