Published in the Nature journal, NASA satellite data paints a concerning image of the world’s oceans turning green. Studying the readings, gathered by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the ‘Aqua’ satellite, of 20 years, it has been found that over 56 per cent of the oceans have turned green in between 2002 to 2022. The study has also observed that the change in colour has been mainly concentrated near the tropics. To put things into perspective, that is a region larger than the entirety of our land masses.
The change of oceans turning green is likely attributed to human-induced climate change.
The study, ‘Global climate-change trends detected in indicators of ocean ecology’, was carried out by BB Cael and Stephanie Henson of the United Kingdom-based National Oceanography Centre, along with Kelsey Bisson of the Oregon State University Emmanuel Boss of the University of Maine, and Stephanie Dutkiewicz of the Massachusetts Institute of Technology (MIT), all US-based institutions.
Appearing mostly blue to the human eye, the ocean emits a mix of various wavelengths from blue to green to red. However, the Modis-Aqua satellite can register wavelengths of 36 bands of the electromagnetic spectrum including visible light and infrared radiation.Therefore, it can observe changes imperceptible to the human eye, leading to such disconcerted results.
The change in colour is primarily influenced by the phytoplanktons present in the surface waters of the sea, but the scientists involved in the study are of the opinion that the scale at which it is happening is an outcome of climate change. If a region of the ocean is majorly lifeless, it will appear as deep blue, whereas, a region colonised by phytoplanktons would lead to a greener tint in the surface water.
Phytoplanktons form the base of the marine food-chain and can be considered as the plants of the marine ecosystem, since they, too, contain the green-coloured pigment called chlorophyll and require sunlight to survive. They are responsible for absorbing a significant amount of carbon dioxide from the atmosphere and generating about 50 per cent of the world’s oxygen.
In a balanced ecosystem, the phytoplanktons are a source of food for various little marine creatures like snails and jellyfish, they can also become a source of concern if their population begins to surpass the equilibrium. Experiencing a population blast, they can form Harmful Algal Blooms (HAL) that look like foam and paint, and generate malignant compounds negatively impacting the local marine ecosystem.
Stephanie Dutkiewicz, a co-author of the study, had been running similar simulations at MIT, factoring in the role of humans in aggravating climate change. Those simulations had also been predicting a similar outcome for years now.
BB Cael, the lead author, also emphasises upon the role of humans in this development. “This gives additional evidence of how human activities are affecting life on Earth over a huge spatial extent”, he says.
Apart from assisting oceans in storing carbon, phytoplanktons also act as a source of energy for various marine organisms resulting in a healthy fish population for the fisherfolk to earn their livelihood. Therefore, dealing with this issue is simply not that of ecological importance but also of economic relevance.
Using the findings of the study, regions in the open ocean can be identified and then be established as protected marine areas under the United Nations High Seas Treaty.
Furthermore, NASA is launching the Mission PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) in January 2024 to better understand the role of aerosols in boosting the growth of phytoplanktons, which could then equip us with information to prevent our oceans turning green.
