How Climate Change Affects Oceans — Reading Comprehension

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MS-ESS3-5

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This NGSS-aligned passage explores major changes occurring in Earth’s oceans, focusing on the mechanisms and impacts of ocean warming and acidification. Students will learn how the ocean absorbs excess heat and carbon dioxide from the atmosphere, leading to rising temperatures, lower pH levels, and significant consequences for marine life and global systems. The passage explains scientific evidence, processes like coral bleaching and the formation of carbonic acid, and the broader implications for food webs and climate. Activities include comprehension questions, writing prompts, and graphic organizers to deepen understanding. Designed for grades 6-8, this resource integrates academic vocabulary, systems thinking, and real-world connections. Audio integration supports diverse learners, and the included Spanish translations foster accessibility for bilingual students. This comprehensive package supports the development of scientific literacy and critical thinking, making it ideal for middle school science classrooms.

CONTENT PREVIEW

Dynamic aerial view of ocean waves crashing against rocky structures, captured from above. — The world’s oceans act as a massive carbon sink. Image by Sebastian Voortman / Pexels.

Earth’s oceans are undergoing significant changes that affect both marine life and global climate systems. Scientists have observed that the oceans are warming and becoming more acidic, raising questions about the future of the planet’s largest ecosystem. Understanding the mechanisms driving these changes is essential for predicting their impact on biodiversity, weather patterns, and human societies.

Warming Oceans: The Heat Sink Effect

The world’s oceans act as a massive heat sink, absorbing over 90% of the excess heat generated by human-caused greenhouse gases. As a result, ocean temperatures have risen steadily in recent decades. This warming leads to more frequent and intense marine heat waves, which can devastate ecosystems. For example, warmer water causes coral bleaching, where stressed corals lose their symbiotic algae and turn white, often leading to death. Fish populations are also shifting their ranges poleward in search of cooler waters, which disrupts food webs and fisheries. Additionally, warmer oceans provide more energy for stronger hurricanes and tropical storms, increasing risks for coastal communities.

Ocean Acidification: A Chemical Shift

Another major change is ocean acidification. The ocean absorbs about 25% of human carbon dioxide emissions each year. When CO₂ mixes with seawater, it forms carbonic acid, lowering the water’s pH and making it more acidic. Since the pre-industrial era, the ocean has become about 30% more acidic. This chemical change makes it harder for shell-forming organisms—such as corals, oysters, and pteropods (tiny sea snails)—to build and maintain their shells. In some cases, existing shells can even dissolve in the more acidic water. These changes threaten the food web, as creatures like pteropods are a vital food source for many fish species.

Interactions and Broader Impacts

Warming water also holds less dissolved oxygen, leading to low-oxygen areas called "dead zones" where many marine organisms cannot survive. Scientists are also studying how warming and changes in salinity could slow down major ocean circulation patterns, which transport heat and nutrients around the globe. These disruptions could affect weather, climate, and food supplies far beyond the ocean itself. By monitoring ocean chemistry, temperature, and animal populations, scientists use data and models to predict future changes and inform conservation efforts.

Understanding ocean changes requires a systems approach, linking chemistry, biology, and climate. The health of the ocean is deeply connected to life on land, making it vital to protect and preserve this vast and dynamic system.

Interesting Fact:
Some scientists call pteropods "the potato chips of the sea" because so many fish and whales depend on them for food!

What percentage of excess heat produced by greenhouse gases is absorbed by the ocean?

Over 90%About 50%Less than 25%Around 10%

What is coral bleaching?

A process where corals lose their algae and turn white due to stressCorals growing faster because of warm waterThe formation of new coral reefsWhen fish eat all the coral

How much more acidic is the ocean compared to pre-industrial times?

About 30% more acidicAbout 5% more acidicTwice as acidicNo change

What is a food web?

A network showing who eats whom in an ecosystemA kind of fishing netA group of ocean currentsA map of ocean temperatures

Which of the following best describes 'marine heat waves' as used in the passage?

Periods when ocean water is unusually warm for days to monthsGiant waves caused by hurricanesA pattern of strong winds over the oceanTimes when fish swim in groups

What is the function of pteropods in the ocean food web?

They are a vital food source for many fishThey provide oxygen to the waterThey filter out pollutionThey build coral reefs

Why does warmer water lead to 'dead zones'?

Because warmer water holds less dissolved oxygenBecause it creates more coral reefsBecause more fish swim thereBecause it increases the salt content

If ocean currents slow down due to warming and salinity changes, what might happen?

Weather, climate, and food supplies could change worldwideCoral reefs will grow fasterMore whales will appearOcean pH will rise

True or False: Ocean acidification makes it easier for shell-forming organisms to build their shells.

TrueFalse

True or False: Scientists use data and models to predict future changes in the ocean.

TrueFalse