Whither ENSO?

Computer model simulations have historically given rise to three climate-alarmist contentions regarding the influence of global warming on El Niño/Southern Oscillation or ENSO events: (1) global warming will increase the frequency of ENSO events, (2) global warming will increase the intensity of ENSO events, and (3) weather-related disasters will be exacerbated under El Niño conditions. The validity of these assertions was the topic of interest in a review article by Vecchi and Witenberg (2010), who stated that it is "of great interest to understand the character of past and future ENSO variations."

In doing so, the two researchers at the US National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory report that "the amplitude and character of ENSO have been observed to exhibit substantial variations on timescales of decades to centuries," and they say that "many of these changes over the past millennium resemble those that arise from internally generated climate variations in an unforced climate model." In addition, they write that "ENSO activity and characteristics have been found to depend on the state of the tropical Pacific climate system, which is expected to change in the 21st century in response to changes in radiative forcing and internal climate variability." However, they indicate that "the extent and character of the response of ENSO to increases in greenhouse gases are still a topic of considerable research," and they state that "given the results published to date, we cannot yet rule out possibilities of an increase, decrease, or no change in ENSO activity arising from increases in CO₂."

Vecchi and Witenberg conclude their review of the subject by stating "we expect the climate system to keep exhibiting large-scale internal variations," but adding that "the ENSO variations we see in decades to come may be different than those seen in recent decades," and admitting that "we are not currently at a state to confidently project what those changes will be."