Greenhouse warming and internal variability synergistically increase extreme and central Pacific El Niño frequency

Researchers from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences and their collaborators have investigated past changes in El Niño diversity and quantified the contribution of anthropogenic forcing and internal variability to the recently observed El Niño diversity. They found that greenhouse warming and internal variability synergistically increased extreme and Central Pacific El Niño frequency since 1980.

The study was published in Nature Communications on Jan. 24. It is based on multiple pieces of evidence, including multiple long-term observations and the outputs from sixth phases of the Coupled Model Intercomparison Project (CMIP6).

The researchers revealed another extreme El Niño and Central Pacific El Niño epoch around the year 1900, with similar spatial and temporal evolution, dynamic processes, and climate impacts as those that occurred in the last 40 years. They also found that the frequent occurrence of extreme El Niño events and Central Pacific El Niño events since 1980 was caused by the combination of anthropogenic forcing and internal variability associated with the Atlantic Multidecadal Oscillation.

"A positive Atlantic Multidecadal Oscillation enhances the zonal sea surface temperature gradient in the Central Pacific, which strengthens zonal advective feedback, favoring extreme and Central Pacific El Niño development," said Prof. Huang Gang, corresponding author of the study.

Moreover, using a statistical model, the researchers quantified the contribution of anthropogenic forcing and internal variability to the recently observed El Niño diversity.

"How El Niño will change in the future is a crucial issue, yet model projections remain large uncertainty. Understanding the observed variation of El Niño may help more accurately project El Niño's future change," said Prof. Huang.