Science for the Planet
Alex Rose-Innes
Researchers can now predict El Niño and La Niña events months in advance mitigating some of its harmful effects. However, the future of this global pacemaker is poorly understood. According to Eric Hand from Science, the historical record is too limited to show a change.
However, with scientific knowledge, extreme weather events across the globe – droughts (El Nino) and floods (La Nina) events) – can now be predicted months in advance. El Niño helped make 2023 the hottest year in history by a huge margin. “Every time there’s an El Niño event, all kinds of weird funky things happen,” says Pedro DiNezio, a paleoclimate modeler at the University of Colorado Boulder.
Global Weather patterns written in coral
Ancient corals could reveal how the extreme events will behave in the future. “The way forward is to bring paleo data to bear on this,” says Gabriel Vecchi, climate scientist at Princeton University.
El Niño and La Niña events are sparked by fluctuations in intensifying trade winds, causing drought and downpours along the Pacific Rim and elsewhere, able to change global temperatures by 0.1°C. Corals can preserve signals from these events in their calcium carbonate skeletons, precipitated from seawater.
Enterprising scientists devised a new kind of drill, lightweight and modular, that could be carried to any reef and assembled by hand. This was used to drill for proof of ancient climates and this, in turn, enabled scientists to tease out El Niño’s signal from each annual layer of the coral. Besides measuring the strontium signal, researchers compared the carbonate ions’ levels of heavy oxygen, an isotope with two extra neutrons, with their normal “light” oxygen.
Vanatua, where these researchers drilled in the equatorial Pacific was thought to be a dull place. However, sailors long warned of the belt where north-easterly and south-easterly winds collide and rise to create still, humid and unusually warm conditions at the surface.
El Nino and La Nina
In 1957, a strong El Niño struck the Pacific during the International Geophysical Year, when researchers fanned out worldwide to study the planet. In several papers in the mid-1960’s, Jacob Bjerknes, a meteorologist at the University of California, Los Angeles, proposed that the two anomalies were entwined and that they regularly interacted to influence not just the Pacific, but the whole world, through “teleconnections” in the atmosphere. “That was the big bang of El Niño history,” says Michael McPhaden, oceanographer at the National Oceanic and Atmospheric Administration.
At their core, El Niño events occur when the Pacific swings out of balance. Researchers later realized Bjerkne’s feedback could run in reverse; trade winds stir up the eastern Pacific cold water, temperature differences between east and west grow and strengthen the winds and warmth and storms are pushed farther west. They named that pattern La Niña.
With their additions and subtractions to global temperatures, El Niño and La Niña events complicated early efforts to recognize human-driven global warming. That climate signal has long since emerged. But its influence on El Niño remains mysterious. Some researchers see hints of stronger “super” El Niños and multiyear La Niñas in the past 80 years. But most believe temperature records are too short and noisy to discern any trend, says Amy Clement, a climate scientist at the University of Miami. “The null hypothesis is very hard to reject—that it’s all random variability and [El Niño] comes and goes.”
One reason for this confusion is that the atmosphere and the ocean are in a tug-of-war for influence. Many models suggest climate change will cause air over the eastern Pacific to warm faster than in the west, weakening the large-scale air circulation responsible for the trade winds. With weaker winds, strong El Niño events should occur more often.
Wenju Cai, a climate scientist at Australia’s Commonwealth Scientific and Industrial Research Organisation cites another ocean factor, favouring stronger El Niños. However, scientists are optimistic that the models will eventually reveal factors that matter most among the welter of proposed mechanism as many models showing El Niño and La Niña events well are converging, but not all scientists agree.
Half a world away, in Antarctica, other El Niño events could be preserved not in coral, but in ice. Last year, a team led by Christo Buizert, a glaciologist at Oregon State University, showed in the journal Climate of the Past that variations in noble gases contained within microscopic bubbles in ice cores can capture an increase or decrease in storminess in a region.
Antarctic storms may seem a local phenomenon, but the weather in West Antarctica, especially, is closely tied to changes in the Pacific through shifts in the westerly winds. “It really ties Antarctica to the global circulation,” Buizert says. He plans to measure several more ice cores, to better tease out El Niño’s stormy signal. If he and his colleagues can do that, they could uncover a record going back hundreds of thousands of years.
