Graphic showing La Nina

The La Niña weather phenomenon is under way for the third year running, the first time in more than 20 years that a “triple dip” has occurred, putting countries already affected by floods and drought on alert.

La Niña involves the cooling of the Pacific Ocean’s surface, which drives changes in wind and rainfall patterns in different areas. Typically it results in more rain in places such as Indonesia and Australia, and an increase in Atlantic hurricane activity, but also drier conditions in parts of the US, South America and Africa.

In the Atlantic, the recent hurricane in Puerto Rico caused severe flooding and left more than a million people with no electricity.

The phenomenon over the past two years has also contributed to a severe drought in parts of Africa, which has caused famine in countries including Somalia. The resulting humanitarian disaster is likely to be exacerbated by the global energy and food price inflation crises, aid agencies have warned.

Diagram showing how La Niña affects global weather systems

The Bureau of Meteorology in Australia, one of the countries regularly affected by the weather pattern, this month declared that La Niña was officially under way for the third consecutive year.

That would constitute the first triple dip since 2001, according to Michelle L’Heureux, a scientist at the US National Weather Service’s Climate Prediction Center.

Three consecutive La Niña events is “pretty unusual,” said L’Heureux, adding that there were only a handful of examples in the historical record, such as the last one between 1998-2001. The paucity of triple dip examples meant “we can’t use them to say anything about the impact or strength of this upcoming one,” she said.

Graphic showing La Nina

Australia’s Bureau of Meteorology said this La Niña event “may peak during the spring and return to neutral conditions early in 2023.” It would “increase the chances of above-average rainfall for northern and eastern Australia during spring and summer,” it added. This follows severe recurring flooding suffered along its east coast at the start of this year that may have permanently displaced communities.

At the same time, the World Meteorological Organisation has concluded that the five years to 2022 were the fourth warmest five-year period on record. The three hottest have all occurred since 2015.

Ocean heat content — a measurement of heat stored in the ocean — was also higher during the period than for any other five-year stretch, the group said.

According to data from the US National Oceanic and Atmospheric Administration, oceans in the northern hemisphere recorded their third-warmest August since 1880, when records began, compared with the 20th century average. That came as much of the world experienced record heatwaves, including large swaths of Europe.

Much of the excess heat that has built up in the Earth’s atmosphere as a result of climate change is absorbed by the ocean, which warms the water and contributes to sea levels rising.

“All data sets agree that ocean warming rates show a particularly strong increase in the past two decades,” the WMO said.

Methodology for the NOAA Coral Reef Watch historic baseline is here

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