Far beyond the colossal glaciers: the "hidden culprit" that raises sea levels even without new ice blocks melting: the ocean also warms, expands, and takes up more space.

Far beyond the colossal glaciers: the “hidden culprit” that raises sea levels even without new ice blocks melting: the ocean also warms, expands, and takes up more space.

Written by Romário Pereira de Carvalho

Published on 13/06/2026 at 12:29

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Beyond glacier melting, ocean thermal expansion helps explain why sea level continues to rise, even without direct water increase in some coastal regions

Sea level rise does not only occur when glaciers melt or ice blocks fall into the ocean. A less visible factor also contributes to this process: seawater warms, expands, and occupies more space, a phenomenon known as thermal expansion.

Sea level rise: Thermal expansion explains part of the ocean’s increase

Thermal expansion occurs when a body increases in volume when heated. In the case of the ocean, water absorbs heat, its molecules move more and slightly apart, causing the same amount of water to occupy more space.

On a small scale, like in a glass or a pot, this increase may seem almost imperceptible. But when the process occurs in an entire ocean, the effect becomes relevant to the global sea level.

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Oceans absorb more than 90% of retained heat

According to NASA, more than 90% of the heat retained by greenhouse gases has been absorbed by the oceans. This heat is stored in both surface and deep layers of the water.

The problem is that this energy does not disappear. By remaining in the ocean, it warms the water and directly contributes to thermal expansion. This is one of the main factors behind the global sea level rise.

The most common image associated with ocean advancement is that of melting glaciers. However, thermal expansion shows that part of the process happens less visibly, below the surface and on a planetary scale.

Melting also matters, but works differently

Sea level rise is mainly explained by two processes: the melting of land ice and the thermal expansion of the ocean.

When glaciers or ice caps from Greenland and Antarctica melt, the water that was on land flows into the sea. In this case, there is a direct increase in the volume of ocean water.

Floating sea ice, such as part of Arctic ice, has a smaller direct impact on sea level when it melts. This is because this ice was already displacing water while floating.

Thermal expansion has a different characteristic: it occurs without adding new water to the ocean. What changes is the space occupied by the existing water.

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Impact varies according to each coastal region

Sea level does not rise the same way everywhere. Besides ocean warming and ice melting, other factors interfere with the behavior of each coast.

Among them are ocean currents, winds, changes in Earth’s gravity, land subsidence, and tectonic movements. Therefore, two coastal cities may face different rates of rise.

In areas where the land sinks, for example, the perception of sea rise can be more intense. In other regions, changes in ocean currents or the shape of the coastline can also alter local effects.

In Chile, a country with thousands of kilometers of coastline, understanding these processes is important for coastal planning, port infrastructure, erosion, storms, and the future of seaside communities.

Thermal expansion shows that the ocean not only receives heat from climate change. It also stores this heat and responds physically to it, occupying more space and contributing to a silent, gradual, and persistent rise in sea level.

This article was prepared based on information from NASA and the provided source material, with data, numbers, and statements preserved as per the consulted material.

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Far beyond the colossal glaciers: the “hidden culprit” that raises sea levels even without new ice blocks melting: the ocean also warms, expands, and takes up more space.

Beyond glacier melting, ocean thermal expansion helps explain why sea level continues to rise, even without direct water increase in some coastal regions

Sea level rise: Thermal expansion explains part of the ocean’s increase

Oceans absorb more than 90% of retained heat

Melting also matters, but works differently

Impact varies according to each coastal region

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Beyond glacier melting, ocean thermal expansion helps explain why sea level continues to rise, even without direct water increase in some coastal regions

Sea level rise: Thermal expansion explains part of the ocean’s increase

Oceans absorb more than 90% of retained heat

Melting also matters, but works differently

Impact varies according to each coastal region

Engineers want to carve through Africa with a giant canal to bring water from the world’s second-largest river to a dying lake on the edge of the Sahara Desert that has already lost 90% of its water.

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