Several repercussions of global warming seem far-flung or mild, and some are even reversible to varying degrees. It is also accurate to say that some speculations about the second or third-order effects of warming are hypotheses- although very robust- but still, just educated predictions. But one direct impact, that’s not mediated by any complex process but is the primary effect of global warming, is the ‘warming’ itself. The warming of the atmosphere and essentially our oceans-the vast blue bodies of water that cover most of our planet.
The vast portion of biodiversity on our planet is submerged under the seas, even the largest oxygen producers- planktons. But the rising temperature of the ocean water is posing a threat to marine biodiversity. All the marine organisms that are aerobic respirators use oxygen to breathe, underwater the oxygen is dissolved in the water. The ability of any liquid to retain some gas that is dissolved in it depends largely on two factors, first- temperature, second pressure. Any change in the composition of dissolved oxygen in the ocean due to human interference depends on the temperature of the water and the composition of the water itself. It is very similar to how soft drinks work, they are pressurized and stored in a cold place to retain the fizzy nature of the drink, leave the drink in a glass on a table to warm and all gas turns into bubbles and leaves the drink, making it less punchy.
The same is happening to our oceans, due to the increasing concentration of greenhouse gasses. The atmosphere traps more heat than usual, making cooling down more difficult and time-consuming. Hypoxia– lack of enough Oxygen. Ocean water is defined as the state of low oxygen at which the physiological and ecological processes are disrupted. Apart from warming, the increase in the flux of nutrients into seawater through rivers drive blooms of algae to form which eventually die and their decomposition consumes lots of dissolved oxygen.
Night time cooling is a term used for the cooling that takes place at night. The sun radiates heat in the daytime, it warms the air of that region, water on the other hand, has a higher specific heat capacity than air, which means that it takes more heat to raise the temperature of the water. The benefit of this is that water traps more heat than air keeping the surroundings cooler. The problem is, with the increase in the heat trapped in the atmosphere because of global warming, the night time atmosphere is still too warm to let enough heat escape from water. This cycle of small amounts of heat getting incrementally trapped in water with each cycle of sun ends up warming the lower levels of ocean water. As heat evenly spreads across the levels, it becomes harder to dissipate, since there are no drastically cool surroundings for the lower layers that are getting slowly heated. Thus the cycle continues. The warming of polar oceans and melting of ice further multiplies this feedback cycle’s intensity. Ice and glaciers are shiny and reflective, as the glaciers melt, they turn into dense, blue water which absorbs multiple times more heat than the shiny iceberg that it once was and that melts more of the surrounding icebergs. As the glaciers melt due to rising temperatures, it turns into non-saline water which floats over the saline sea water covering it and making aeration of water more difficult.
The deoxygenation of ocean water is not fatal for all organisms, but it significantly alters their patterns of consumption and reproduction. It also exposes the hypoxia sensitive species to the risk of predation from hypoxia tolerant species. Some species that can respire anaerobically (without the need of oxygen) can survive but anaerobic respiration is about 10 times less efficient than aerobic respiration in terms of the energy it generates. The species that are not mobile see changes in their metabolic rate, their mating patterns etc. Mobile species, on the other hand, migrate to oxygen-rich areas of the ocean changing the composition and affecting the behavior of other species in that region, for example, sharks and tunas migrate to the upper layers of the ocean, which leaves them susceptible to overfishing and human encounters.
The primary factor driving the deoxygenation is the warming of water and hypermineralization of water in some places, it develops into a positive feedback loop where organisms die and their decay consumes more oxygen dissolved in the water further driving the hypoxia. The way to stop and eventually reverse this process is to limit emissions and make systems more sustainable.
Vivek is a writer who writes to explore. His interests include philosopy, psychology, poetry, cinema, mythology and international relations. Above all he’s interested in making sense of complex systems-how they work and influence each other. An alumnus of Calcutta University, he has a bachelor's degree in Physics.
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