Study finds climate change is strengthening El Niños

A new study suggests that El Niños, the natural climatic chaos agents that appear periodically and drive up global temperatures, are becoming stronger because of human-caused climate change.

El Niños are more than 36 per cent stronger than they were before the Industrial Age began in the mid-1800s, with a 16 per cent increase in just the past 40 years suggesting that the trend is accelerating, according to a recent study in the journal Science.

The findings come as a strong El Niño that formed a couple of months ago is forecast to become the most powerful on record in the coming months. El Niños, which involve the temporary warming of parts of the equatorial Pacific, disrupt weather patterns worldwide and increase the likelihood of extreme events, including heatwaves, floods in some places, and droughts in others. They can cause trillions of dollars in damage.

“That’s important because strong El Niños have much stronger impacts on climate hazards and extremes worldwide. When we set out to answer the question of why this might be happening, we set our data up against a record of global temperature, and we found that the increase in El Niño’s strength closely parallels the rise in global temperature that is due to human causes, such as the burning of fossil fuels,” said study lead author Julia Cole, a palaeoclimate scientist at the University of Michigan.

Her study examines El Niños dating back roughly 900 years.

“El Niño is the most violent aspect of climate variability worldwide, with effects ranging from local fisheries collapse to widespread coral die-offs, to severe droughts and food shortages around the world,” said Dalhousie University marine scientist Boris Worm, who was not involved in the study.

Worm quoted the late climate scientist Wallace Broecker, who warned that “the climate system is an angry beast and we are poking it with sticks”. Worm then added: “Human emissions are the stick and El Niño is of the ‘angry’ outbursts that can be so threatening to our collective safety.”

An El Niño’s strength is determined by measuring water temperature in a region of the central Pacific around the equator and comparing a three-month average with normal conditions. If it is 0.5°C (0.9°F) warmer than normal, it becomes an El Niño. The top of the scale is 2°C (3.6°F) and is classified as “very strong”. The most recent weekly El Niño reading stands at 2.7°C (4.9°F) and is expected to continue strengthening for another two to four months, according to Columbia University’s El Niño tracker.

Scientists have long theorised that as the world warms, El Niños would become stronger because they are based on ocean-temperature differences relative to average conditions. But observational records only go back about 75 years, leading scientists to argue that the available data are too limited to establish a clear trend. Researchers have therefore looked for indirect evidence of El Niños rather than relying solely on water-temperature measurements. For example, scientists have examined historical records of weather changes around the world and identified past El Niños, such as the powerful event of 1877, through the effects they produced across the globe.

USING CORAL FOSSILS

Cole’s team took a novel approach by examining coral fossils spanning several centuries, using them as “a time machine to look into the past”, she said.

Cole said measurements of calcium-to-strontium ratios in coral skeletons, together with different oxygen isotopes, provide two independent indicators of the seawater conditions in which the coral formed. Another measurement involving uranium and thorium indicates when the skeletons were formed.

Cole examined 29 coral fossils in the Galapagos Islands: 14 from before the industrial era, 14 from after the modern era began, and one from around the time the industrial era was beginning. The oldest dated to about the year 1100.

The temperatures she derived from the fossils over more than 900 years are incomplete, with significant gaps. But when she charted the data, she said, it resembled a hockey stick, echoing the description used for a landmark 1990s study of historical global temperatures.

She and other scientists say the situation is likely to worsen.

“It raises the spectre of a future where larger El Niño and La Niña events are dialling up the pace and severity of weather and climate extremes,” said Kim Cobb, a coral and climate scientist at Brown University, who was not involved in the study.

SCIENTISTS SPLIT

Scientists outside the study are divided on the findings, with some hailing the research as important and credible, while others remain unconvinced because it appears to conflict with some recent observations.

“Corals are the gold standard for El Niño reconstruction, and this brings a goldmine of new material to the table,” Cobb said. “We can either wait many, many decades for the instrumental record to get long enough to detect a shift in El Niño properties, or we can use centuries of El Niño reconstructions provided by palaeoclimate records. Taken together, the palaeoclimate data that we have from across the Pacific is fairly consistent in pointing to an intensification of El Niño events with global warming.”

Both University of Pennsylvania climate scientist Michael Mann, originator of the temperature hockey-stick graph, and University of North Carolina marine scientist John Bruno said the coral data conflict with recent observations of water temperatures in the Galapagos.

The data show “a substantial decline in recent decades” in El Niño-related variations near the Galapagos during the period when greenhouse gases increased temperatures most rapidly, Mann said.

What is being reflected in the coral record is not necessarily a change in El Niño activity as much as the warming caused by greenhouse gases, Bruno said.

Cole argued that the enormous 1997-98 El Niño, followed by a series of smaller events until 2023-24, created the impression that El Niños were not strengthening because measurements are often based on relatively short periods of around 20 years. She said several years between major El Niño events skewed the data. According to Cole, El Niño varies greatly in intensity, and that natural variability does not disappear simply because the phenomenon is responding to warmer conditions.

But the scientists all agreed on one point: climate change remains a serious problem, regardless of whether El Niño is becoming stronger.

“It’s important to point to this as one more reason why we need to get off fossil fuels,” Cole said. “There isn’t a magic bullet that’s going to slow El Niños down.”

AP