Global warming will change the colour of oceans, scientists warn

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The study predicts that the blues will intensify, most likely in subtropical regions where phytoplankton will decrease.

Writing in the journal Nature Communications, Hickman and colleagues from the United Kingdom and USA 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. While water absorbs everything except for the blue part of the spectrum, other organisms can absorb and reflect different wavelengths of light.

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]".

An MIT study is reporting that by the end of the 21st century, 50 percent of the world's ocean, will be a different color.

Phytoplankton are the base of the food web, Dutkiewicz said, and they are extremely diverse.

"The basic pattern will still be there", said Research Scientist Stephanie Dutkiewicz in a press release from MIT.

To determine this, the research team developed a global model that simulates the growth and interaction of phytoplankton and how the different species mix with a rise in temperatures as well as how the creatures absorb and reflect light. According to Pete Strutton, an Associate Professor at the Institute for Marine and Antarctic Studies at the University of Tasmania, "Phytoplankton produce half of the oxygen in the earth's atmosphere and are at the very base of the food chain".

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Climate change will likely alter the types of phytoplankton that abound in future oceans. Climate change will fuel the blooming of some phytoplankton in some areas, while reducing it in other spots, leading to subtle changes in the ocean's appearance. As a result, more green light is reflected back out of the ocean, giving algae-rich regions a greenish hue.

Since the 1990s, satellites have taken regular measurements of how much chlorophyll is in the ocean. While chlorophyll levels could be altered by the effects of global warming, natural events such as El Niño can also cause an uptick in chlorophyll.

"Sunlight will come into the ocean, and anything that's in the ocean will absorb it, like chlorophyll", Dutkiewicz says.

"If the productivity of the ocean changes, it will impact that ability".

The ocean looks blue or green to us because of a combination of how sunlight interacts with water molecules and with whatever else lives in that water. Dutkiewicz fed satellite measurements of reflected light into a computer model, and correlated it to the number and type of ocean organisms. Dutkiewicz said those instruments will probably provide early signals of how climate change is altering the oceans and their colour.

But in the scientific world, they could mean significant shifts. 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. The sensors, which measure the colour of the water, work to calibrate satellite data in real time, providing information about the health of the Salish Sea.

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