More than 56 percent of the world’s oceans, larger than Earth’s total land area, have changed significantly over the past two decades, and human-caused climate change is likely the cause, according to researchers. These color changes, subtle to the human eye, cannot be explained simply by natural, year-to-year variability, researchers from the Massachusetts Institute of Technology (MIT), US, and other institutions, write in their paper published in the journal Nature. ,
In regions near the equator the color of the ocean, which is a literal reflection of the life and material in its waters, was found to be consistently greener over time, indicating ecosystem changes within the surface oceans. The green color of sea water comes from the green pigment chlorophyll present in phytoplankton, which are plant-like microbes abundant in the upper ocean. Therefore, scientists are keen to monitor phytoplankton to see their response to climate change.
However, the authors of this study have shown through previous studies that tracking chlorophyll changes will take 30 years before showing climate-change-driven trends, as natural, annual variations in chlorophyll will overwhelm those affected by human activities. . In a 2019 paper, study co-author Stephanie Dutkiewicz and colleagues showed that monitoring other marine pigments, whose annual variations are much smaller than those of chlorophyll, would give more clear signals of climate-change-induced changes and They can be. Clear in 20 years instead of 30.
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“Rather than trying to estimate just one number from bits of the spectrum, it is worthwhile looking at the whole spectrum,” said lead author Bibi Kail, from the National Oceanography Centre, Southampton, UK. Cal and the team conducted a statistical analysis of all seven ocean colors recorded by satellite observations from 2002 to 2022. He initially studied the natural variations of colors by observing how they changed regionally in a given year. They then looked at how these annual variations changed over two decades.
To understand climate change’s contribution to all of these changes, they used Dutkiewicz’s 2019 model to simulate Earth’s oceans under two scenarios – one with greenhouse gases and the other without them. The greenhouse-gas model predicted a change in color for about 50 percent of the world’s surface oceans in less than 20 years — which is close to Keel’s findings from real-world satellite data analysis. “This suggests that the trends we are seeing are not a random change in the Earth system,” Kael said. “It’s consistent with anthropogenic climate change.”
“I’ve been running simulations for years that tell me these changes in ocean color are going to happen,” said Dutkiewicz, senior research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “To see this actually happening is not only surprising, but frightening. And these changes are consistent with human-induced changes in our climate,” he said.