Study finds 56% of ocean surface greener from climate change

Research published in Nature found 56% of the world's ocean surface has turned greener over two decades, attributed to climate change. The finding signals accelerating disruption to marine ecosystems that underpin fisheries and coastal economies relevant to India's blue economy and climate adaptation planning.

New research published in Nature found that more than half of the world's oceans have turned greener over the past two decades, a shift scientists attribute to global warming. Lead author B. B. Cael of the National Oceanography Centre and his team analysed two decades of data from the MODIS sensor aboard NASA's Aqua satellite, examining seven wavelengths of light. They identified significant colour shifts across 56% of the ocean surface, predominantly in tropical and subtropical waters between latitudes 40 degrees south and 40 degrees north.

The findings affect understanding of marine ecosystems, fisheries and the organisms underpinning ocean food chains, since colour reflects chlorophyll and phytoplankton abundance. One hypothesis links the change to warming surface waters becoming more stratified, hindering nutrient upwelling and favouring smaller phytoplankton over larger species. The observed shifts aligned with model predictions of marine ecosystems responding to rising greenhouse gas levels. Coastal nations, fisheries-dependent communities and ocean-monitoring scientists are most concerned with the ecological implications of these accelerating, climate-driven changes.

Researchers and policymakers should monitor outputs from NASA's Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite, set to launch in January 2024 with hyperspectral capabilities measuring more wavelengths than any prior mission, to understand ecological implications. Indian marine scientists, fisheries managers and blue-economy planners should track these ecosystem-structure trends, given the relevance of tropical and subtropical ocean changes to Indian coastal waters, and incorporate evolving phytoplankton and productivity data into climate-adaptation and fisheries management strategies.

Key figure — Ocean surface affected: 56% showing significant colour shifts