Exploring Earth’s Weakening Magnetic Field and What It Means for Our Planet

Scientists have been diligently studying Earth’s magnetic field for a long time. Recent research presents a new model of the magnetic field at the core-mantle boundary for the years 1590 to 1990, called "gufm1" (Jackson et al., 2000). This model is based on a vast compilation of historical observations of the magnetic field, with a significant portion of the data coming from mariners involved in merchant and naval shipping.

To create this model, researchers had to address challenges, such as correcting data for potential mislocations due to inaccurate knowledge of longitude. They also adopted a stochastic model to account for uncorrected positional errors, reflecting the noise in the data based on a Brownian motion model.

The result of this extensive effort is a detailed model parametrized spatially in terms of spherical harmonics and temporally in B-splines, comprising a total of 36,512 parameters. This model has improved the resolution of the core field and represents one of the longest continuous models of the field available.

Secular variation refers to changes in Earth’s magnetic field that occur over extended periods, and these variations have been observed to shift magnetic declination by tens of degrees over hundreds of years. The dipole component of Earth’s magnetic field, which is the primary contributor to its protective properties, has been weakening at a rate of approximately 6.3% per century for the last two centuries.

While this rate might sound concerning, it’s essential to put it into perspective. Even at this rate of decrease, the magnetic field would take about 1,600 years to become negligible. Moreover, this rate is not unusual when considered within the context of the last 7,000 years.

One intriguing aspect of secular variation is the westward drift of the magnetic field, happening at a rate of about 0.2 degrees per year. This drift is not uniform across the globe and has varied over time, with periods of eastward drift in the past.

Earth’s magnetic field isn’t constant; it occasionally undergoes reversals, where the North and South geomagnetic poles switch places. Evidence of these reversals can be found in basalt rocks, sediment cores from the ocean floor, and seafloor magnetic anomalies. These geomagnetic reversals are seemingly random, with intervals ranging from less than 0.1 million years to as much as 50 million years.

Paleomagnetic records, including lava flows and sedimentary deposits, hold the key to understanding the history of these reversals. In some cases, they suggest that the magnetic field may have shifted rapidly, challenging our previous understanding of its behavior.

Recent observations show that the Earth’s magnetic field is weakening, with a significant decline starting in the late 1800s and continuing into the 20th and 21st centuries. This weakening corresponds to a 10-15% decline and has accelerated since 2000 (Witze, 2019). However, it’s crucial to understand that the Earth’s magnetic field is not strictly a dipole field, and fluctuations in its local intensity may not represent the overall trend.

Additionally, the magnetic north pole is drifting from northern Canada towards Siberia at an accelerating rate. This shift underscores the dynamic and ever-changing nature of Earth’s magnetic field.

Earth’s magnetic field is a complex and dynamic phenomenon. While it is gradually weakening, it’s not an immediate cause for concern. The field’s long-term variations are well-documented, and we continue to learn more about its behavior over time. Understanding these changes is essential for scientific research and long-term planning, but it doesn’t fundamentally alter the things that matter most to us in our daily lives. Our well-being, relationships, culture, and our impact on the planet remain our primary concerns, even as the Earth’s magnetic field continues to evolve.

Jackson, A., Jonkers, A. R., & Walker, M. R. (2000). Four centuries of geomagnetic secular variation from historical records. Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 358(1768), 957–990. https://doi.org/10.1098/rsta.2000.0569

Witze, A. (2019). Earth’s magnetic field is acting up and geologists don’t know why. https://www.nature.com/articles/d41586-019-00007-1 .