Fifty-year investigation of the correlation between the geomagnetic field and climate

After 50 years of research on the correlation between the geomagnetic field and climate, we have gained a deeper understanding that the regulation of climate by geomagnetic field changes is far more complex than previously imagined. In this paper, we comprehensively review the research connecting the geomagnetic field and climate over the past 50 years, examining different spatial and temporal scales. Our results demonstrate a significant correlation between geomagnetic field changes and climate at various scales, including millennial-scale geomagnetic reversals, thousand-year-scale geomagnetic shifts, centennial-scale geomagnetic abrupt, and even decadal-scale variations in geomagnetic activity. The Matuyama–Brunhes geomagnetic reversal is associated with the cold climate. The increase in galactic cosmic rays (GCR) during this period gave rise to the formation of low-altitude cloud "umbrella effects", subsequently weakening the East Asian summer monsoon and intensifying the East Asian winter monsoon. Archaeomagnetic data from Mesopotamia remarkably illustrates a consistent correlation between four cold periods in the last three thousand years and a sudden increase in geomagnetic anomalies. Exploring the possibility that these geomagnetic anomalies correspond to extreme tilts of the Earth's dipole, it is hypothesized that auroral ovals and sub-auroral regions may have expanded to lower latitudes. In these regions, cosmic rays potentially interacted with a more humid troposphere, resulting in increased cloud cover and, consequently, observed atmospheric cooling. Changes in GCR flux, induced by solar activity and variations in the geomagnetic field, are proposed to have significant implications for alterations in temperate pressure systems, precipitation patterns, and atmospheric electric fields. These effects play diverse roles within the intricately coupled system of the Earth's atmosphere and the near-Earth space environment. However, it's important to note that correlation does not imply causation, and the potential mechanisms by which the geomagnetic field influences climate change are still a subject of debate. The cosmic ray-cloud mechanism is the most promising avenue for understanding how the geomagnetic field regulates climate, operating effectively across different time scales, but its exact physical mechanisms and relative importance remain unresolved issues. We propose that understanding the correlation between the geomagnetic field and climate from the perspective of solar-terrestrial multisphere coupling is crucial, with a specific focus on the response of regional climate systems to changes in regional magnetic fields. By integrating knowledge from ancient times to the present, from regional to global perspectives, we aim to form a comprehensive understanding of the correlation between the geomagnetic field and climate change. The recent successful launch of Aoke-1, which can delicately characterize magnetic field changes in the South Atlantic Anomaly (SAA), the first discovery of the centennial-scale western Pacific anomaly (WPA), and the rapid development of paleomagnetic/archaeomagnetic and paleoclimate data reconstruction have provided new historical opportunities for research on the geomagnetic field and climate. This progress indicates that the study of the impact of geomagnetic field changes on climate will be propelled to new heights.