Researchers from the Massachusetts Institute of Technology (MIT) and other institutes have found that over 56 percent of the world's oceans have experienced significant color changes in the past two decades, likely due to human-caused climate change. The study, published in the journal Nature, reveals that these color shifts, although subtle to the human eye, cannot be solely explained by natural variability.
Ocean color serves as an indicator of the life and materials present in its waters. The researchers discovered that regions near the equator have progressively turned greener over time, signaling ecosystem changes within the surface oceans. The green hue is attributed to the presence of chlorophyll, a pigment found in phytoplankton, which are abundant microorganisms in the upper ocean. Monitoring phytoplankton and their response to climate change is of great interest to scientists.
However, previous studies demonstrated that it would take approximately 30 years of monitoring chlorophyll levels to observe climate-change-driven trends due to the dominance of natural annual variations. To address this, the researchers proposed monitoring other ocean colors that exhibit smaller annual variations, which could provide clearer signals of climate-change-induced changes within 20 years. Lead author B. B. Cael from the National Oceanography Center and the research team conducted statistical analyses of seven ocean colors recorded by satellite observations between 2002 and 2022. They initially examined the regional changes in these colors on an annual basis and then evaluated how these variations evolved over the two-decade period. To determine the contribution of climate change to these color changes, Cael utilized a model developed by co-author Stephanie Dutkiewicz in 2019. The model simulated the Earth's oceans under two scenarios: one with greenhouse gases and the other without. The results showed that approximately 50 percent of the world's surface oceans would experience color changes within 20 years, aligning with Cael's conclusions drawn from real-world satellite data analysis.
The findings strongly suggest that the observed trends are not random variations but consistent with anthropogenic climate change. Dutkiewicz, a senior research scientist at MIT's Department of Earth, Atmospheric and Planetary Sciences, emphasized that simulations conducted over the years have consistently predicted such changes in ocean color. In conclusion, this study provides compelling evidence that human-caused climate change is responsible for significant color changes in over half of the world's oceans. The research underscores the importance of monitoring multiple ocean colors to better understand and assess the impacts of climate change on marine ecosystems.
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