Columbia University Ph.D. student Celeste Pallone devotes her research time observing Eastern Equatorial Pacific dwelling planktonic foraminifera –– very tiny creatures that can give huge clues into the pace of ocean climate change.

“Marine sediment cores act as an archive of sea surface temperatures, past environments, including past temperatures, and general environmental factors, such as past global ice volume,” she said of the single-celled, shelled organisms she studies at Columbia’s Lamont-Doherty Earth Observatory high in the Palisades outside New York City. “I examine these proxies, which can be biological or chemical or physical, and then using them I reconstruct oceanographic conditions in the past helping craft record of the El Niño-Southern Oscillation (ENSO).”

Climate change threatens El Niño and other ages-old weather systems with severe disruptions. ENSO varies on 2–7 year timescales and has major influences on temperature, wind patterns, biological productivity and rainfall across the tropical Pacific and far beyond. This also includes crop yields, floods and droughts at multiple locations, said Jerry McManus, field researcher and professor at Columbia’s Department of Earth and Environmental Sciences, and Lamont-Doherty. Understanding the baseline influences on this system is key to gauging how it may be altered through climate changes.

The latest report from the U.N.’s International Panel on Climate Change expresses continued uncertainty about how the El Niño-Southern Oscillation will respond to continued warming, although the consequences that play out in the global water cycle are likely to be greater (more rain and flooding in some areas, with increased drought in others). South American countries such as Peru rely on the periodic El Niño to bring warmer ocean waters and rainfall. The uncertainly over El Niño is unsettling.

Pallone is seeing how she can reconstruct the oceanography of the eastern equatorial Pacific Ocean (the region of the open ocean directly south of Mexico and Central America) during a particularly interesting time in Earth’s past as she reported at the annual Comer Climate Conference, an international gathering hosted in southern Wisconsin but held virtually this fall.

El Niño is an oceanic climate pattern that characterizes unusual warming of surface waters in the eastern tropical Pacific Ocean. Considered the warm phase of a larger phenomenon called the El Niño-Southern Oscillation, the system marks a periodic warming of ocean surface temperatures. Its opposite, La Niña, is marked by an unusual cooling of oceanic surface temperatures. El Niño brings drier warmer weather to the northern United States and wetter conditions to the south.

“If you have a strong El Niño event, that might be followed by a strong La Niña event as well –– but it is a consistent oscillation that we’ve observed,” Pallone said.

El Niño/La Niña’s hydrological effects are the most important implications on the human population. It can affect rainfall patterns impacting agriculture or even flooding and monsoonal seasons. With satellite measurements of sea surface temperature since the 1980s, there are historical records that indicate the same kind of variability that we observe today suggesting that the ENSO system has been occurring for certain at least the past several thousand years, perhaps even more.

“If we can kind of identify periods that had recurrent warming episodes, for example, or a really large range of temperature variability, we can associate those periods with stronger or more frequent El Niño events,” Pallone said.

Pallone’s research is tri-fold. She uses multiple methodologies to reconstruct the surface and subsurface oceanography of the eastern equatorial Pacific Ocean during a particularly interesting time in Earth’s past, according to McManus.

“She makes many measurements of the oxygen isotope ratios in individual specimens of surface-dwelling planktonic foraminifera shells preserved in deep-sea sediments deposited at that time to learn about the temperature each one experienced during its month or so lifetime, and to compare the range of temperatures that characterized different intervals in the past,” he said. “That tells us something about El Niño-Southern Oscillation (ENSO) variability.”

Another piece of her research is an analysis of multiple specimens of foraminifera species that live at a range of depths below the sea surface to assess their shells and biology as a way to assess where and how fast the temperature changes beneath the surface ocean, hallmarks of El Niño and La Niña events.

Ultimately, by combining methods, this enables Pallone to make a richer and more robust reconstruction of the ocean state in the EEP at different times throughout history.

“Because of the global circulation of the atmosphere in the ocean, if you have an event happening in the equatorial Pacific, for example, you’ll have effects in other parts of the world,” Pallone said.

Pallone started her research thinking that by using the foraminifera as a proxy and the MIS5 time period, she could create a good analog for modern warming.

“If we can reconstruct the environment during (MIS5), maybe it will inform about what changes could be coming in the future,” she said. “This, with most comparisons between the paleo record and the modern, we’re going to have kind of changes in temperature that might have been or that might be quicker than anything that we’ve seen in the past. But the past is still a useful analog for what could happen in the system.”

For the future, global efforts are needed to curb climate change. At the 2021 Glasgow Climate Conference, the United Nations called for a worldwide response to accelerate climate action to limit global temperature rise at a 1.5 degree C tipping point. The goal called for cutting global fossil fuel emissions by 45% compared to 2010 levels and doing so by 2030. The goal was not adopted.

Pallone’s research is a small but crucial step in reaching toward this goal.

“El Niño events are the dominant source of like this kind of decades scale climate variability today,” Pallone said. “It’s unsettling that we’re not so confident in what could happen to them in the coming years or in the coming century.”