Statistical simulations of the future 50-year statistics of cold-tongue El Nio and warm-pool El Nio

Recent extensive studies have suggested that the occurrence of warm-pool El Nio has increased since the late 1970s and will increase in future climate. Occurrence frequencies of cold-tongue and warm-pool El Nio have been investigated in the observational record (1980-2006) and in the future 50 years (2007-2056) based on 100 synthetic SST datasets with estimates of statistical confidence. In the observational record, 80% of the warm-pool El Nio occurred since 1980 over a period of 27 years; only 20% of the warm-pool El Nio occurred prior to 1980 over a period of 110 years. The 100 synthetic datasets, on average, produce 142 months of cold-tongue El Nio in 2007-2056 as opposed to an average 107 months in the same length of the observational data; this is a 20.7% increase in the occurrence of cold-tongue El Nio compared with the observational period. Warm-pool El Nio occurred for 112 months in 2007-2056 as opposed to an average occurrence of 42 months in the observational record; this is 2.5 times the occurrence frequency in the 1980-2006 period in the synthetic datasets. As a result, occurrence frequencies of cold-tongue and warm-pool El Nio in the period of 2007-2056 become quite comparable to each other in the synthetic datasets. It is expected in the next 50 years that warm-pool El Nio will be nearly as frequent as cold-tongue El Nio.