Climate Scientists Identify Cause of Super El Niño Events

Scientists have identified how Climate Destabilization creates Super El Niños. The west-flowing ocean current along the Equator weakens, allowing warmth from from the Pacific to spread toward the Americas. Climate models indicate that increasing temperature weakens this current.

El Niño, warmer than average waters in the Eastern equatorial Pacific – shown in orange on the map, affects weather around the world. Image credit: NOAA Visualization Lab.

El Niño is a large-scale warming of surface water which takes place every 3 – 6 years in the equatorial zone of the central and eastern Pacific Ocean.

Extreme El Niños of 1982 and 1997 differ from the common kind in that sea surface temperatures start warming in the west of the Pacific Basin and spread eastwards.

These unusual El Niños appeared for the first time in the available record sometime after the mid 1970s,” said Dr Agus Santoso from the University of New South Wales, the lead author of the study published in the journal Nature.

Climate scientists have struggled to explain why these events occurred and if the frequency would change in the future.

... researchers found the key to the mystery was the weakening of westward flowing currents along the Equator in the Pacific Ocean.

As these currents weakened and even reversed, it allowed the heat during these unusual El Niño events to spread more easily into the eastern Pacific.

La Niña events didn’t behave in a similar way, because the currents are strong and flow to the west.

The scientists also determined what this could mean for the future frequency of these unusual El Niños.

“Using observations we demonstrated the likely role of the weaker currents in the unusual behavior,” Dr Santoso said.

These currents are well represented in a number of climate models. Using these models we confirmed, even under modest global warming scenarios, these unusual El Niño events doubled in frequency.” [emphasis mine]

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Weakening westward-flowing ocean currents connected to Super El Niños, caused by weakening Westerly winds, are set to get worse. In The Rise and Fall of the Westerlies Matt Owens summarizes recent research on how the Westerlies of both hemispheres are changing rapidly, with serious climate consequences. He says that the Westerlies around Antarctica are moving closer to the South Pole and getting stronger, which poses drought hazard to South America, Australia, New Zealand and South Africa. The Northern Hemisphere Westerlies are weakening and meandering, which may increase drought in North America.

Two circular bands of winds called the westerlies are being changed by human-caused global warming. The consequences from these changes could become quite large and come on suddenly - quite the surprise for anyone who still thinks climate change is a future "slow" problem.

… the austral westerly winds have changed rapidly before, and that regional-scale climate has also rapidly changed as a result.¹ One of the most surprising aspects of his findings is that these significant changes have happened in as little as one year.

The westerlies are associated with the polar jet streams, but unlike the jets, the westerlies reach all the way to the surface of the ground. Westerly winds are found in both hemispheres, and both sets of winds have been changing, although somewhat differently…

Because they reach the ground level (or sea level), they have a significant impact on ocean surface currents as well as the patterns of ocean mixing.

… in just the Antarctic area of the globe, we are … “a steeper thermal gradient in heat from pole to mid-latitudes and resulting stronger zonal (westerly) winds around Antarctica. Strengthened zonal winds help to prevent southward penetration into Antarctica of warmer air. Therefore, despite the dramatic warming of the Antarctic Peninsula and coastal regions of Antarctica, the interior of the ice sheet is not yet feeling the impact of warming. It will once the ozone hole over Antarctica heals.”

… recent research … supports a connection between changes in the westerlies and the decades-long, ongoing Australian drought.

And research … has also connected drought in southern Africa to the westerlies. That research predicts substantially more drought if the westerlies continue to move closer to the pole.⁴

… a paleorecord of the austral westerlies… shows that they can move both abruptly and gradually, and have been doing so at a remarkable pace in recent decades. … they are now “at their maximum southerly extent” of the past 100,000 years. In our conversation, he [Mayewski] said that he expects them to keep pushing further south as global warming continues. This trend is also predicted by a number of global and regional climate models.

… “our investigations point to the likelihood that the drying trend will continue in these regions [southern areas of the Africa, Australia, New Zealand and South America] and to the possibility that there will be in the future abrupt transitions in the continued poleward migration of the westerlies.” This poses numerous serious risks to people, including for example, significant changes in agricultural output, fisheries production, water supplies, and wildfire.

However, on the Northern Hemisphere side of the planet where there isn't nearly as much of a hole in the ozone layer, the westerlies have been weakening.

This is similar to the observed recent pattern of weakening and meandering seen in the Arctic polar jet stream, …

When there's a weakening north-south thermal gradient, the winds (including both the jet stream and the westerlies) move much more like a lazy meandering river … instead of a rapidly-flowing and mostly-straight river …

… the Northern Hemisphere westerlies, while less impressive than the austral set of westerlies, have nevertheless been playing a significant role in the intensity of drought cycles experienced in North America …






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