Scientists figured this out by creating a global model that simulates the growth of a tiny creature that lives in the oceans and affects the color we see.
Phytoplankton are small, microscopic plants that float through the water column, due to their ability to absorb and reflect light, communities of phytoplankton affect the color of the ocean. Nitrogen also plays a key role in regulating the global carbon cycle.
Hickman said: "Crudely speaking, where the water is now quite blue because the phytoplankton [have a] relatively low biomass, you are going to see the water getting more blue, and where the ocean is relatively more green because the biomass is higher, you are going to see [it] getting [greener]".
Phytoplankton contain chlorophyll, a pigment which absorbs the blue portions of sunlight to produce carbon for photosynthesis.
Writing in the journal Nature Communications, Hickman and colleagues from the United Kingdom and U.S. report how they came to their conclusions by using a computer model that predicts how factors such as temperature, ocean currents and ocean acidity affects the growth and types of phytoplankton in the water, as well as levels of other coloured organic matter and detritus. And when phytoplankton blooms to deep green, it indicates a diversification in species due to increased carbon dioxide and heat.
"Other things will absorb or scatter it, like something with a hard shell". Now, the computer simulation is able to estimate specific wavelengths of light absorbed and reflected by the ocean depending on the amount and type of organism in a given region. That gets reflected back out, giving it its deep blue color.
"Looking at just the colour of the ocean, and how that is going to change in the future by monitoring it from satellites, is actually going to give us an early warning signal of changes in the phytoplankton", said Hickman. The resulting model can be fed with various values of inputs, primarily global temperatures.
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Climate change is already having profound effects on our planet, and here's one more: It's changing the color of the oceans, with the blues getting bluer and the greens getting greener.
"Chlorophyll is changing, but you can't really see it because of its incredible natural variability", Dutkiewicz says.
The team, which includes researchers from MIT, University of Southhampton, National Oceanography Centre Southampton, University of California at Santa Cruz, and University of California at Davis, states that the new model shows that the effects of climate change on the oceans is far more rapid than expected. "But you can see a significant, climate-related shift in some of these wavebands, in the signal being sent out to the satellites".
Since the 1990s, satellites have taken regular measurements of how much chlorophyll is in the ocean. As such, life in these areas as we know it today is likely to also change.
Climate change will bring a color change to half of the world's oceans by the end of the21st century, the study says.
As well as changes in the blue of the oceans, we are also likely to see changes in the green.
"There will be a noticeable difference in the color of 50 percent of the ocean by the end of the 21st century", Dutkiewicz says. "It could be potentially quite serious". "But it'll be enough different that it will affect the rest of the food web that phytoplankton supports".