CANBERRA – Stronger El Nino events in the future could cause irreversible melting of ice shelves and sheets in Antarctica, raising global sea levels, Australian research has concluded.

El Nino is the warmer phase of the El Nino Southern Oscillation (Enso) that occurs over the tropical eastern Pacific Ocean, and with the colder phase, La Nina, influences weather conditions around the world.

El Nino typically brings drier and hotter weather to South-east Asia and eastern Australia, raising the risk of forest fires.

The new study, published on Tuesday by the Commonwealth Scientific and Industrial Research Organisation, Australia’s national science agency, demonstrated that the variability of Enso reduces warming near the surface of the ocean but accelerates warming of deeper waters.

Dr Cai Wenju, lead author of the study, said the findings were critical to furthering the understanding of how Antarctica will be affected by climate change.

This is because rising temperatures there are already leading to faster melting of ice, especially in West Antarctica.

The West Antarctic Ice Sheet would raise sea levels by about 3m if it were to melt completely. Some large glaciers in West Antarctica are already losing huge amounts of ice every year.

“Climate change is expected to increase the magnitude of Enso, making both El Nino and La Nina stronger,” said Dr Cai.

“This new research shows that stronger El Nino may speed up warming of deep waters in the Antarctic shelf, making ice shelves and ice sheets melt faster.”

Ice sheets are on land, while ice shelves are the large floating front edges of glaciers like tongues of ice, which can be hundreds of metres thick.

The concern is that rapid melting of the ice shelves will speed up the discharge of ice from the glaciers on land into the sea, rather like removing a cork from a bottle.

Dr Cai said the modelling also revealed that warming around the edges of floating sea ice is slowed during this process, slowing down the melting of sea ice near the surface. Dr Cai and his team examined 31 climate models under a high-emissions scenario.

Those with increased Enso variability showed a reduced upwelling of deep, warmer water as a result of less intense westerly winds, leading to a slower warming of the ocean surface.

Co-author Ariaan Purich from Monash University said that Enso variability could have broad implications for the global climate.

“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. XINHUA