Increased El Nino frequency in a climate model forced by future greenhouse warming

The El Nino/Southern Oscillation (ENSO) phenomenon is the strongest natural interannual climate fluctuation(1). ENSO originates in the tropical Pacific Ocean and has large effects on the ecology of the region, but it also influences the entire global climate system and affects the societies and economies of many countries(2). ENSO can be understood as an irregular low-frequency oscillation between a warm (El Nino) and a cold (La Nina) state, The strong EI Ninos of 1982/1983 and 1997/1998, along with the more frequent occurrences of El Ninos during the past few decades, raise the question of whether human-induced 'greenhouse' warming affects, or will affect, ENSO3, Several global climate models have been applied to transient greenhouse-gas-induced warming simulations to address this question(4-6) but the results have been debated owing to the inability Of the models to fully simulate ENSO (because of their coarse equatorial resolution)(7), Here we present results from a global climate model with sufficient resolution in the tropics to adequately represent the narrow equatorial upwelling and low-frequency waves. When the model is forced by a realistic future scenario of increasing greenhouse-gas concentrations, more frequent El Nino-like conditions and stronger cold events in the tropical Pacific Ocean result.