Multi-model statistics associated with the increase in frequency of extreme La Niña events Multi-model ensemble histogram of quadratically detrended outgoing longwave radiation anomalies in the Niño-4 (central Pacific) region. Values are separated into 5 W m-2 bins centred at the tick point for the Control (blue) and Climate Change (red) periods. The multi-model median for the Control (solid blue line) and the Climate Change (solid red line) periods are indicated, and the corresponding values for all La Niña samples only (Niño4 < -0.5 s.d.) are indicated by dashed blue (Control) and dashed red (Climate Change). a, for all samples, i.e. all summer (December, January, February) seasons, and b, for extreme La Niña samples only, respectively. The histograms for all samples between the two periods are not statistically significant (H=0), but statistically significant (H=1) for both the La Niña and the extreme La Niña samples, above the 95% confidence level according to a 2-sided Student t-test. Graphic: Cai, et al., 2015

By Warren Cornwall
26 January 2015 (National Geographic) – People living around the Pacific Ocean, including in parts of Asia, Australia, and western North and South America, should expect wilder climate swings in the 21st century. Extreme versions of El Niño and La Niña, the sibling Pacific weather patterns that can translate into torrential rains or searing droughts, will likely occur nearly twice as often—approximately once every decade—if greenhouse gases continue increasing on their current trajectory, an international team of scientists has concluded. “The results are actually very, very convincing, and terrifying in a way because we know the impact can be dramatic,” said Wenju Cai, a climate scientist who was the lead author of two recent papers about the research, the second of which was released Monday. If the predictions prove true, it could mean tens of thousands more weather-related deaths and devastating economic damages.
The paper published Monday reveals the La Niña side of the equation and appears in the journal Nature Climate Change. Using computer models that simulate how increasing greenhouse gases alter ocean and land temperatures and wind patterns, the study finds that particularly intense La Niñas will occur approximately every 13 years in this century, compared with every 23 years in the past one. And those La Niñas will follow more frequently on the heels of a severe El Niño—which according to the earlier study is to be expected every 10 years rather than every 20. During the most recent extreme La Niña, in the late 1990s, the southwestern United States endured a severe drought, while more than half of Bangladesh was underwater and flooding in China killed thousands and displaced over 200 million people. The preceding El Niño is blamed for weather that did more than $33 billion in damage and claimed 23,000 lives worldwide. (Related: “El Niño/La Niña: Nature’s Vicious Cycle.”) [more]

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