Climate Change Is Going to Change the Color of the Oceans by the End of the Century

More than 50 percent of the world's oceans will have changed color by the end of the century as a result of climate change, scientists said.

In a study published in Nature Communications, a team of researchers led by Stephanie Dutkiewicz, from the Massachusetts Institute of Technology, looked at how phytoplankton would respond to warming global temperatures over the coming decades.

Phytoplankton are microscopic, often single-celled organisms that live in water. Like other plants, they use chlorophyll to capture sunlight and turn it into energy via photosynthesis. They consume carbon dioxide and release oxygen. The phytoplankton that live in the sunlit part of the ocean are hugely important, as they serve as the base of the marine food web. They also play a role in regulating the transfer of carbon to deeper parts of the ocean, so understanding how climate change impacts phytoplankton will become increasingly important in the future.

One way to monitor changes on a global scale is through observing the color of the ocean satellite data.

Ocean color changes depending on how sunlight interacts with what's in the water. While water absorbs everything except for the blue part of the spectrum, other organisms can absorb and reflect different wavelengths of light. Phytoplankton can absorb blue, but less green. This means that in areas where numbers are high, the water appears greener.

For their study, the researchers developed a model simulating the growth and interactions of different phytoplankton species, and ran simulations based on the planet warming by 3C. This is the midrange of the level of warming expected under a "business-as-usual" scenario, where greenhouse gas emissions continue on their current trajectory, with no significant scaling back.

The team combined a system looking at changes to the hue of the ocean over the last two decades with one that predicted how phytoplankton would react to rising temperatures and ocean acidification—where the pH level of the water becomes more acidic as the ocean absorbs more carbon dioxide from the atmosphere. As a result, the simulation could show changes to the light being absorbed and reflected to the ocean based on the presence of phytoplankton.

Findings showed that changes to the color of the ocean would take place as early as 2055. The subtropics—which include California, Texas and Florida—will become more blue, while areas near the poles, where warmer temperatures will lead to more diverse phytoplankton, will become greener.

"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."

She continued, "The changes won't appear huge to the naked eye, and the ocean will still look like it has blue regions in the subtropics and greener regions near the equator and poles. That basic pattern will still be there. But it'll be enough different that it will affect the rest of the food web that phytoplankton supports."

Cuba from space
Cuba appears at the top of this high oblique image taken from the International Space Station. NASA