Over the course of the 21st century, climate change will likely impact the color of about half the Earth’s oceans. Subtropical oceans will appear bluer, and those at the equator and poles will become more green in color as temperatures rise, .
The color of oceans depends on how sunlight interacts with whatever is in the water. It can be used, therefore, to gauge changes in marine life. Microscopic marine algae, or phytoplankton, serves as the base of many aquatic food webs. Not only is it a key indicator of marine health, but it’s also prevalent and therefore visible via satellite imagery.
During photosynthesis, the chlorophyll in the phytoplankton absorbs the blue light on the spectrum, making algae-rich regions appear greener. In areas where there is less phytoplankton and, in some cases, less life in general, the ocean will appear more blue because water molecules absorb all but the blue light on the spectrum.
The team behind the study, led by Stephanie Dutkiewicz, principal research scientist at MIT’s Department of Earth, Atmospheric, and Planetary Sciences, developed a computer simulation of global phytoplankton communities that reflects how the growth, interaction, and density of these populations will change because of rising ocean temperatures. When they ran the simulation through the year 2100, the model displayed a marked change in the color of more than 50 percent of the planet’s oceans.
Scientists have been charting satellite imagery to measure chlorophyll as an indicator of phytoplankton in various regions since the 1990s. While changes in chlorophyll counts could be a result of climate change, they can also be impacted by normal weather events, such as El Niño, that happen every few years. So Dutkiewicz and her team decided instead to focus specifically on satellite images of “wavelengths of light that are absorbed and reflected by the ocean, depending on the amount and type of organisms” present.
The results from their model simulations mirrored what existing satellite images had shown, proving that the model can be used to predict changes in phytoplankton levels as a result of warming seas. Better yet, complex experiments can now be conducted by running various environmental scenarios through the simulator, which could help scientists predict how the planet’s oceans will change in the future.
Already, the team’s observations have resulted in new projections for “climate-driven change” to Earth’s phytoplankton communities. While evidence based on chlorophyll measurements suggested a significant shift by 2055, the blue/green wavelengths project that change to take place much sooner. “That’s where we should be looking,” , “for a sign of real change.”
While it’s unsettling enough to imagine our blue planet turning algae-green in some places and deep-dead-blue in others, we can’t forget what the changing colors represent: irreversible alterations to entire marine food webs, and our planet’s ocean ecosystems as a whole.