Published: 20:15, February 24, 2023 | Updated: 20:58, February 24, 2023
Study: Intense El Niño expected to speed up sea level rise
By Karl Wilson

This file photo dated Aug 17, 2019 shows Los Laureles reservoir rationing water supply because of the reservoir low level due to El Niño phenomenon. (PHOTO / AFP)

Stronger El Niño weather patterns may speed up the “irreversible melting” of ice shelves and icesheets in Antarctica which would have a significant impact on global sea levels, according to new research.

The research led by scientists from the Commonwealth Scientific and Industrial Research Organisation, Monash University in Melbourne and the University of New South Wales adds to a growing body of scientific work warning that Antarctic ice melt will see ocean levels rise which will have a catastrophic impact on low lying island nations in the Pacific.

A recent report by the BBC said there is now less sea ice surrounding the Antarctic continent than at any time since scientists began using satellites to measure it in the late 1970s

A recent report by the BBC said there is now less sea ice surrounding the Antarctic continent than at any time since scientists began using satellites to measure it in the late 1970s.

READ MORE: Report: Sea levels to rise 25 to 30 cm by 2050, rate 'alarming'

The latest report, published on Feb 20 in the science journal Nature Climate Change, used climate models to show how an increase in the variability of El Niño Southern Oscillation leads to reduced warming near the surface, but accelerated warming of deeper ocean waters.

ENSO is a key driver of climate variability, as both its warm phase, El Niño, and its colder phase, La Niña, influence weather conditions around the world, including in Australia.

Wenju Cai, lead author of the study and global expert on the relationship between climate change and ENSO, said the research was a critical step in further understanding how Antarctica will be affected by climate change.

“Climate change is expected to increase the magnitude of ENSO, making both El Niño and La Niña stronger,” Cai said in a statement.

“This new research shows that stronger El Niño may speed up warming of deep waters in the Antarctic shelf, making ice shelves and ice sheets melt faster,” said Cai who is chief research scientist with the CSIRO and director of Southern Hemisphere.

“Models with increased ENSO variability show a reduced upwelling of deeper, warmer waters, leading to slower warming of the ocean surface,” he said.

The associated winds around Antarctica are the mechanism driving this result. When ENSO variability increases, it slows the intensifying westerly winds along the shelf. As a result, the upwelling of warm water around Antarctica is not able to increase as much.

Co-author Ariaan Purich from Securing Antarctica’s Environmental Future at Monash University said the effects of increasing ENSO variability go beyond extreme weather risks, and affect changes in Antarctic sea ice and ice shelves and sheets.

“This could have broad implications for the global climate system, so continuing to understand how ENSO will respond to climate change is a critical area of climate research,” Purich said.

“There is still a lot more we need to understand about processes influencing shelf temperatures, and the finding is an important piece of the puzzle," she said.

In an interview with the China Daily Cai said since 1993, global sea level has increased by around 10 cm. 

He says that during this time the Antarctic Ice Sheet has lost 2670 billion tons of ice, equivalent to 7.4 millimeters of global mean sea level rise, that is, some seven percent of the total global sea level rise.

“The melting has been speeding up,” he said.

“It is expected that this part will increase dramatically going into the future, as the shelf ocean warming accelerates melting the ice sheet. At the moment, however, there is no firm quantification.”

He said global sea level rise will lead to more coastal inundation for all coastal cities.

“The Pacific island countries are more vulnerable than most, because they are already low-lying.”

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He said increased El Nino/La Nina amplitude in the future “will not only make the mean sea level higher but also create extreme sea level anomalies that ride over the higher mean sea level over California in the US, Peru, Ecuador, Chile during El Nino, and over western Pacific countries (China, Malaysia, Bangladesh, Indonesia, Singapore) during La Nina.

Cai said attempts to cut greenhouse gas emissions have not been effective “as emissions of CO2 and its concentration in the atmosphere show no sign of decreasing.”

“Measures are not strong or fast enough, it seems. Even if we stabilize the emissions, the committed warming from the increased CO2 would drive a continuous increase in extreme weathers for a further century, though the increase will be smaller than without actions,” he said.

“Even without greenhouse warming, Antarctic climate fluctuates substantially. As such, it is difficult to separate the signal of climate change impact from natural fluctuations, more so because observations are sparse.”

The Guardian said on Feb 16 in a report that scientists have been concerned with Antarctic ice melt as far back as 2014 when the giant West Antarctic Ice Sheet, which sits on the continent, was doomed to collapse due to the levels of global heating already seen then.

“I have never seen such an extreme, ice-free situation here before,” said Prof Karsten Gohl, from the Helmholtz Centre for Polar and Marine Research in the Alfred Wegener Institute, Germany, and who first visited the region in 1994, told The Guardian.

“The continental shelf, an area the size of Germany, is now completely ice-free. It is troubling to consider how quickly this change has taken place.”

Christian Haas, also at the Helmholtz Centre, said: “The rapid decline in sea ice over the past six years is quite remarkable, since the ice cover hardly changed at all in the 35 years before.”