Shifts in El Niño May Be Driving Climates Extremes in Both Hemispheres

The record-breaking heat wave that hit East Antarctica last week, the coldest place on Earth, was a record temperatures surge as much as 85 degrees Fahrenheit above averageThis will bring temperatures near freezing and unexpected surface melting to replace the usual sub-zero conditions.

The heat wave is adding to an ever-growing list of previously “unthinkable” climate events, and puts an exclamation point on an Austral summer that included brutal heat waves and record-high intensity wildfires in Argentina and Chile and flooding caused by record-setting rains in eastern Australia that killed more than 20 people and left thousands homeless.

Other “unthinkable” extremes hit the Northern Hemisphere in the months before that. The December wildfire that erupted in Colorado’s Rocky Mountain foothills changed the perception of fire scientists in that area. In addition, the extreme heat wave in the Pacific Northwest that began in June 2021 was not predicted by climate models. Parts of several German towns were devastated by the flooding rainstorms that intensified global warming as that heat wave receded in July. In recent days, temperatures reached 50 degrees Fahrenheit near the North Pole in Siberia and the Arctic Ocean. 

Scientists exploring possible connections between the remarkable series of extremes in both hemispheres say they are increasingly certain that the powerful El Niño-La Niña cycle in the Pacific Ocean is one of the key links. New research has shown that the cycle has changed in a way that is likely fuel extremes, such as wild swings between heat, drought, and flooding rains.

In the El Niño/Southern Oscillation (ENSO), huge masses of water surge eastward and westward every two to seven years along a vast region of the equatorial Pacific. One of the strongest El Niños on record in 2016 helped boost the average global temperature to a new record high that year.

It’s Happening. It’s happening now

The most recent global science report from the Intergovernmental Panel on Climate Change projected that the global warming fingerprint on the El Niño-La Niña cycle would become apparent after about 2050. However, the destruction of our environment is already evident, according to Wenju Cai (Director of the Center for Southern Hemisphere Oceans Research, Commonwealth Scientific and Industrial Research Organisation, Australia).

Cai was a co-author on a key 2022 study showing that the western Pacific is warming more than the eastern Pacific and that the growing temperature contrast is driving complex changes to the El Niño cycle, but Cai said some key climate signals are emerging, including enhanced rainfall in the areas favored by the respective phases of the cycle. And along with the background global warming, each major El Niño peak since the 1950s has been stronger than the previous, pushing ocean surface temperatures to new highs in the east-central equatorial Pacific, where important climate measurements are made.

“Anything that happens in the tropics affects both the northern and southern hemisphere,” Cai said, adding that, as the El Niño/Southern Oscillation changes, the affected areas are expanding and the extremes are intensifying and lasting longer in both hemispheres.

How global warming changes the El Niño cycle is a “fundamental issue in climate science with critical societal ramifications” because the cycle is so important to driving climate extremes “within and outside the Pacific,” Cai and his co-authors wrote in the study, published in January in Nature Climate Change.

There is not yet a discernible direct link between the current La Niña phase of the cycle and the recent heat wave in the Antarctic: Researchers have not even begun to explore a connection. But the southern polar extreme happened just days after scientists announced the finding that Antarctic sea ice had plummeted to the lowest extent on record, leaving miles of open ocean that’s darker and warmer than a reflective ice shield. And recent research suggests that the El Niño cycle affects Antarctic ice shelves, with more melting from below in their floating sections, but also with increased snowfall on the surface that can thicken the ice.

The warm air flowing from Australia to East Antarctica also dumped record amounts of rain and snowAccording to University of Liege Polar researcher, 65 gigatons of new mass was added to the ice sheet in just three days (March 16, 17 and 18). Xavier Fettweis. 

“Usually, the climate of Antarctica is too cold to have significant accumulation of snow, and most of liquid water from melt or rainfall is absorbed by the snowpack and refreezes,” he said. Under very warm and wet air mass that moved over Antarctica “the ice sheet gained 69 gigatons in three days, three times the usual surface mass gain rate.”

Faster than Expected Again

During the El Niño phase of the cycle, warmer than average water sloshes toward the eastern equatorial Pacific, often spurring intense winter precipitation along the West Coast of North America and North America, with relatively cooler water in the eastern Pacific—conditions that contributed to the 2019-2020 Black Summer fires in Australia.

When the cycle flips to La Niña, as in the last couple of years, the eastern and central equatorial Pacific cool, and parts of the eastern Pacific, known as the ocean warm pool, heats up even more, with broad climate patterns favoring extremes like Australia’s March floods and drought in the southwestern United States.

The oceans contain 93 percent heat trapped by greenhouse gases. The tropical Pacific is the largest tank for this heat. The El Niño-La Niña cycle is the pump distributing that energy, as heat and moisture, to the global climate system, to the east and west of the equator, as well as the north and south. 

Matt England, who studies climate extremes at the University of New South Wales, said that even a decade ago he would not have expected to see impacts from the intensification of La Niña—like the March flooding in Australia—to show up so soon. But it’s not surprising that the effects are being felt in both hemispheres, he said.

“The ENSO cycle definitely involves large-scale reorganization of the global atmosphere, across both hemispheres, north and south, but also east and west,” England said, “It is one of the primary drivers of these climate extremes we’ve been seeing, the classic signature being floods and drought and fire,” shifting between the Americas and Indonesia, Australia and other western Pacific nations, depending on the phase of the cycle,” he added.

The north-south influence of a changing El Niño/Southern Oscillation cycle is harder to see, he said, “because ENSO is mainly about pushing water back-and-forth in an east and west sense along the tropical Pacific.” 

ENSO, along with the east-west shifts in the oceans, also generates large areas of convective moist. These air masses shift around almost like bubbles in an lava lamp. They’re big enough to push around wind belts that carry seasonal rain and snow storms and warm and moist enough to give those storms an extra kick, he said.  

In one example of how the effects ripple globally in both hemispheres, the United States Agency for International Development (USAID), an independent U.S. government agency that delivers international aid, reported last month that La Niña and climate change are causing exceptional drought in East Africa, 

England stated that the Antarctic sea ice effect is complex and that there are very few long-term climate records from this remote area. But it appears that La Niña phases lead to a lower extent of sea ice. Stronger La Niñas could mean more years of record-low Antarctic sea ice, and every time that happens, the ocean warms a bit more, making it harder for the sea ice to form again the following winter, he added.

His advice? Keep your cool for the climate roller coaster ahead.

“Earth’s climate has ways of reorganizing itself in rapid and highly nonlinear ways and El Niño is part of that,” he said. “What concerns climate scientists is that these are not always small and gradual shifts.”