Climate: La Nina is back and will break more temperature records

The excessive heat of the past year has raised concern. El Nino, the natural weather phenomenon that added to the warming process and made 2023 the warmest year on record, has come to an end, paving the way for the likely return in the coming months of the opposite cyclone, La Nina, synonymous with temperatures lower globally, informs AFP. But this cooling could be, on average, very weak, climatologists warn, due to warming caused by greenhouse gas emissions caused by human activities, already responsible for increasing global temperatures by at least 1.2 degrees Celsius, on average , in relation to the end of the 19th century.

El Nino is the cyclical phenomenon of warming water in the central and eastern tropical Pacific Ocean, which influences precipitation, winds and ocean currents and causes global average temperatures to rise. It appears at two to seven years of age and generally lasts between nine and 12 months. The most recent El Nino, which began in June 2023, ranked among the five most intense phenomena of this type ever measured, according to the World Meteorological Organization (WMO). Under normal conditions, the trade winds over the Pacific Ocean blow westward along the Equator, carrying warm waters from South America to Asia. To replace them, cold water rises from the depths. But during El Nino, these trade winds decrease in intensity and the warm water is sent back to the Americas, fueling further warming of the atmosphere and a southward movement of the "Pacific Jet Stream" ). That shift in the jet stream generally translates into drier weather in Southeast Asia, Australia, South Africa and northern South America, and conversely much wetter conditions in the Horn of Africa and in the southern United States. Climate change influences the ENSO cycle, but its effect remains unclear, explained Michelle L'Heureux, a specialist in this phenomenon at the US National Oceanic and Atmospheric Administration (NOAA). Drier or wetter conditions caused by ENSO "may be amplified" by global warming, she added. The increase in global temperatures that this phenomenon causes is also "a window into the future" of climate change: "by providing a temporary boost, ENSO gives us a small picture of what a warmer world means", she explained.

Although El Nino has weakened, the first four months of 2024 continued to break heat records, a fact that is not surprising, as its cycle generally leads to rising temperatures in the year following its occurrence. According to the WMO, there is a 40% chance that the July-September quarter will remain a neutral period between the two cycles, followed by a 30% chance in August-November, with the likelihood of a La Nina increasing as 2024 continues to move towards its end.

The La Nina phenomenon results in a cooling of the eastern Pacific Ocean during a period between one and three years, producing opposite effects to El Nino on the global climate. La Nina generally produces wetter conditions in parts of Australia, Southeast Asia, India, southeastern Africa, and northern Brazil, but drier conditions in parts of South America. This phenomenon may also contribute to a more violent hurricane season in the Atlantic Ocean. The American agency NOAA anticipates an exceptional 2024 season, with four to seven major hurricanes (at least category 3). The possible return of the La Nina phenomenon already this summer will not be enough to produce a cooling in the regions of Southeast Asia, affected by extreme heat waves since March.