John AbrahamWed 29 Aug 2018 11.00 BST
A new study finds that weather associated with El Niño events is becoming more severe
As humans put more and more heat-trapping gases into the atmosphere, the Earth warms. And the warming is causing changes that might surprise us. Not only is the warming causing long-term trends in heat, sea level rise, ice loss, etc.; it’s also making our weather more variable. It’s making otherwise natural cycles of weather more powerful.
Perhaps the most important natural fluctuation in the Earth’s climate is the El Niño process. El Niño refers to a short-term period of warm ocean surface temperatures in the tropical Pacific, basically stretching from South America towards Australia. When an El Niño happens, that region is warmer than usual. If the counterpart La Niña occurs, the region is colder than usual. Often times, neither an El Niño or La Niña is present and the waters are a normal temperature. This would be called a “neutral” state.
The ocean waters switch back and forth between El Niño and La Niña every few years. Not regularly, like a pendulum, but there is a pattern of oscillation. And regardless of which part of the cycle we are in (El Niño or La Niña), there are consequences for weather around the world. For instance, during an El Niño, we typically see cooler and wetter weather in the southern United States while it is hotter and drier in South America and Australia.
It’s really important to be able to predict El Niño/La Niña cycles in advance. It’s also important to be able to understand how these cycles will change in a warming planet. Fortunately, a study just published in Geophysical Research Letters helps answer that question. The authors include Dr. John Fasullo from the National Center for Atmospheric Research and his colleagues.
El Niño cycles have been known for a long time. Their influence around the world has also been known for almost 100 years. It was in the 1920s that the impact of El Niño on places as far away as the Indian Ocean were identified. Having observed the effects of El Niño for a century, scientists had the perspective to understand something might be changing.
For example, in 2009–2010, intense drought and heat waves gripped the Amazon region – far greater than expected based on the moderate El Niño at the time. In addition, from 2010 to 2011, severe drought and heat waves hit the southern USA, coinciding with a La Niña event. Other extreme weather in the US, Australia, Central and Southern America, and Asia stronger than would be expected from El Niño’s historical behavior have raised concerns that our El Niño weather may be becoming “supercharged.”