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We study predictions of reversals of Earth's axial magnetic dipole field thatare based solely on the dipole's intensity. The prediction strategy is,roughly, that once the dipole intensity drops below a threshold, then the fieldwill continue to decrease and a reversal (or a major excursion) will occur. Wefirst present a rigorous definition of an intensity threshold-based predictionstrategy and then describe a mathematical and numerical framework toinvestigate its validity and robustness in view of the data being limited. Weapply threshold-based predictions to a hierarchy of numerical models, rangingfrom simple scalar models to 3D geodynamos. We find that the skill ofthreshold-based predictions varies across the model hierarchy. The differencesin skill can be explained by differences in how reversals occur: if the fielddecreases towards a reversal slowly (in a sense made precise in this paper),the skill is high, and if the field decreases quickly, the skill is low. Such aproperty could be used as an additional criterion to identify which modelsqualify as Earth-like. Applying threshold-based predictions to Virtual AxialDipole Moment (VADM) paleomagnetic reconstructions (PADM2M and Sint-2000)covering the last two million years, reveals a moderate skill ofthreshold-based predictions for Earth's dynamo. Besides all of theirlimitations, threshold-based predictions suggest that no reversal is to beexpected within the next 10 kyr. Most importantly, however, we show thatconsidering an intensity threshold for identifying upcoming reversals isintrinsically limited by the dynamic behavior of Earth's magnetic field.

Can one use Earth's magnetic axial dipole field intensity to predict reversals?