Scientists have discovered significant changes in the color of the world's oceans over the past two decades, potentially linked to human-induced climate change.
Researchers at the Massachusetts Institute of Technology (MIT), the National Oceanography Center in the UK, and other institutions found that changes in ocean color, which can be imperceptible to the human eye, have occurred in 56% of the Earth's oceans, surpassing the total land area on the planet.
Color of the Oceans
The study found that tropical ocean regions near the equator have become steadily greener over time, indicating potential transformations within marine ecosystems.
The color of the ocean is a reflection of the organisms and materials present in its waters, suggesting that these ecosystems are also undergoing changes.
While the exact nature of these shifts remains uncertain, the researchers are confident in the role of human-induced climate change. The findings provide further evidence of the impact of human activities on a global scale.
Stephanie Dutkiewicz, a co-author of the study from MIT, expressed her concerns regarding the observed changes, stating that "to actually see it happening for real is not surprising, but frightening. And these changes are consistent with man-induced changes to our climate."
In a statement, the study's lead author B. B. Cael PhD '19 of the National Oceanography Center in Southampton, UK, added that "this gives additional evidence of how human activities are affecting life on Earth over a huge spatial extent. It's another way that humans are affecting the biosphere."
The alterations in the ocean's color can be attributed to the composition within its upper layers. Deep blue waters generally indicate very little life, while greener waters suggest the presence of ecosystems, and phytoplankton, which are plant-like microbes that contain the green pigment chlorophyll and rely on sunlight for photosynthesis.
Phytoplankton are essential for the marine food web and play a significant role in capturing and storing carbon dioxide.
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Monitoring Phytoplankton
The researchers emphasized the importance of monitoring phytoplankton and their response to climate change. Previous studies focused on tracking chlorophyll, but the team discovered that the natural variability in chlorophyll concentrations makes it challenging to detect long-term climate change trends.
Instead, the researchers analyzed changes in multiple ocean colors captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite over a period of 21 years.
Using statistical analysis, the team detected a clear trend in ocean color changes beyond the expected natural variability. To verify its connection to climate change, they referred to a model developed in 2019 that simulated the oceans with the addition of greenhouse gases and the other without it.
The greenhouse-gas model predicted that a significant trend should show up within 20 years and that this trend should cause changes to ocean color in about 50% of the world's surface oceans. This is nearly similar to what Cael discovered in his analysis of real-world satellite data.
By monitoring ocean colors beyond chlorophyll, the team's results show scientists can gain insights into climate-change-driven changes to marine ecosystems more efficiently and faster. The study's findings highlight the need for continued research to understand and address the impacts of climate change on oceans.
"So, we hope people take this seriously. It's not only models that are predicting these changes will happen. We can now see it happening, and the ocean is changing," Dutkiewicz said.
The study's findings were published in the journal Nature on Wednesday.
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