Ocean Expansion Becomes the Leading Cause of Sea Level Rise

It’s not just the rising waters that are alarming scientists - it’s what’s causing them.

For the first time, thermal expansion of the oceans - the swelling of water due to heat - has overtaken ice melt as the primary driver of sea level rise. This historic shift was revealed in a NASA study published in March 2025.

In 2024, global sea levels rose by 0.59 cm, well above the 0.43 cm initially projected. This acceleration is directly linked to record-breaking ocean temperatures recorded that year - the highest since measurements began in 1850.

Until recently, melting glaciers and polar ice caps were the main contributors to sea level rise. Now, it is heat alone causing the oceans to expand.

While thermal expansion has long been known, its growing dominance is concerning:

It means that even without additional ice melt, warming water alone can significantly raise sea levels.

Since 1993, the oceans have risen by 10 cm, and the pace is steadily increasing. If greenhouse gas emissions continue unchecked, this trend could accelerate even further - threatening millions of people living on coastlines, as well as critical infrastructure, farmland, and entire ecosystems.

As NASA researcher Josh Willis puts it:

“What’s clear is that the ocean keeps rising, and the rate of rise is getting faster.”