Illustration: Mubari
The dark red area on the map above shows that the Pacific waters off South America are currently very warm. This is an unusual ‘coastal El Niño’ and is not related to the larger El Niños that affect global climate, says Francisco Chavez, a biological oceanographer at the Monterey Bay Aquarium Research Institute. A classic El Niño is a band of warm water that develops across the Pacific Ocean. This is in contrast to the La Niña, a band of cold water in the Pacific that has been seen over the past few years.
Models show a 62% chance of a classic El Niño by June or July, and a 4 in 10 chance of a strong El Niño. However, El Niño is not a certainty, as it is the result of complex atmospheric dynamics. Basically, the wind blows warm water from Asia. “There are still a lot of uncertainties,” he says Chavez. “Predicting a true El Niño is difficult because of the chaos in the atmosphere.”
Every El Niño has consequences. On the positive side, hurricane activity tends to be less in the Atlantic when El Niño is active in the Pacific. However, precipitation results are mixed. In Peru, El Niño tends to produce more precipitation, but could lead to devastating droughts in the Amazon rainforest to the east. And all that extra heat in the Pacific Ocean could significantly increase global temperatures. “In the event of an El Niño, 2024 will probably be warmer than 2023, as is currently considered likely.”
In the ocean itself, El Niño and global long-term heating can reduce biological productivity as water temperatures rise. Some organisms that reach their temperature limit can migrate to cooler waters, altering both the ecosystem they leave and the new one they take refuge in. Some stay in place. These animals are particularly sensitive to heat, bleaching in response to it and releasing symbiotic algae that provide energy.
The marine food chain also depends on the natural circulation of water, some of which is affected by temperature. When deep, cold water rises to the surface, nutrients grow that fertilize the phytoplankton. These microscopic plants grow in sunlight and become an important food source for small animals called zooplankton. But when the water is heated at the surface, it becomes layered and turns into a kind of cap that sits on top of the colder water below. “The long-term concern is to what extent this global heating alters natural fertilization processes such as upwelling,” Chavez says. Will the ocean become like a desert over time?”
