Dramatic variations in the Earth’s main magnetic field during the 20th century

Analysis of the International Geomagnetic Reference Field (IGRF) 1900–2000 shows that the Earth’s main magnetic field has changed dramatically during the 20th century: its dipole moment has decreased by 6.5% since 1900, the strengths of its quadrupole and octupole have increased by 95% and 74%, respectively, four major planetary-scale magnetic anomalies on the Earth’s surface have enhanced by 21%–56%, and the magnetic center has shifted 200 km towards the Pacific Ocean. These time-variation features are similar to the behavior before a geomagnetic polarity reversal.