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Concurrent heat extremes (CHEs) are becoming increasingly common in the mid‐high latitudes across the Northern Hemisphere (NH), underscoring the need to comprehend their spatiotemporal characteristics and underlying causes. Here we reveal a phase‐locking behavior in Wave‐4 pattern, particularly after mid‐1990s, giving rise to a prominent CHE mode akin to heat extreme pattern observed in 2022, which swept most NH regions. Wave‐4 pattern significantly amplifies the likelihood of CHEs in Eastern Europe (∼30%), Northeast Asia (∼25%), and northwestern coast of North America (∼15%), while reducing the likelihood in central North America and northern Central Asia. During 1979–2022, the identified pattern accounted for over 69.7% of the trends in heat extremes over the mid‐high latitudes of the NH, directly exposing approximately 333.5 million people to heat extremes. Observations and simulations indicate that radiation anomalies over Eastern European Plain and West Siberian Plain play pivotal roles as primary forcing sources for Wave‐4 pattern. Plain Language Summary: Researchers have found that concurrent heat extremes are becoming more common in the Northern Hemisphere. This study discovered that a specific weather pattern, called as Wave‐4, became more prominent after the mid‐1990s and is linked to these heat extremes. This pattern increases the probability of heatwave occurrences in Eastern Europe, Northeast Asia, and northwestern coast of North America while decreasing them in central North America and northern Central Asia. Between 1979 and 2022, the identified Wave‐4 pattern contributed to more than two‐thirds of the increase in heat extremes in the northern hemisphere, affecting around 333.5 million people. It is also determined that unusual radiation levels over the Eastern European Plain and West Siberian Plain are significant factors contributing to the Wave‐4 pattern. This information helps us better understand the causes and characteristics of heat extremes in different parts of the world. Key Points: The Phase‐locked Rossby wave‐4 pattern dominates the concurrent heat extremes across the Northern HemisphereThe identified pattern exposed approximately 333.5 million people to heat extremesRadiation anomalies over the Eastern European Plain and West Siberian Plain play pivotal roles as forcing sources of the pattern [ABSTRACT FROM AUTHOR]

Under global warming, extreme high temperatures (EHTs) have become frequent and enhanced around the world. However, we found that the frequency and intensity of EHTs in Central Asia (CA) are decreasing over the last four decades when the effects of climate warming are removed. From 1979 to 2020, an interdecadal shift in CA's EHTs occurred around the mid‐1990s, preceded by high values (1983–1997) and followed by low values (1998–2016). The observational analysis and numerical simulations using National Center for Atmospheric Research Community Atmosphere Model version 5.3 both demonstrate that the phase transition of Atlantic multidecadal oscillation (AMO) has an important influence on this interdecadal shift. During 1998–2016, the AMO was in a positive phase (+AMO), meaning warmer sea surface temperature anomalies (SSTA) in the North Atlantic, which could lift the geopotential height and cause anticyclonic circulations over the basin. Through the cyclonic–anticyclonic circulation alternating teleconnection wave train over Eurasia, the atmospheric system over the North Atlantic could induce cyclonic circulations and reduce the geopotential heights over CA, that is, weaken the high pressure at the upper level, which is not conducive to warming and EHTs in CA. For the −AMO period (1983–1997), due to the similar atmospheric response mechanism, the negative SSTA in the North Atlantic and the wave train with reversed anomaly centres can be found, causing anticyclonic circulations and rising geopotential heights over CA. The high pressure at the upper level in CA would be strengthened, leading to favourable EHT conditions. Overall, we conclude that the current AMO (+AMO) has a mitigating role on the EHTs of CA, and the findings also emphasize that if the future AMO shifts to a negative phase, the EHTs of CA may worsen than at present. [ABSTRACT FROM AUTHOR]