The Circum-global Teleconnection Pattern (CGT) is a key mode of atmospheric variability during boreal summer, characterized by an upper-tropospheric wave train propagating along the subtropical jet. As one of the critical drivers of heatwaves in the Northern Hemisphere's mid-latitudes, how the CGT's structure responds to global warming—and its subsequent impact on future heatwave characteristics—remains inconclusive.

To address this knowledge gap, researchers from the Institute of Atmospheric Physics of the Chinese Academy of Sciences have conducted a study revealing the robust weakening of the CGT under global warming and elucidating its effects on regional heatwaves. Their findings were recently published in Geophysical Research Letters.

Using 34 climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), the research team found that the amplitude of the CGT wave train will decline significantly under a high-emission future scenario, dropping to just 68% of its current magnitude by the end of the century. This uniform reduction in amplitude is reflected in diminished wind anomalies spanning Eurasia to the North Pacific.

To explore the underlying mechanism, the team conducted Rossby Wave Source (RWS) diagnostics. Results indicate that atmospheric circulation anomalies over the eastern Mediterranean will weaken substantially under global warming. Acting as an upstream signal, these weakened anomalies will affect downstream regions across Eurasia, ultimately leading to the reduced CGT amplitude.

Regarding the implications of a weakened CGT for mid-latitude heatwaves, the researchers identified distinct regional shifts: heatwave duration linked to the CGT will increase from 5.5 days to 7.0 days across Eastern Europe, the Qinghai-Tibet Plateau, Northeast Asia, and North America. In contrast, duration will decrease markedly from 9.2 days to 7.5 days over the Middle East. These regional shifts in heatwave duration are driven by changes in upper-atmospheric circulation associated with the weakened CGT.

"This study uncovers the robust changes in CGT structure under global warming," said Prof. ZHOU Tianjun, corresponding author of the study. "We also highlight its impact on shifts in heatwave events worldwide, as well as the potential threats to crop yields and ecosystems."

By clarifying the key role of the Mediterranean circulation in the CGT's weakening, this study provides new evidence for how changing atmospheric variability modes influence heatwave characteristics under global warming.