Unexpected sea level rise threatens coastal ecosystems and marine biodiversity

Zawya

02-04-2025

Sea level rise is a major global issue driven by climate change, primarily due to melting ice caps and the thermal expansion of seawater.
Higher sea levels lead to more frequent and severe coastal flooding. Increased erosion have seen threatening coastal infrastructure and communities around the world.
Globally, sea level rose faster than expected in 2024, mostly because of ocean water expanding as it warms, or thermal expansion.
According to a recent Nasa-led analysis, last year's rate of rise was 0.23 inches (0.59 centimetres) per year, compared to the expected rate of 0.17 inches (0.43 centimetres) per year.
'The rise we saw in 2024 was higher than we expected,' said Josh Willis, a sea level researcher at Nasa's Jet Propulsion Laboratory in Southern California.
'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.'
In recent years, about two-thirds of sea level rise was from the addition of water from land into the ocean by melting ice sheets and glaciers. About a third came from thermal expansion of seawater. But in 2024, those contributions flipped, with two-thirds of sea level rise coming from thermal expansion.
'With 2024 as the warmest year on record, Earth's expanding oceans are following suit, reaching their highest levels in three decades,' said Nadya Vinogradova Shiffer, head of physical oceanography programmes and the Integrated Earth System Observatory at Nasa Headquarters in Washington.
Since the satellite record of ocean height began in 1993, the rate of annual sea level rise has more than doubled. In total, global sea level has gone up by 4 inches (10 centimetres) since 1993, noted Jane J Lee of Nasa's Jet Propulsion Laboratory.
According to Nasa, there are several ways in which heat makes its way into the ocean, resulting in the thermal expansion of water. Normally, seawater arranges itself into layers determined by water temperature and density.
Warmer water floats on top of and is lighter than cooler water, which is denser. In most places, heat from the surface moves very slowly through these layers down into the deep ocean.
But extremely windy areas of the ocean can agitate the layers enough to result in vertical mixing. Very large currents, like those found in the Southern Ocean, can tilt ocean layers, allowing surface waters to more easily slip down deep.
The massive movement of water during El Niño — in which a large pool of warm water normally located in the western Pacific Ocean sloshes over to the central and eastern Pacific — can also result in vertical movement of heat within the ocean.
In another report, Nasa noted the rate of global sea level rise doubled in the last 30 years.
Citing recent findings, the premier space agency said this rate measures the average rise in sea level each year — most of it resulting from climate change. The study found that in 1993, the rate was about 0.08 inches (2.1 millimetres) per year but has since increased to about 0.18 inches (4.5 millimetres) per year in 2023.
The study reports that sea level also is expected to grow by another 6.6 inches (169 millimetres) globally over the next 30 years if it follows this trend.
'We have had this succession of satellite missions over the past three decades, one building on top of another, and it's that data on a global scale that allows us to precisely track the rate of global sea level rise,' said Nasa Sea Level Change Team Principal Investigator Benjamin Hamlington, the new study's lead author.
Although a number of factors contribute to sea level rise, the primary causes are warming and ice-melt due to greenhouse gas emissions, Hamlington said.
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