“The rise we saw in 2024 was higher than we expected,” says Josh Willis, a scientist for sea level at NASA’s Jet Propulsion Laboratory. This is the tone of the feeling of urgency in the new information to report that global sea levels increased by 0.23 inches over the last year, more than had been forecast. The increase, primarily because of thermal expansion of seawater, follows the dynamic interaction between oceanic currents and atmospheric heat.
The process of thermal expansion, or expansion of water when it gets heated, has been the subject of modern-day interest. Previously, ice sheets and glaciers melting were humongous contributors to sea-level increases. But in 2024, the pattern was reversed where two-thirds of the increase resulted from thermal expansion. The reason behind this switch is the record temperatures of 2024, which became the hottest year yet. Indeed, according to NASA’s Nadya Vinogradova Shiffer, “Earth’s expanding oceans are following suit, reaching their highest levels in three decades.”
We must understand which processes have brought about this expansion. Sea water will stratify into temperature and density layers, with warm over colder denser layers. This stratification may be broken, however, by powerful winds and large ocean currents, which bring about vertical mixing that spreads heat downwards. Weather phenomena like El Niño, where warm water moves eastward across the Pacific, distribute this heat as well, contributing to the effects of thermal expansion.
The implications of the findings are extensive. Sea level rise holds extensive risks for coastal communities, habitats, and infrastructure. According to a report by NASA, the additional acceleration in 2024 has risks to marine ecosystems and freshwater resources and can induce mass movements. It is a call to action against greenhouse gas emissions to avoid worsening the damage.
Satellite technology has played a key part in tracking such changes. Since 1993, a series of ocean-monitoring satellites have given essential data about sea level behavior. But the legacy continues with satellite Sentinel-6 Michael Freilich launched in 2020, which offers the accurate GPS-measured sea surface height. Its twin, the upcoming Sentinel-6B, will continue the record further, charting some 90% of the oceans of the world. But satellite technology has also given ocean-related data.
The long-term record from the satellites carries a worrisome message: the rate of sea level rise per year has picked up more than twice since 1993. On average, sea levels worldwide have risen 4 inches in that time. That news suggests acceleration of the transition and the value of continued observation of climate change effects.
For residents of coastal villages, the stakes are most direct. Sea level rise exacerbates the risk of flooding, shoreline erosion, and storm surges. In the United States alone, it is estimated that almost 30% of the country’s population lives in coastal areas, and they are vulnerable. Additionally, as the U.N. Atlas of the Oceans notices, eight out of the world’s ten most populous cities are on or along a coastline, imparting global proportions to this issue.
Mitigation strategies for the effects of these changes will cover greenhouse gas mitigation to reduce emissions, as well as increasing coastal resilience. Use of renewable energy, such as solar power, to diminish reliance upon vulnerable power grids can be done. Local causes of sea-level rise, including ground settling and local ocean currents, can also be understood to create adaptation strategies designed by their particular contribution.
The results in 2024 are a wake-up call to climate action. As the globe warms further, impacts on our oceans and coastal cities will only deteriorate. By harnessing the force of science and technology, we can be more ready to find out what these changes are and take sensible steps to ensure our future.
