Nasa: Sea levels rose more than expected in Earth’s hottest year

• Global sea levels rose 5.9mm in 2024, exceeding the predicted 4.3mm due to ocean warming and meltwater.
• NASA reported 2024 as the hottest year on record, with two-thirds of sea level rise from thermal expansion.
• Sea levels have risen 10.1cm since 1993, primarily due to glacier melting and thermal expansion.

Global sea levels rose more than expected in 2024, Earth’s hottest year on record, according to an analysis released Thursday by the US space agency Nasa.

On its website, the National Aeronautics and Space Administration explained that last year’s increase “was due to an unusual amount of ocean warming, combined with meltwater from land-based ice such as glaciers”.

According to the analysis led by Nasa, which monitors rising water levels using satellite imagery, the world’s seas rose by 0.23 inches (0.59cm) in 2024, well above the 0.17 inches (0.43cm) predicted by scientists.

“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,” said researcher Josh Willis of Nasa’s Jet Propulsion Laboratory.

Rising sea levels are among the consequences of human-induced climate change, and oceans have risen in line with the increase in the Earth’s average surface temperature – a change which itself is caused by greenhouse gas emissions.

Over a recent three-decade period, from 1993 to 2023, average sea levels around the globe have risen by some 4 inches (10cm) in total, according to Nasa.

In NZ, houses in low-lying areas around the country are exposed to the risk from sea-level rise in the coming decade. Photo / Ben Cowper

The phenomenon is caused primarily by two factors: the melting of glaciers and polar ice caps, which increases the flow of freshwater into oceans; and the expansion of seawater due to heat, a process known as thermal expansion.

In recent years, the observed rise in sea levels has been mainly caused by the first factor and less by the second, according to Nasa.

“But in 2024, those contributions flipped, with two-thirds of sea level rise coming from thermal expansion,” the agency said.

The year 2024 was the warmest on record since such record-keeping began in 1850.

Sea levels are expected to rise further as humanity continues to emit greenhouse gases, threatening vast populations living on islands or along coastlines.

- Agence France-Presse