Can an impending reversal or excursion be detected from today's field?
In plain words
The main part of the field has weakened over the last two centuries and a weak patch over the South Atlantic is growing. It is unknown whether such signs announce a coming flip.
Precise statement
Using satellite-era, historical and archeomagnetic field models (axial dipole decline since about 1840, growth of the South Atlantic Anomaly), determine whether any observable statistic of the core-surface field forecasts a reversal or excursion within 1e3 to 1e4 yr with skill above chance. An answer is a forecasting statistic validated retrospectively on paleomagnetic records and on long dynamo simulations, or a demonstration, on long reversing dynamo simulations, that no core-surface statistic has skill above chance at these lead times.
What would settle it
Retrospective forecast tests on long reversing dynamo simulations and on high-resolution sediment records of past reversals and excursions.