A Climate Change Signal in the Tropical Pacific 

Throughout the world, extreme weather is driving a growing death toll, exacting billions in damage, threatening food and water security and escalating forced migration. Yet some of the most sophisticated climate models—computer simulations of the Earth’s vast, complex climate system, based upon the laws of physics—are missing crucial signals.Now, a research paper published in Nature Communications, co-authored by postdoctoral researcher Feng Jiang; climate scientist Richard Seager, the Palisades Geophysical Institute/Lamont Research Professor at Columbia Climate School’s Lamont-Doherty Earth Observatory and Mark Cane, the G. Unger Vetlesen Professor of Earth and Climate Sciences (retired) holds key findings as to why climate models are getting many things wrong.“Our Lamont work is at the center of the debate in the climate science community and has sparked climate scientists worldwide to rethink their models,” says Seager. “The discrepancy can be found in the tropical Pacific Ocean. Specifically, the equatorial cold tongue,” Seager explains. The cold tongue is a strip of relatively cool water stretching along the equator from Peru into the western Pacific, across a quarter of the Earth’s circumference. It has been bucking predictions by not warming the way generations of climate models say it should.Recurrent and emerging sea surface temperature (SST) trend patterns in the tropical Pacific. Source: Jiang, F., Seager, R. & Cane, M.A. A climate change signal in the tropical Pacific emerges from decadal variability. Nat Commun 15, 8291 (2024).“A cold tongue that is not warming while the rest of the tropical ocean is means drying in southwest North America, East Africa, southeast South America but favors wetting in other regions such as the Amazon,” says Seager. “It also means more tropical cyclones in the Atlantic basin.”  By getting the trends in cold tongue temperatures wrong, climate models will also be getting projections of regional climate change in these and other regions wrong. It’s a discrepancy that’s been noted for more than two decades. Many scientists believed that natural El Niño Southern Oscillations variability was masking the response to rising greenhouse gases and that eventually the equatorial cold tongue would start warming up and line up with the models. That hasn’t happened.“For 27 years this discrepancy between the models and the observations is still there. In fact, it’s gotten bigger over time, not smaller,” says Seager. “It’s beyond time for the models to be improved to better capture the processes that govern the surface temperature response to CO2 in the tropical Pacific.”The study shows—for the first time—that there are two patterns at work, one that is natural variability and oscillates back and forth, the so-called Interdecadal Pacific Oscillation, and one that has been steadily emerging since the mid-1950s, a trend the study calls the Pacific Climate Change (PCC)