In this article, You will read Ocean Acidification: Causes & its Effects – for UPSC IAS.

Ocean Acidification

  • Ocean acidification has been called the “evil twin of global warming” and “the other CO2 problem”.
  • Ocean acidification is the ongoing decrease in the pH of the Earth’s oceans, caused by the uptake of carbon dioxide (CO2) from the atmosphere.
  • An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers, and lakes.
  • To achieve chemical equilibrium, some of it reacts with the water to form carbonic acid(H2CO3).
  • Some of these extra carbonic acid molecules react with a water molecule to give a bicarbonate ion and a hydronium ion, thus increasing ocean acidity (H+ ion concentration).
  • CO2 reacts with water molecules (H2O) and forms the weak acid H2CO3 (carbonic acid). Most of this acid dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). The increase in H+ ions reduces pH (measure of acidity) and the oceans acidify, that is they become more acidic or rather less alkaline. This process is called ocean acidification.
  • Checking CO and CO2 emissions and controlling pollution are the only means to reduce ocean acidification.
ocean acidification upsc

Eutrophication leads to large plankton blooms, and when these blooms collapse and sink to the sea bed the subsequent respiration of bacteria decomposing the algae leads to a decrease in seawater oxygen and an increase in CO2 (a decline in pH).

What changes in the pH of ocean has occurred?

On the pH scale, which runs from 0 to 14, solutions with low numbers are considered acidic and those with higher numbers are basic. Seven is neutral. So far, ocean pH has dropped from 8.2 to 8.1 since the industrial revolution and is expected to fall another 0.3 to 0.4 pH units by the end of the century.

But this is just a small change in pH. Is it that worrisome?

A drop in pH of 0.1 might not seem like a lot, but the pH scale, like the Richter scale for measuring earthquakes, is logarithmic. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. Many chemical reactions, including those that are essential for life, are sensitive to small changes in pH. In humans, for example, normal blood pH ranges between 7.35 and 7.45. A drop in blood pH of 0.2-0.3 can cause seizures, comas, and even death. Similarly, a small change in the pH of seawater can have harmful effects on marine life, impacting chemical communication, reproduction, and growth.

Okay, but ocean absorbing CO2 is good for the atmosphere as it reduces global warming. So, why is there a need to worry?

Initially, many scientists focused on the benefits of the ocean removing this greenhouse gas from the atmosphere. At first, scientists thought that this might be a good thing because it leaves less carbon dioxide in the air to warm the planet. But in the past decade, they’ve realized that this slowed warming has come at the cost of changing the ocean’s chemistry.

Equally worrisome is the fact that as the oceans continue to absorb more CO2, their capacity as a carbon storehouse could diminish. That means more of the carbon dioxide we emit will remain in the atmosphere, further aggravating global climate change. ocean acidification will reduce the ocean’s capacity to absorb anthropogenic CO2, which will exacerbate climate change.

Consequences of Ocean Acidification

  • Plastic pollution, overfishing, global warming, and increased acidification from burning fossil fuels means oceans are increasingly hostile to marine life
  • Ocean acidification will affect corals. This will, in turn, affect one million species that have made corals their homes.
  • Coral reefs will erode faster than they can rebuild. When shelled organisms are at risk, the entire food web may also be at risk.
  • Some algae and seagrass may benefit from higher CO2 concentrations, as they may increase their photosynthetic and growth rates.
  • Most marine species seem to be more vulnerable in their early life stages.
  • Changes through acidification will be made worse by climate change, pollution, coastal development, over-fishing, and agricultural fertilizers.
  • These changes will affect the many services the ocean provides to us.

