Extreme La Nina events expected to increase

Extreme La Nina events which impact both sides of the Pacific Ocean are predicted to occur almost twice as often, reports a paper published online this week in Nature Climate Change. The atmospheric circulation associated with La Nina generates extreme weather in many parts of the world, including droughts in the southwestern United States, floods in the western Pacific and increased landfalling west Pacific cyclones and Atlantic hurricanes.

El Nino and La Nina events are opposite phases of the natural climate phenomenon, the El Nino/Southern Oscillation. Extreme La Nina events occur when cold sea surface temperatures in the central Pacific Ocean contrast with the warming land areas of Maritime Southeast Asia in the west and create a strong temperature gradient.

Wenju Cai and colleagues report that increased land warming relative to the ocean and an increased frequency of extreme El Nino events, are setting the scene for these events every 13 years compared with a past frequency of one every 23 years. They use a collection of global climate models, selected for their ability to simulate extreme La Nina events, to investigate how the frequency of those events will change with global warming. The authors find that extreme La Nina events will increase in frequency and that approximately 75% of this increase will occur immediately following an extreme El Nino event. The implication of this is that weather patterns will switch between extremes of wet and dry.

In an accompanying News and Views, Antonietta Capotondi notes that “events associated with devastating impacts on the world climate and economies will become more frequent, but they may shortly follow other devastating effects of somewhat opposite sign.” She concludes that “the possibility of more frequent devastating La Nina events must be seriously considered as we prepare to face the consequences of global warming”.

doi: 10.1038/nclimate2509

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