The intensity of earth's magnetic field has been weakening in the last couple of hundred years, leading some scientists to think that its polarity might be about to flip. But the field's intensity may simply be coming down from an abnormal high rather than approaching a reversal, scientists write in a new paper in the Proceedings of the National Academy of Sciences. Humans have lived through dips in the field's intensity before, and there are debates about whether reversals in the more distant past had any connection to species extinctions. Today, we have something else today that would be affected by weakening of the magnetic field alone: technology. The magnetic field deflects the solar wind and cosmic rays. When the field is weaker, more radiation gets through, which can disrupt power grids and satellite communications.

"The field may be decreasing rapidly, but we're not yet down to the long-term average. In 100 years, the field may even go back the other direction [in intensity]," said Dennis Kent, an expert in paleomagnetism at Columbia University's Lamont-Doherty Earth Observatory and co-author of the study with his former student, Huapel Wang, now a post-doctoral research associate at MIT, and Pierre Rochette of Aix-Marseille Université.

The scientists used a new technique to measure changes in the magnetic field's strength in the past and found that its long-term average intensity over the past five million years was much weaker than the global database of paleointensity suggests - only about 60 percent of the field's strength today. The findings raise questions both about claims that the magnetic field may be nearing a reversal and about the database itself.

The study's results fit expectations that the magnetic field's intensity at the poles should be twice its intensity at the equator. In contrast, the time-averaged intensity calculated from the PINT paleointensity database doesn't meet the two-to-one, poles-to-equator dipole hypothesis, and the database calculation suggests that the long-term average intensity over the past 5 million years is similar to the field's intensity today.