Effects of Ocean Acidification on Corals

  • Oceans are an important reservoir for CO2, absorbing a significant quantity of it (one-third) produced by anthropogenic activities and effectively buffering climate change.
  • The uptake of atmospheric carbon dioxide is occurring at a rate exceeding the natural buffering capacity of the oceans.
  • Increasing acidity depresses metabolic rates and immune responses in some organisms.
  • Seawater absorbs CO2 to produce carbonic acid, bicarbonate, and carbonate ions.
  • However, the increase in atmospheric CO2 levels leads to a decrease in pH level, an increase in the concentration of carbonic acid and bicarbonate ions, causing a decrease in the concentration of carbonate ions.
  • The decrease in the amount of carbonate ions available makes it more difficult for marine calcifying organisms, such as coral (calcareous corals) and some plankton (calcareous plankton), to form biogenic calcium carbonate.
  • Commercial fisheries are threatened because acidification harms calcifying organisms that form the base of the Arctic food webs.
  • Increasing acidity accentuates coral bleaching as corals are very sensitive to changes in water composition.
Ocean Acidification and Corals

Impact of Ocean Acidification on Cloud Formation

  • The majority of sulphur in the atmosphere is emitted from the ocean, often in the form of dimethylsulfide (DMS) produced by phytoplankton.
  • Some of the DMS produced by phytoplankton enters the atmosphere and reacts to make sulphuric acid, which clumps into aerosols, or microscopic airborne particles.
  • Aerosols seed the formation of clouds, which help cool the Earth by reflecting sunlight.
  • But, in acidified ocean water, phytoplankton produces fewer DMS.
  • This reduction of sulphur may lead to decreased cloud formation, raising global temperatures.
Artificial Cloud seeding
  • Cloud seeding is the process of spreading either dry ice or more commonly, silver iodide aerosols, into the upper part of clouds to try to stimulate the precipitation process and form rain.
  • Since most rainfall starts through the growth of ice crystals from super-cooled cloud droplets in the upper parts of clouds, the silver iodide particles are meant to encourage the growth of new ice particles

Socio-economic Impacts


  • Ocean acidification has the potential to affect food security.
  • By 2100, the global annual costs of mollusc loss from ocean acidification could be over US$100

Coastal protection

  • Marine ecosystems such as coral reefs which protect shorelines from the destructive action of storm surges and cyclones will be affected.
  • Ocean acidification is affecting the coastal estuaries and waterways.


  • This industry could be severely affected by the impacts of ocean acidification on marine ecosystems
  • Acidification could damage the Arctic tourism economy and affect the way of life of indigenous peoples.

Carbon storage and climate regulation

  • The capacity of the ocean to absorb CO2 decreases as ocean acidification increases.
  • More acidic oceans are less effective in moderating climate change.

Ocean Acidification in Indian Ocean

  • The Arabian Sea is witnessing acidification of its surface waters, a consequence of excessive carbon dioxide in the atmosphere
  • The ocean acidification in the northern Bay of Bengal is mainly due to pollutants mixing with seawater from the Indo-Gangetic plains.
  • During winter, air blowing from land to the sea carries all pollutants with the wind and deposits in the ocean during transit.
  • Study shows rapidly decreasing presence of marine phytoplankton in the western Indian Ocean.
  • A report warns that the Indian Ocean may be reduced to an ecological desert, given the levels of ocean warming.
  • The ocean acidification in the Arabian Sea and Bay of Bengal will devastate one of the most pristine, most fertile regions, the Indian Ocean.

Way Forward

  • Reducing global greenhouse gas emissions (mitigation) is the ultimate solution to ocean acidification
  • Improvements in water quality: Monitoring and regulating localized sources of acidification from runoff and pollutants such as fertilizers.
  • Development of sustainable fisheries management practices: Regulating catches to reduce overfishing
  • Sustainable management of habitats: Increasing coastal protection, reducing sediment loading, and applying marine spatial planning.
  • Substantial research on Climate engineering to know the feasibility and impacts of its approaches.
  • Educate or sensitize the common citizens on the risks posed by climate change and ocean acidification.
  • Reducing the consumption of carbon-oriented energy sources.

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Sir, i have one doubt . Is it sufficient for the UPSC prelims

Mohmad Ashraf

Thanx so much for providing such brilliant notes sir

Mohmad Ashraf

Just recently I knew about this site ….mind-blowing notes…..really


Please complete the notes of history


Hello sir, 1stly thanku for great content, I have one query, should we download as pdf or we have to follow on web only