OCEAN ACIDIFICATION: THE HIDDEN CHANGE BENEATH THE SURFACE
The world's oceans absorb approximately one-quarter of the carbon dioxide released into the atmosphere by human activities each year. This natural process slows the rate at which carbon dioxide accumulates in the atmosphere, but it also alters the chemistry of seawater. As dissolved carbon dioxide reacts with water, it forms carbonic acid, leading to a gradual reduction in ocean pH. Although seawater remains slightly alkaline, scientists refer to this ongoing process as ocean acidification.
Ocean acidification does not affect all marine organisms equally. Species that build shells or skeletons from calcium carbonate, including many corals, oysters and some plankton, may experience greater difficulty forming and maintaining these structures as ocean chemistry changes. However, laboratory and field studies have shown considerable variation among species. Some organisms appear more tolerant of changing conditions than others, and researchers continue to investigate the reasons for these differences.
Ocean acidification rarely acts in isolation. Marine organisms are often exposed to several environmental pressures simultaneously, including rising sea temperatures, pollution and overfishing. Scientists suggest that these combined stressors may influence marine ecosystems in more complex ways than any single factor acting alone. Nevertheless, determining the relative importance of each factor remains a significant scientific challenge.
Researchers use experiments, long-term observations and computer models to investigate future changes in ocean chemistry. Although these approaches have improved scientific understanding, uncertainties remain regarding how ecosystems will respond over the coming decades. Scientists therefore avoid making absolute predictions about the future of every marine species.
Some governments and international organisations have increased investment in marine research and monitoring programmes. These initiatives aim to improve scientific understanding rather than provide immediate solutions. Experts generally agree that reducing carbon dioxide emissions would address the underlying cause of ocean acidification, while local conservation measures may strengthen the resilience of certain marine ecosystems.
Despite decades of research, many aspects of ocean acidification remain uncertain. Scientists continue to study biological adaptation, species interactions and ecosystem recovery under changing ocean conditions.
Questions 1–12
Do the following statements agree with the information given in the passage?
Write
TRUE if the statement agrees with the passage.
FALSE if the statement contradicts the passage.
NOT GIVEN if there is no information.
1. The Pacific Ocean absorbs more carbon dioxide than the Atlantic Ocean.
2. Ocean acidification occurs because dissolved carbon dioxide changes seawater chemistry.
3. Ocean acidification makes seawater acidic rather than alkaline.
4. Scientists first used computer models to study ocean acidification in the 1990s.
5. Some shell-forming organisms may find it harder to build calcium carbonate structures.
6. Every marine organism responds to ocean acidification in the same way.
7. Pollution has a greater effect on marine ecosystems than rising sea temperatures.
8. Scientists recognise that several environmental pressures can act together.
9. Researchers can accurately predict the future of every marine species.
10. The largest marine monitoring programme is operated by the United Nations.
11. Local conservation measures alone can eliminate ocean acidification.
12. Researchers are continuing to investigate how marine ecosystems respond to changing ocean conditions.
Summary
This IELTS reading passage explores the causes and consequences of ocean acidification, a major environmental challenge driven by increasing carbon dioxide absorption by the oceans. It explains how dissolved carbon dioxide changes seawater chemistry, affecting shell-forming organisms such as corals, oysters, and plankton. The passage also discusses the combined effects of ocean acidification, rising sea temperatures, pollution, and overfishing, while highlighting ongoing scientific research, marine monitoring programmes, and conservation efforts. Twelve True, False, and Not Given questions are included to help learners strengthen their IELTS reading comprehension, vocabulary, and analytical skills.