Green shading represents areas where ocean surface color has significantly changed. Black dots represent areas with a change in chlorophyll levels. NASA
Satellite images have confirmed that the world’s oceans have become slightly greener. Scientists suspect climate change may be the cause.
In a recent study published in Nature, researchers in Britain and the U.S. found that nearly 60 percent of the Earth’s ocean surface has undergone a significant change in color, especially in the lower latitudes, over the past 20 years.
Many of the areas with new hues align with areas of increased chlorophyll production, indicating greater phytoplankton abundance and activity in near-surface waters as a result of a changing climate.
But researchers don’t fully understand why oceans have become greener. They speculate that the color difference could result from more organic particles lingering on the surface, or from changing populations of microorganisms.
They know that climate change is increasing ocean stratification — keeping warmer surface layers from mixing with cooler, deeper parts of the ocean — and that those conditions affect plankton populations and surface biomass. But it is too early to tell with certainty if stratification contributes to the observed color change.
Still, the authors wrote, “Given the key role of plankton ecosystems in marine food webs, global biogeochemical cycles, and carbon cycle–climate feedbacks, detecting change in these ecosystems is of great utility.”
