By Constantino Panagopulos
Special to Rice News
The climate pattern El Niño varies so dramatically on its own accord, scientists will have a hard time detecting whether it gets stronger because of global warming, according to a study by climate scientists at Rice, the University of Texas at Austin and the University of Colorado Boulder.
Trying to get a clearer picture of how climate change may impact El Niño in the future, the researchers analyzed 9,000 years of Earth’s history, drew on climate data contained in ancient corals and ran climate simulations on a UT supercomputer. Their results were published in Science Advances .
“Because the El Niño Southern oscillation has such a profound impact on weather and climate, figuring out whether or not global warming is going to be a big enough knock to change it is going to be a really critical question for the future,” said Rice co-author Sylvia Dee, an assistant professor of Earth, environmental and planetary sciences. “I’m hopeful that this will really be a call to action for the community.”
El Niño is the warm phase of the El Niño Southern Oscillation, a climate phenomenon that starts in the Pacific Ocean sets the stage every few years for weather patterns worldwide. Strong El Niño events, like those in 1997 and 2015 that brought wildfires to the rainforests of Borneo and caused widespread bleaching to the world’s coral reefs, come around about once a decade.
Computer models, however, don’t offer a clear answer to the question of whether El Niño events will become weaker or stronger as the world warms due to climate change.
“Much of the world’s temperature and rainfall is influenced by what happens in the tropical Pacific Ocean,” said study lead author Allison Lawman, who began the research as a graduate student at UT’s Jackson School of Geosciences and continued it during a 16-month postdoctoral fellowship in Dee’s lab.
“The difference in rainfall between greater or fewer strong El Niño events is going to be a critical question for infrastructure and resource planners.” said Lawman, now a postdoctoral researcher at CU Boulder.
To gauge whether a computer model accurately simulates Earth’s future climate, researchers can have the model simulate a period in Earth’s past and compare the model’s output with the physical record of Earth’s climate from that period. One source of physical evidence of Earth’s paleoclimate is coral, whose geochemical properties depend on ocean temperature.
Lawman, Dee and their collaborators used the Lonestar5 supercomputer at UT’s Texas Advanced Computing Center to run a series of climate simulations of a period in Earth's history before humans began influencing climate and the main source of climate change came from a tilt in Earth’s orbit. They verified findings from the simulations using a coral emulator, software Lawman had previously developed to improve the accuracy of model comparisons with climate records from ancient corals.
The researchers found that although the occurrence of strong El Niño events intensified over time, the change was small compared to El Niño’s highly variable nature.
“It’s like trying to listen to soft music next to a jackhammer,” said study coauthor Jud Partin, a research scientist at UT’s Institute for Geophysics.
Dee, Lawman and the study’s other authors call for further investigations into even earlier times in Earth’s history, like the last ice age, to see how El Niño responded to more intense changes in climate forces.
“Scientists need to keep pushing the limits of models and look at geological intervals deeper in time that could offer clues on how sensitive El Niño is to changes in climate,” said co-author Pedro DiNezio, an associate professor at CU Boulder. “Because if there’s another big El Niño it’s going to be very hard to attribute it to a warming climate or to El Niño’s own internal variations.”
The research, including much of Lawman’s doctoral studies, was funded by the National Science Foundation. Project partners included Rice and the University of Arizona.
—Constantino Panagopulos is a science writer at the University of Texas at Austin’s Jackson School of Geosciences