Kids may be using different shades of blue and green Crayolas to color their pictures of the ocean by the end of the 21st Century, according to a new Massachusetts Institute of Technology study. Researchers from MIT developed a model to simulate the growth and interaction of different types of phytoplankton and algae, observing how changing temperatures of the ocean over the coming decades will influence the mixing of those species. They also simulated how phytoplankton absorbs and reflects light, learning that climate change will effectively alter the ocean’s coloring near the surface.
“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,” said lead author Stephanie Dutkiewicz in a statement. Dutkiewicz is 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. “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.”
By the year 2100, they say more than 50 percent of our oceans will have shifted in color, and those regions in the subtropics and near the equator and poles will have brighter blues and deeper greens most visible through satellite images of the Earth. Scientists have been constantly recording the ocean’s colors via satellite images since the 1990s as a way to measure the amount of chlorophyll, and by extension, phytoplankton in the water. They’re able to do this because water absorbs most sunlight with the exception of blue parts of the spectrum, which is reflected back out. Because phytoplankton absorbs much of those blue portions to produce carbon for photosynthesis and less of the green portions, areas of the ocean that are rich in algae end up having more of a greenish hue.
“Sunlight will come into the ocean, and anything that’s in the ocean will absorb it, like chlorophyll,” Dutkiewicz says. “Other things will absorb or scatter it, like something with a hard shell. So it’s a complicated process, how light is reflected back out of the ocean to give it its color.”
Researchers used the past satellite images to develop a model that would predict phytoplankton changes with rising temperatures and ocean acidification. Their model can estimate wavelengths of light that are absorbed and reflected by the ocean, which obviously changes by a given region and the organisms in the water. Under the assumption that climate change will continue at its expected rate throughout the 21st century, they then cranked up the ocean temperatures in their model by three degrees Celsius, which is what most scientists predict will happen under a scenario in which there’s relatively no action taken to reduce greenhouse gases. That simple adjustment in their model gave more intense hues of green and blue.
“Chlorophyll is changing, but you can’t really see it because of its incredible natural variability,” Dutkiewicz says. “But you can see a significant, climate-related shift in some of these wavebands, in the signal being sent out to the satellites. So that’s where we should be looking in satellite measurements for a real signal of change.”