Research finds northern hemisphere Rossby waves have shifted one-half wavelength since the late 1970s.

Walker circulation [credit: PAR @ Wikipedia

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We’re told ‘a key global climate connection has shifted since the late 1970s’. (Something like this has previously been called The 76/77 climate shift, or similar.) The wavelength shift couldn’t be simulated on climate models ‘with the known’ [sic] ‘anthropogenic forcings’, leaving researchers ‘suggesting that they are driven by natural variability’ and claiming ‘an essential role of the El Niño-Southern Oscillation (ENSO) behind this change.’ So in a nutshell a key feature of Earth’s climate changed, but with no link found to any human activities. Which begs the question: what happened?
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Heat waves have gotten hotter in the Northern Hemisphere in recent decades, says Phys.org.

Home to about 90% of the world’s population, with the largest fraction living in the mid-latitudes, more frequent and more severe heat waves and droughts have occurred in the Northern Hemisphere—in Europe in 2003, 2010 and 2019, in North America during 2018 and 2021 [Talkshop comment – more severe than the mid-1930s?], and in eastern China in 2013 and 2022.

Given the large causalities and economic losses, it’s been frustrating that predicting these events with global computer models is more difficult outside the Earth’s tropical zone than within it.

Now, scientists from China have shown that a key global climate connection has shifted since the late 1970s, with the most severe heat wave and drought impacts over eastern Europe, eastern Asia and southwestern North America. Their work has been published in Nature Communications.

Both empirical observations and modeling evidence show an essential role of the El Niño-Southern Oscillation (ENSO) behind this change.

Before the late 1970s, ENSO indirectly affected the boreal summer circumglobal teleconnection in a way that modulated the Indian summer monsoon. That link weakened starting in the 1980s, with the ENSO forcing displaced westward, causing a shift of the previous centers of the GCT.
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ENSO patterns, which have been shown to be unpredictable, have a significant effect on climate in the tropics, rainfall, and crop production. Through “teleconnections” they can influence distant parts of the globe as well, often thousands of kilometers away.

One is the boreal summer (June to August) circumglobal teleconnection (CGT) discovered in 2005, an upper-tropospheric atmospheric circulation anomaly that occurs during the Northern Hemisphere summer.

Using reanalysis data—datasets of past weather and climate observations—fed into climate models, it was found the CGT’s structure and variability changed after the late 1970s, along with another global scale, the western North Pacific–North American teleconnection. But back then it could only be roughly predicted about a month in advance.

The CGT consists of Rossby waves—inertial waves present in a rotating fluid—in the upper atmosphere, with 5 wavenumbers in total associated with the Northern Hemisphere jet stream flowing west to east.

The research team from China, with lead author Shankai Tang from Sun Yat-Sen University and Guangdong Laboratory in Zhuhai, China, seven co-authors in China and one at the University of Hawaii at Manoa, has discovered that the northern hemisphere Rossby waves have shifted one-half wavelength since the late 1970s.

Utilizing rainfall data compiled from the National Oceanic and Atmospheric Administration’s Precipitation Reconstruction, and global wind, rainfall, surface temperature and global geopotential height provided by the European Center for Medium-Range Weather Forecasts Reanalysis 5 (ERA5), and sea surface temperatures and a precipitation-evapotranspiration from still other databases, they used the Community Earth System Model version 2 from the National Center for Atmospheric Research (NCAR) to do numerical experiments to examine the CGT for statistical evidence of any changes.

Why the half-wavelength change? One obvious possibility is manmade climate change, but they found that the change discovered could not be simulated using 24 state-of-the-art climate models from the Coupled Model Intercomparison Project Phase 6 with the known anthropogenic forcings, “suggesting that they are driven by natural variability” they write.

Looking at anomalous summertime ENSO years, they found the structure of the summertime ENSO had experienced a significant change over multiple decades, with the sea surface temperatures shifting westward from the equatorial eastern Pacific Ocean and the Chilean coast to the equatorial central Pacific. (The change was found to be the same for both El Niños and La Niñas.)

The descending motion of the Walker Circulation led to suppressed convection and rainfall over the tropical western North Pacific. Through a chain of atmospheric interactions, the result is the half-wavelength western shift of the North Pacific center of the CGT, “and other centers downstream.”

Full article here.
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Image: Walker circulation [credit: PAR @ Wikipedia]

Source: https://tallbloke.wordpress.com/2025/03/01/research-finds-northern-hemisphere-rossby-waves-have-shifted-one-half-wavelength-since-the-late-1970s/