More extreme El Niño and La Niña events?

Charles Q. Choi in Our Amazing Planet: Ancient trees reveal that the El Niño and La Niña events that wreak havoc on climate worldwide have been even more extreme than anyone knew, a revelation that suggests wilder swings in the future as the world gets warmer. El Niño and La Niña are the warm and cold phases, respectively, of the pattern known as the El Niño Southern Oscillation (ENSO) in the eastern half of the tropical Pacific.

…The scientists analyzed the North American Drought Atlas, which has data from centuries-old trees to deduce the history of drought in North America, particularly the southwestern United States. They used this data to reconstruct the intensity of El Niño and La Niña events over the past 1,100 years.

During El Niño, the unusually warm surface temperatures in the eastern Pacific lead to changes in atmospheric circulation, causing unusually wetter winters in the southwestern United States and thus wider tree rings (representing more growth of the tree). Unusually cold eastern Pacific temperatures during La Niña lead to drought, less growth and narrower rings.

The team's findings agreed well with sea surface temperature records that scientists had already collected in the tropical Pacific over the course of 150 years. They also closely matched data on ENSO captured in both living corals and ones that lived centuries ago around the Palmyra Atoll in the central Pacific. This suggests the tree ring data reflect how ENSO has behaved for the past millennium.

…The tree rings reveal that over the centuries, the intensity of this climate pattern has been highly variable, with decades of strong El Niño and La Niña events and decades of little activity. The least variability happened during the Medieval Climate Anomaly in the 11th century, whereas the highest variability occured between the 18th and 20th centuries.

…Given the current phase of global warming, which is causing temperatures in the tropical Pacific to rise, the world might see "enhanced ENSO variability — more severe El Niños and La Niñas, and more extreme climate conditions around the globe..."

Tree rings, shot by Arpingstone