Rising sea levels are the long-term increase in the average height of Earth's oceans, driven by two mechanisms in the AP Environmental Science CED: melting land-based ice sheets adding water to the ocean, and thermal expansion as warming seawater takes up more space (EK STB-4.E.1, Topic 9.4).
Rising sea levels means the average height of the ocean is going up over time, and on the AP exam you need to know exactly why. The CED (EK STB-4.E.1) gives you two causes, and you should be able to name both. First, melting ice sheets. Land-based ice (think Greenland and Antarctica) melts and that water flows into the ocean, adding volume that wasn't there before. Second, ocean water expansion. Water expands as it warms, so a warmer ocean literally takes up more space even without any new water added. That second one is the one most people forget.
Both causes trace back to the same root: excess greenhouse gases trapping heat in the atmosphere. So rising sea levels aren't a standalone problem. They're a downstream effect of global climate change, sitting in the same EK as poleward-spreading disease vectors. The CED also flags the human side: flooded coastlines push people to move, which changes population dynamics and drives population movements. For the full greenhouse gas picture, head up to the Topic 9.4 study guide.
Rising sea levels live in Unit 9: Global Change, Topic 9.4 (Increases in the Greenhouse Gases) and directly support learning objective AP Enviro 9.4.A: identifying the threats to human health and the environment posed by an increase in greenhouse gases. This is one of the most concrete, name-able consequences of climate change in the whole CED, which makes it a go-to answer when a question asks you to identify or describe an environmental threat from greenhouse gases. It also connects climate science to people. The essential knowledge explicitly says these problems can change population dynamics and trigger population movements, so a strong answer links the physical cause (melting ice, thermal expansion) to a human or ecological consequence (coastal flooding, displaced communities, lost habitat).
Keep studying AP Environmental Science Unit 9
Climate Change (Unit 9)
Rising sea levels are an effect, not a cause. Greenhouse gases trap heat, the planet warms, ice melts and oceans expand. If an exam question asks for a consequence of climate change, sea level rise is one of the cleanest cause-and-effect chains you can write.
Ocean Acidification (Unit 9)
Same culprit, totally different mechanism. Excess CO2 raises sea levels by warming the planet, and it acidifies the ocean by dissolving into seawater and forming carbonic acid. Knowing that one gas drives two separate ocean problems is exactly the kind of dot-connecting Unit 9 rewards.
Coastal Erosion (Unit 9)
Higher seas mean waves and storm surge reach farther inland, eating away at shorelines faster. Sea level rise is the slow background trend; coastal erosion is one of the visible damages it accelerates.
Human Population Dynamics (Unit 3)
EK STB-4.E.1 ties sea level rise directly to changes in population dynamics and population movements. When coastal areas flood repeatedly, people relocate. That's a Unit 9 cause producing a Unit 3 effect, a classic cross-unit link for FRQs.
On multiple-choice questions, rising sea levels show up as the answer to stems like "Which environmental issue is directly linked to the increase in greenhouse gases?" or "What is a direct effect of ocean water expansion due to climate change?" You also get applied scenarios, like a coastal community facing more frequent flooding, where you have to trace the flooding back to greenhouse gases and identify the threat to human health or population movement that follows. On FRQs, sea level rise often appears in coastal ecosystem scenarios. Released free-response questions about the piping plover (2019) and Common Tern (2025) center on threatened shorebirds whose beach nesting habitat is exactly the kind of low-lying coastal area squeezed by rising seas. To earn points, you need to do more than name the term. State the mechanism (melting ice sheets and/or thermal expansion) and connect it to a specific consequence, like habitat loss, flooding, or human displacement.
Both are ocean consequences of excess CO2, so they get blended together constantly. Rising sea levels are a physical change in ocean volume caused by warming (melted land ice plus thermal expansion). Ocean acidification is a chemical change in ocean pH caused by CO2 dissolving directly into seawater. Acidification would still happen even if the planet somehow didn't warm, because it comes from the CO2 itself, not the heat. On the exam, match the mechanism to the problem: heat → sea level rise, dissolved CO2 → acidification.
Rising sea levels have two causes you must name on the exam: melting land-based ice sheets adding water to the ocean, and thermal expansion of seawater as it warms.
This term lives in Topic 9.4 and supports learning objective AP Enviro 9.4.A, which asks you to identify threats from increased greenhouse gases.
Melting floating sea ice does not raise sea levels; only ice that melts off of land (like Greenland and Antarctic ice sheets) adds water to the ocean.
EK STB-4.E.1 connects sea level rise to human consequences, specifically changes in population dynamics and population movements as coastal flooding displaces communities.
Don't mix it up with ocean acidification, which is a pH change from dissolved CO2, while sea level rise is a volume change from heat.
On FRQs, sea level rise is a strong answer for threats to coastal habitats, like the beach-nesting shorebirds featured in released questions.
Rising sea levels are the long-term increase in average ocean height caused by global climate change. The CED (EK STB-4.E.1) lists two mechanisms: melting ice sheets and the expansion of ocean water as it warms.
No. Floating sea ice already displaces its own weight in water, so when it melts, sea level barely changes (think of ice melting in a glass of water). Sea levels rise when land-based ice sheets, like those on Greenland and Antarctica, melt and add new water to the ocean.
Rising sea levels are a physical change (more ocean volume from heat and melted land ice), while ocean acidification is a chemical change (lower pH from CO2 dissolving into seawater). Both stem from excess CO2, but through completely different mechanisms.
Water expands as it warms, so when greenhouse gases trap heat and the ocean absorbs it, the same amount of seawater takes up more space. This raises sea level even without any new water entering the ocean, and the CED names it as one of the two causes of sea level rise.
Per EK STB-4.E.1, sea level rise leads to changes in population dynamics and population movements. In practice, that means more frequent coastal flooding pushes communities to relocate, which is a common answer in scenario-based questions about coastal towns.