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Getting Warmer

By Brett Israel

The El Niño Southern Oscillation (ENSO) is Earth’s main source of year-to-year climate variability, but its response to global warming remains highly uncertain.

Scientists see a large amount of variability in the ENSO from climate records going back thousands of years. Without a clear understanding of what caused this variability, predicting the climate phenomenon’s future is difficult. Now, a new study shows how this climate system responds to various pressures such as changes in carbon dioxide and ice cover, in one of the best models used to project future climate change.

“All of the natural climate fluctuations are in this model, and what we see is that the El Niño responds to every single one of these, significantly,” said Kim Cobb, a professor in Georgia Tech’s School of Earth and Atmospheric Sciences.

In the study, researchers analyzed a series of transient coupled general circulation model simulations forced by changes in greenhouse gases, orbital forcing, meltwater discharge, and the ice-sheet history throughout the past 21,000 years. This is the farthest into the past that this model has been run continuously.

The modeling required supercomputers at Oak Ridge National Laboratory and the National Center for Atmospheric Research to be dedicated to the simulation for months.

“The model gives some very clear predictions that are very much in line with some of the best understandings of the physics controlling the El Niño system,” Cobb said. “It shows that this climate system in the model is sensitive to a variety of different natural climate changes that occurred over the past 21,000 years.”

Published in the journal Nature, the study was sponsored by the National Science Foundation and the Department of Energy.

Kim Cobb
Kim Cobb

is a professor in the School of Earth and Atmospheric Sciences.

El Nino

This image shows the peak warming in the tropical Pacific during the last big El Niño event, in the winter of 1997. Credit: NASA

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