The El Nino phenomena is among the most fascinating yet least understood topics of climate science.
Every few years a wave of heat and surface pressure changes sweeps across regions of the Pacific. It lasts nine months to two years and has a worldwide effect.
Some believe that the frequency of El Ninos is changing as a result of climate change. I have recently heard it said many times that it is the increased frequency of El Nino and the associated La Nina that has resulted in the flatness of the global annual average temperature in the past decade or so. If true it’s an important observation.
Trenberth and Hoar in 1996 said there is a tendency for more frequent El Nino and fewer La Nina since the late 1970’s which they think is linked to decadal changes throughout the Pacific basin due to global warming. They note a non-El Nino warming between 1990-95 “connected to” the El Nino, which they say is unprecedented in the previous 113 years, and suggest it is linked to increases in greenhouse gasses.