Dr Georgy Falster explaining the Pacific Walker Circulation. Photo and video content available here: Pacific Walker Circulation Media Pack

Researchers have found the atmospheric flow around the Pacific Ocean (the Pacific Walker Circulation) has changed, with important implications for El Niño and La Niña events.

Key findings:

  • The length of time for the Pacific Walker Circulation to switch between El Niño-like and La Niña-like phases has slowed over the industrial era.
  • Multi-year El Niño and La Niña events may become more common as a result.
  • Multi-year El Niño and La Niña events can exacerbate the associated risks of drought, fire, rains and floods.
  • Aerosol pollution (as distinct from greenhouse gases) may impact the strength of the Pacific Walker Circulation, making La Niña events more likely.
  • Volcanic eruptions cause an El Niño-like weakening of the Pacific Walker Circulation.

“After Australia saw severe flooding and rainfall from a rare 3 year La Niña event, our research has found that one of the key drivers of these events is changing, with slower transitions between La Niña and El Niño events” says Dr Georgy Falster, Research Fellow at the ARC Centre of Excellence for Climate Extremes. 

“That means in future we could see more of these multi-year La Niña or El Niño events as the atmospheric flow above the Pacific Ocean switches more slowly between La Niña and El Niño phases” says Dr Falster.

The research, published today in Nature, used global data from ice cores, trees, lakes, corals and caves to build a picture of how the Pacific Walker Circulation has changed over time. Dr Falster began this research whilst working as a Postdoctoral Research Associate at Washington University in St. Louis.

“The Pacific Ocean is one of the most important aspects of global climate and weather – largely due to its size. What happens in such a huge ocean has wide ranging impacts all across the globe” says Dr Falster.

“If atmospheric circulation over the Pacific Ocean changes, known as the Pacific Walker Circulation, that has major impacts on the weather we experience across the entire planet. Human-caused changes to the Pacific Walker Circulation could mean we experience El Niño and La Niña, and the risks associated with them, for longer periods. Multiple years of El Niño and La Niña could become more common”

The researchers say humans are impacting climate systems like the Pacific Walker Circulation, but not in the ways they expected.

“We set out to find out whether greenhouse gases had affected the Pacific Walker Circulation. We found that the overall strength hasn’t changed yet, but instead, the year-to-year behaviour is different” says Dr Falster.

“Ultimately, we know the planet is warming and that warming is caused by human induced greenhouse gases. To plan and adapt for the impacts of climate change, we need to improve our knowledge of climate systems across the board. We need to know how the Pacific Walker Circulation is responding to global warming so we can help communities prepare for potential periods of flood, drought, rain and fire.”

The paper is published today in Nature.  This research was funded by the US National Science Foundation and the Australian Research Council Centre of Excellence for Climate Extremes.

Media contact: Jonathan Brown, jb.brown@unsw.edu.au, 0491 008 719

Editor’s notes:

Video and photographic content is available for use here: Pacific Walker Circulation Media Pack

A separate media release detailing more information about Dr Georgy Falster is available here: Pacific Walker Circulation Media Pack

Embeddable Youtube videos are available here:

What is the Pacific Walker Circulation? https://youtu.be/ydMP4kG3SXs

Research paper explainer: https://youtu.be/EGyEulSGTMQ

Meet Dr Georgy Falster: https://youtu.be/0ltLDQE65hE

University of Hawai‘i at Mānoa comments:

“The tropical Pacific has an outsized influence on global climate and understanding how it responds to volcanic eruptions, anthropogenic aerosols, and greenhouse gas emissions is fundamental to being able to confidently predict climate variability and project future climate in Hawaiʻi and around the globe,” said Sloan Coats, study co-author and assistant professor of Earth Sciences in the University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology. 

“Our study provides a long-term context for a fundamental component of the atmosphere-ocean system in the tropics,” said Coats, whose expertise is Common Era paleoclimate, which focuses on climate variability over the last 2,000 years, and how and why the tropical Pacific is changing with climate change.

“Understanding how the Pacific Walker Circulation is affected by climate change will enable communities across the Pacific and beyond to better prepare for the challenges they may face in the coming decades.”

Bronwen Konecky at Washington University in St. Louis comments:

“What happens in the tropical Pacific doesn’t stay in the tropical Pacific…It impacts vast stretches of the world. The Pacific Walker Circulation is a major driver of variability in global precipitation.”

“There’s incredibly high model agreement, when it comes to future changes in temperature. There is a whole lot less agreement when it comes to future changes in rainfall.”

“We have long known that large volcanic eruptions, especially from the tropics, tend to cool the planet off for a few years. But when it comes to hydroclimate, the impacts are harder to figure out, because rainfall and other hydroclimate variables are so much noisier than temperature. So, it’s just hard to tell: was it a little bit wetter this year because a volcano erupted near Fiji, or for some other reason?”  

“Using our proxy data, we’ve now reconstructed the Pacific Walker Circulation now going back to the year 1200. A major problem we faced was choosing the best statistical technique to build out the reconstructions. So we decided, why pick just one? Instead, we used as many as we could. We’ve calibrated these reconstructions using modern datasets of atmospheric pressure at sea level. By using multiple approaches, we know that our results are robust beyond the error bars of just one statistical tool.”

“What we have found is that following a volcanic eruption, we see a very consistent weakening of the Pacific Walker Circulation.”

What is the Pacific Walker Circulation?

Article and video explainer: https://climateextremes.org.au/what-is-the-pacific-walker-circulation/ 

The El Niño Southern Oscillation (or ENSO) is a climate pattern where the Pacific Ocean and atmosphere above it talk to each other. ENSO affects weather all over the world, and has a big impact on weather in Australia.

The atmospheric part of ENSO has its own name – the Pacific Walker Circulation.

How was this research conducted?

Dr Georgy Falster and her international collaborators used data from ice cores, trees, lakes, corals, and caves that gives us information about the climate over hundreds of years. This was used to compare the Pacific Walker Circulation before the human-caused rise in greenhouse gases and after.