From Tallbloke’s Talkshop

August 25, 2023 by oldbrew

The paper this article is based on informs us that ‘The Pacific Walker circulation (PWC) has an outsized influence on weather and climate worldwide. Yet the PWC response to external forcings is unclear’. Under a headline saying: ‘Greenhouse gases are changing air flow over the Pacific Ocean, raising Australia’s risks of extreme weather’, the article here offers almost nothing to support an argument for any human-caused climate effects ‘in the industrial era’. The paper is somewhat embarrassing for climate models: ‘Most climate models predict that the PWC will ultimately weaken in response to global warming. However, the PWC strengthened from 1992 to 2011, suggesting a significant role for anthropogenic and/or volcanic aerosol forcing, or internal variability’. So that role could be anything or nothing, but the models trended the wrong way anyway. The search for ‘anthropogenic fingerprints’ continues.
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After a rare three-year La Niña event brought heavy rain and flooding to eastern Australia in 2020-22, we’re now bracing for the heat and drought of El Niño at the opposite end of the spectrum, says The Conversation (via Phys.org).

But while the World Meteorological Organization has declared an El Niño event is underway, Australia’s Bureau of Meteorology is yet to make a similar declaration. Instead, the Bureau remains on “El Niño alert.”

The reason for this discrepancy is what’s called the Pacific Walker Circulation. The pattern and strength of air flows over the Pacific Ocean, combined with sea surface temperatures, determines whether Australia experiences El Niño or La Niña events.

In our new research, published in the journal Nature, we asked whether the buildup of greenhouse gases in the atmosphere had affected the Walker Circulation. We found the overall strength hasn’t changed yet, but instead, the year-to-year behavior is different.

Switching between El Niño and La Niña conditions has slowed over the industrial era. That means in the future we could see more of these multi-year La Niña or El Niño type events. So we need to prepare for greater risks of floods, drought and fire. [Talkshop comment – alarmist psychobabble].

An ocean-atmosphere climate system

La Niña and its counterpart El Niño are the two extremes of the El Niño Southern Oscillation—a coupled ocean-atmosphere system that plays a major role in global climate variability.

The Walker Circulation is the atmospheric part. Air rises over the Indo-Pacific Warm Pool (a region of the ocean that stays warm year-round) and flows eastward high in the atmosphere. Then it sinks back to the surface over the eastern equatorial Pacific and flows back to the west along the surface, forming the Pacific trade winds. In short, it loops in an east-west direction across the equatorial Pacific Ocean.

But the Walker Circulation doesn’t always flow with the same intensity—sometimes it is stronger, and sometimes it is weaker.

So far, the Walker Circulation is what’s missing from the current El Niño event developing in the Pacific Ocean: it has not weakened enough for the Bureau to declare an El Niño event.

What’s happening to the Walker Circulation?

The Walker Circulation is a major influence on weather and climate in many places around the world, not just Australia.

A stronger-than-usual Walker Circulation even contributed to the “global warming slowdown” of the early 2000s. This is because a stronger Walker Circulation is often associated with slightly cooler global temperature.

So we need to know how it is going to behave in the future. To do that, we first need to know if—and if so, how—the Walker Circulation’s behavior has changed due to human activities. And to do that, we need information about how the Walker Circulation behaved before humans started affecting the climate system. [Talkshop comment – unsupported assertion].

We reconstructed Walker Circulation variability over the past millennium. We used global data from ice cores, trees, lakes, corals and caves to build a picture of how the Walker Circulation changed over time.

We found that on average, there has not yet been any industrial-era change in the strength of the Walker Circulation.

This was surprising, because computer simulations of Earth’s climate generally suggest global warming will ultimately cause a weaker, or

more El Niño-like, Walker Circulation.

Full article here..
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Research paper: Forced changes in the Pacific Walker circulation over the past millennium (Aug. 2023)