It could happen even sooner, according to a new MIT study.

By Kimberly Holland
Updated: March 22, 2019
Roc Canals Photography/Getty Images

The world’s oceans are growing warmer and more acidic due to climate change, which will have far-reaching impacts, including a change to the color of the oceans themselves.

According to a new MIT study, 50 percent of the earth’s oceans will be a different color by the end of the 21st century, if not sooner, due to climate change. But the shade shift is just a visual signifier of larger, more serious impacts on ocean and human life.

The study, published in the journal Nature Communications, details that the change in hues will be almost imperceptible to the human eye, but satellite imagery will reveal the subtle shifts in half of the world’s 140 million square miles of ocean.

“Ocean color will give us an earlier signal of climate change effects on the marine ecosystem than other things we usually look at,” lead study author Stephanie Dutkiewicz told Discover magazine.

The color change stems from a tiny source: phytoplankton, microscopic sea algae that play a multi-pronged role in the health of our planet — and its current appearance:

1) Phytoplankton are the base of the ocean’s food chain, feeding everything from tiny zooplankton to huge whales. 2) They are responsible for removing carbon dioxide from the atmosphere, which in turn helps balance global temperatures. 3) They reflect light, making water where they are plentiful look green and water where they are not look blue.

When water temperatures warm, as they are predicted to do as climate change continues, phytoplankton will be affected. Phytoplankton thrive in cooler waters, which means as the oceans warm, phytoplankton will move to cooler waters, for example leaving the North Atlantic coast for Greenland — changing the make-up of the water and food supply.

In the MIT study, researchers created a model using satellite imagery to predict how a 3°C (5.4°F) increase in global temperatures will impact the world’s oceans, specifically with regard to the growth and interaction of different types of phytoplankton species. (This temperature increase is the amount scientists predict will occur without significant efforts to curb climate change.)

The model showed that by the year 2100, more than 50 percent of the world’s oceans will have a significant shift in color due to the effects of climate change, specifically the impact on phytoplankton populations.

Blue waters, like those in the Caribbean and other subtropics, will get bluer. That’s because phytoplankton populations, which are already low in these regions, will continue to die off due to warming waters, as will other sea life that depend on phytoplankton for survival.

Green waters, such as those around the poles, will be greener because phytoplankton populations will likely bloom in the warmer temperatures.

Why Changes to Phytoplankton Populations Herald Climate Change Consequences

As phytoplankton populations die or blossom, they will be unable to pull carbon dioxide out of the air during photosynthesis. That also means the phytoplankton won’t be releasing as much oxygen into the air, which can worsen global warming and carbon build up.

As some species of phytoplankton die off as a consequence of climate change, the ocean’s food base will be upended.

"The change is not a good thing, since it will definitely impact the rest of the food web," Dutkiewicz told CNN. "Phytoplankton are at the base, and if the base changes, it endangers everything else along the food web, going far enough to the polar bears or tuna or just about anything that you want to eat or love to see in pictures."

The Bottom Line

While the shifts in color will likely not be visible to the human eye, the consequences of those shifts could reverberate around the world, as the growing effects of global warming begin to alter the planet’s ecosystem, food sources, and well-being.

“Changes are happening because of climate change,” Dutkiewicz told The Washington Post. “It’ll be a while before we can statistically show that. But the change in the color of the ocean will be one of early warning signals that we really have changed our planet.”

Related: The Oceans Are Warming Faster Than We Thought, a New Study Says

How the Oceans Get Their Colors

Ocean color is a reflection of what’s in the water itself. Ocean water absorbs most colors, and if there’s little life in the water itself, blue light is reflected back.

Therefore, in vast, mostly unpopulated waters, the sun’s light is absorbed by water molecules, and what you (or satellites) see is brilliant blue waters.

In waters that are teeming with sea life, the color is a bit different. The microscopic phytoplankton make ocean waters appear more green. These microorganisms absorb most of the light from the sun including the blue light and use it to grow. They reflect green light thanks to the chlorophyll they create during photosynthesis.

Phytoplankton, like the trees and plants on Earth’s land surfaces, absorb a great deal of carbon from the Earth’s atmosphere.

Dutkiewicz notes that some phytoplankton changes aren’t due to climate change but are instead the result of “natural variability,” or periodic shifts in the concentration of the algae in water.

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