Scientists ring alarm bells as oceanic expansion accelerates rise of sea levels

Global sea levels rose more rapidly than anticipated in 2024, primarily due to the warming of ocean water, which caused it to expand—a phenomenon known as thermal expansion.

Unlike previous years, when melting ice was the dominant factor, thermal expansion was the main driver of last year’s increase. Data from NASA’s satellite records, which have been tracking sea levels since 1993, show a continuous upward trend, with oceanic forces such as wind patterns and El Niño significantly influencing heat distribution.

A study led by NASA determined that sea levels rose by 0.59 centimeters in 2024.

An article by SciTechDaily has published the findings of the research, highlighting that these figures exceeded the projected annual increase of 0.43 centimeters.

“The rise observed in 2024 was greater than expected,” said Josh Willis, a sea level expert at NASA’s Jet Propulsion Laboratory in Southern California. “Each year brings slight variations, but the overarching trend is clear: the ocean is steadily rising, and the pace is accelerating.”

In recent years, approximately two-thirds of sea level rise has been attributed to melting ice sheets and glaciers, while thermal expansion contributed the remaining third. However, in 2024, this pattern reversed, with ocean warming accounting for about two-thirds of the increase.

“With 2024 being the hottest year on record, the ocean is expanding accordingly, reaching its highest levels in three decades,” said Nadya Vinogradova Shiffer, who oversees physical oceanography programs and the Integrated Earth System Observatory at NASA Headquarters in Washington.

Since satellite observations of ocean height began in 1993, the annual rate of sea level rise has more than doubled, with an overall increase of 10 centimeters since then.

This long-term record has been maintained through a continuous series of ocean-monitoring satellites, starting with TOPEX/Poseidon in 1992. The latest satellite in this sequence, Sentinel-6 Michael Freilich, launched in 2020, is part of a twin satellite system designed to extend this dataset into a fourth decade. Its counterpart, Sentinel-6B, is set to continue measuring sea surface height with centimeter-level precision across 90% of the world’s oceans.

El Niño’s influence on heat distribution

El Niño, a climate pattern in which a vast region of warm water shifts from the western Pacific to the central and eastern Pacific, also plays a role in redistributing ocean heat. This large-scale water movement can lead to vertical shifts in temperature within the ocean.

How heat spreads through the Ocean

Multiple mechanisms contribute to ocean warming, leading to thermal expansion. Normally, seawater forms distinct layers based on temperature and density, with warmer, lighter water floating above cooler, denser water. The article points out that heat from the surface seeps gradually into deeper layers in most regions.

However, in areas with strong winds, ocean layers can be disturbed, allowing for vertical mixing. Powerful ocean currents, such as those in the Southern Ocean, can also tilt these layers, making it easier for surface water to sink deeper.

By Nazrin Sadigova