The rate of the rise in global sea levels in 2024 surpassed the projected amount by a little over 35 percent, surprising scientists with a recorded increase of 0.23 inches (0.59 centimeters) per year, instead of the expected rate of 0.17 inches (0.43 centimeters) per year. This acceleration is due to a combination of increased meltwater from glaciers and the expansion being experienced by the oceans as they warm, with both effects being a direct consequence of global warming.

“The rise we saw in 2024 was higher than we expected,” explained Josh Willis, a sea level researcher at NASA’s Jet Propulsion Laboratory. The rate of sea level rise has doubled in the 32 years since satellite records of ocean levels began in 1993, and is now an average of four inches (10 centimeters) higher than it was then.

“Every year is a little bit different, but what’s clear is that the ocean continues to rise, and the rate of rise is getting faster and faster,” Willis added.

In previous years, the influx of meltwater from melting glaciers and ice sheets was responsible for two-thirds of sea level rise, while thermal expansion caused one-third; but last year the inverse appears to have occurred, with meltwater causing one-third and thermal expansion two-thirds. This isn’t to say that glacial melt has slowed in any way, but rather the warming of the oceans has outpaced the thaw of our cryosphere.

Water is extremely efficient at absorbing and storing thermal energy, and the world’s oceans are estimated to have absorbed about 90 percent of the heat that had been captured by the excess carbon dioxide in the atmosphere. On one hand, this has helped delay the effects of global warming for those of us that live on land; on the other hand, that thermal energy didn’t just go away, but has been circulating throughout the world’s oceans for years.

This has resulted in effects such as coral bleaching through thermal stresses being placed on reefs; more frequent and intense tropical storms as the stored heat energy circulates from the ocean back into the atmosphere; and increased flooding during both high tides and storm-generated tidal surges that are made worse by the now-accelerated increase in sea level heights.

“With 2024 as the warmest year on record, Earth’s expanding oceans are following suit, reaching their highest levels in three decades,” according to Nadya Vinogradova Shiffer, head of physical oceanography programs and the Integrated Earth System Observatory at NASA.