As ocean temperatures rise – perhaps as much as 4.8 degrees Fahrenheit in the aforementioned timeframe – the growth of the plankton will be heightened, making the blues and the greens of the ocean more vibrant, as sunlight interacts with water molecules and the blue part of the spectrum of sunlight hits it. Fewer phytoplankton cause the water to look bluer, while more give it a greener hue.
"The model suggests 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," says lead author Stephanie Dutkiewicz, a principal research scientist at MIT's Department of Earth, Atmospheric, and Planetary Sciences and the Joint Program on the Science and Policy of Global Change, in a statement. "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."
Areas that are already quite blue, especially subtropical areas (such as those between the Tropic of Cancer and Tropic of Capricorn) will become even bluer, according to the study. Regions that are nutrient-rich, including those near the poles, "may turn even deeper green, as warmer temperatures brew up larger blooms of more diverse phytoplankton."
The study was published in the scientific journal Nature Communications.
Satellites have been taking continuous measurements of the ocean's color since the late 1990s, the researchers noted. By looking at these measurements, the level of cholorophyll can be determined, which could be due to global warming or weather-related phenomena, such as an El Niño or La Niña, Dutkiewicz said.
"An El Niño or La Niña event will throw up a very large change in chlorophyll because it's changing the amount of nutrients that are coming into the system," Dutkiewicz said. "Because of these big, natural changes that happen every few years, it's hard to see if things are changing due to climate change, if you're just looking at chlorophyll."
The impact of fewer phytoplankton will have a two-fold effect: not only do they remove carbon dioxide from the air and help regulate the climate, according to separate studies, but they also provide food for other sea creatures, including zooplankton, which are food for fish.
"It could be potentially quite serious," Dutkiewicz added of the change in color in the oceans. "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. "