New Delhi, July 24
Climate change has significantly altered the color of Earth’s oceans over the past two decades, according to a study.
Research recently published in the journal Nature found changes in ocean color over the past 20 years that cannot be explained by natural, year-to-year variability alone.
These color changes, though subtle to the human eye, occurred in 56 percent of the world’s oceans — an area larger than Earth’s total land area, the researchers said.
A team of researchers from the Massachusetts Institute of Technology (MIT), the US’s National Oceanography Center and the UK’s National Oceanography Center found that tropical ocean regions near the equator, in particular, have greened steadily over time.
According to the researchers, the change in ocean color indicates that the ocean’s surface ecosystems must also be changing, as the ocean’s color is a literal reflection of the organisms and materials in its waters.
It’s not certain exactly how marine ecosystems are changing to reflect the changing color, but researchers say it’s likely due to human-induced climate change.
“I’ve been running simulations for years that tell me these changes in ocean color are going to happen,” said Stephanie Dutkiewicz, a senior research scientist at MIT.
“It’s actually not surprising that this is happening, but alarming. These changes are consistent with human-induced changes in our climate,” Dutkiewicz said.
The color of the ocean is a visual product of what lies within its upper layers. Generally, deep blue water reflects little life, while green water indicates the presence of ecosystems, mainly phytoplankton — plant-like microorganisms that are abundant in the upper ocean and contain the green pigment chlorophyll.
The team analyzed ocean color measurements taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite, which has been monitoring ocean color for 21 years. MODIS takes measurements at seven visible wavelengths, including two colors traditionally used by researchers to estimate chlorophyll.
Using all seven ocean colors measured by the satellite from 2002 to 2022, the researchers performed a statistical analysis.
They first looked at how much the seven colors changed from region to region in a given year, which gave them an idea of their natural variations.
The team then zoomed out to see how these annual variations in ocean color have changed over two decades. This analysis showed a clear trend above normal year-to-year variation.