Corals Reveal El Niño Events Have Become Stronger in Recent Decades, Probably Because Humans Have Been Heating Up the Planet

As the world braces for the “super” El Niño currently gathering strength in the Pacific Ocean, scientists have found that the events have been intensifying as the world warms. That’s according to an analysis of records preserved in corals from the Galápagos Islands. It hints that El Niño climate swings have grown stronger since we started burning more fossil fuels—releasing planet-warming carbon dioxide into the air—in the mid-19th century.

While the findings, published in the journal Science on August 27, don’t go as far as blaming human-caused climate change for this trend, they do suggest it is the most likely culprit. It moves between two extremes: El Niño, characterized by warmer-than-average surface water temperatures in the central and eastern tropical Pacific Ocean, and La Niña, defined by cooler-than-average water temperatures in the region. ENSO involves interactions between the atmosphere and the ocean, and it’s a major driver of changes in the global climate.

The El Niño phase, for instance, generally brings wetter and cooler winters to the southern United States, while parts of South America, South Asia and Australia experience hot, dry weather. Last month, the National Weather Service announced that there’s a nearly 70 percent chance the El Niño currently brewing could become the strongest one on record, which dates back to 1950. Because of those far-reaching effects, scientists want to know whether rising global temperatures are affecting ENSO.

However, computer simulations struggle to replicate the delicate dance between the atmosphere and ocean, and reliable preindustrial temperature measurements from some parts of the tropical Pacific are scarce, reports James Dinneen at Nature. These animals offer a precise window into the ocean’s past. Since 2006, she and her colleagues have collected thousands of coral samples from the Galápagos Islands, an area key to El Niño’s formation, per Nature.

The specimens collectively hold a record of the past millennium. Within the corals’ layers, levels of the element strontium and different forms of oxygen can reveal past weather patterns. When ocean waters are warmer, the animals tend to pull less strontium into their skeletons and use more of a lighter version of oxygen, called O16, compared to the heavier O18.

Chemical analyses of these elements in the time capsules revealed that ENSO variability over the past 40 years was about 36 percent greater than that during preindustrial times. The recent swings are also roughly 16 percent greater than those that took place between 1851 and 1982. Some studies have failed to find a strong link between global warming and ENSO variability.