The “hole” in the Earth’s magnetic field over the South Atlantic does not seem to portend an imminent magnetic reversal. That is the conclusion reached by a research group led by Andreas Nilsson, from Lund University, based on a new model that simulates the evolution of the Earth’s magnetic field over the last 9,000 years.
In an article published in Proceedings of the National Academy of Sciences, the team explains that from time to time areas appear where the magnetic field is unusually weak, as occurs in the South Atlantic Anomaly. And the most recent of those “depressions” was generated about 2600 years ago.
The model has been developed from measurements of archaeological finds, marine sediments and volcanic deposits that provide data on the orientation and intensity of the magnetic field in different places and times in the past. The results indicate that the strong regional anomalies are related to recurrent fluctuations in the dipole moment of the magnetic field. Therefore, the Earth’s magnetic field should soon recover both its intensity and its symmetry, with which the “hole” in the South Atlantic could disappear in the coming centuries.
The key is to figure out how unusual the current behavior of the magnetic field is and whether it could herald a drastic change. The geomagnetic field has been weakening markedly for about 200 years, and since the late 1990s the North Pole has been moving about 50 kilometers a year, three times faster than before. Some experts interpreted this change, together with the existence of a region with a very weak field over the South Atlantic, as a sign of an imminent reversal of the polarity of the magnetic field.
The magnetic poles have often reversed in Earth’s history. And such an investment could have serious consequences for humanity. It is likely that the magnetic field almost completely disappeared for centuries, which would have a considerable impact on the Earth’s climate. It would also cause technological problems: satellites, for example, would be exposed to the solar wind.
However, the pole reversal hypothesis is highly controversial, since we do not fully understand the behavior of the magnetic field. Deducing its evolution in short periods of time from sample measurements is extremely difficult. Therefore, Nilsson’s team used a statistical method to reduce the uncertainty associated with the data and thus obtain a coherent global model. The analysis revealed evidence that the magnetic field fluctuates, on time scales of thousands of years, between fairly symmetrical states with a marked dipolar character and others with less pronounced dipolar behavior and large asymmetries, such as the South Atlantic Anomaly.
Consequently, the current configuration of the Earth’s magnetic field would respond to a relatively typical and recurring pattern. Similar variations have occurred on a regular basis over the last 9,000 years, as the strength of the magnetic field exhibits notable oscillations both globally and locally. Therefore, according to the team, an imminent reversal of the poles cannot be expected.
The magnetic field is likely to become more symmetrical in the coming centuries and the South Atlantic Anomaly will disappear. The conclusions of the study are consistent with the results of other research carried out in this field, which has also shown that the Earth’s magnetic field is highly variable and that its current behavior would not herald any imminent drastic change.
Reference: “Recurrent ancient geomagnetic field anomalies shed light on future evolution of the South Atlantic Anomaly». Andreas Nilsson et al. in Proceedings of the National Academy of Sciences, vol. 119, art. e2200749119, June 6, 2022.
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