What is the reason why the 'La Niña phenomenon', which causes floods and droughts due to the decrease in seawater temperature, has continued for a long time?

Large-scale floods have occurred in eastern Australia due to the '

La Niña phenomenon ,' in which sea surface temperatures continue to be lower than normal from the vicinity of the International Date Line in the Pacific equatorial region to the coast of South America. Climatologists predict that the La Niña phenomenon 'will last for three years,' and consider the cause.

Rare'triple' La Niña climate event looks likely — what does the future hold?

In 2022, it was reported that the La Niña phenomenon caused floods in eastern Australia and worsened drought in the United States and East Africa. This La Niña phenomenon may continue until 2023, according to the latest forecasts. It is said that the La Niña phenomenon often occurs in the Northern Hemisphere for the second consecutive year, but it is relatively rare for it to occur for the third consecutive year, and the La Niña phenomenon for the third consecutive year has occurred only twice since 1950.

Prolonged La Niña creates more cumulonimbus clouds in the waters near Indonesia, increasing the risk of floods in Southeast Asia and droughts and wildfires in the southwestern United States. In addition, hurricanes, cyclones and monsoon patterns will change in the Pacific and Atlantic Oceans, bringing about changes in other regions as well.

The La Niña phenomenon that occurred in 2022 has continued since around September 2020, and its effects have been mild to moderate. However, in April 2022, the La Niña phenomenon intensified, and the eastern equatorial Pacific Ocean experienced cold waves that had not been seen during this period since 1950.

According to the latest forecast of the World Meteorological Organization released on June 10, 2022, there is a 50-60% chance that the La Niña phenomenon will continue from July 2022 to September 2022. For this reason, the activity of the Atlantic hurricane that hits eastern North America will increase until November, and the Pacific hurricane that mainly affects Mexico is expected to decrease. The National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center predicts a 51% chance of a La Niña event in early 2023.

According to the latest report of the Intergovernmental Panel on Climate Change (IPCC), the strong El Nino and La Nina phenomena have occurred more frequently and more strongly since 1950 than in the centuries before that, but at the IPCC. It is not known if this is due to natural or climate change. 'The IPCC model shows that as climate change warms the ocean, it moves closer to the Ernino phenomenon,' said Richard Seager, climate modeler at Columbia University's Lamont Doherty Earth Observatory in Paris, New York. Pointed out. However, observations over the last half century show the opposite. As the climate warms, the waters of the eastern equatorial Pacific become colder, creating a state closer to the La Niña phenomenon.

Some scientists argue that there are too few records to be clear about what is happening, or that natural fluctuations are too great to capture long-term trends. However, it has also been pointed out that the IPCC model may have missed something big. 'The model is certainly wrong, and I think the Earth will experience more of the La Niña-like conditions in the future. More and more people are seriously thinking that the model may be biased. I'm coming. '

Matthew England, a marine physicist at the University of New South Wales, Australia, offers another possibility why the IPCC model misunderstands situations like the future La Niña phenomenon. As the world warms and the Greenland ice sheet melts, the fresh cold water is expected to slow down one of the ocean current systems, the Atlantic meridional overturn (AMOC), according to England.

England and colleagues modeled and analyzed a situation in which the collapse of AMOC left excess heat in the South Atlantic Ocean, which caused a series of pressure changes that ultimately strengthened the Pacific trade winds. The Pacific trade winds push warm seawater to the west, creating a state similar to the La Niña phenomenon, but according to England, the current IPCC model is between ice sheet melting, freshwater injection, ocean currents, and atmospheric circulation. It does not seem to reflect this trend because it does not contain the complex interactions of. Michael Mann, a climatologist at State College, Pennsylvania, also argues that climate change delays AMOC and creates a state closer to La Niña.

'It is still a very active research subject to better reflect what is happening in the ocean in the model,' said Seger, emphasizing the need to renew the computational model.

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