Chinese researchers have found that greenhouse warming and internal variability have increased the frequency of extreme El Nino and Central Pacific El Nino events since 1980.

The research, conducted by a team of scientists at the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences, was recently published in the journal Nature Communications.

According to the researchers, El Nino has changed its properties since the 1980s, characterized by more common extreme El Nino and Central Pacific El Nino events. However, it had been unclear whether such change is externally forced or part of the natural variability.

The researchers investigated the past changes in El Nino diversity and quantified the contribution of anthropogenic forcing and internal variability to the recently observed El Nino diversity.

They found that the frequency of extreme El Nino and Central Pacific El Nino events also increased during the period 1875-1905 when the anthropogenic carbon dioxide concentration was relatively lower.

They determined that the frequent occurrence of extreme El Nino and Central Pacific El Nino events since 1980 was caused by the combination of anthropogenic forcing and internal variability associated with the Atlantic Multidecadal Oscillation (AMO).

Researchers revealed that a positive AMO enhances the zonal sea surface temperature gradient in the Central Pacific, strengthening zonal advective feedback and favoring extreme and Central Pacific El Nino development.

"Understanding the variation of observed El Nino may help more accurately project El Nino's future change," said Huang Gang, the corresponding author of the study and a researcher at IAP. (Xinhua)