The Earth's magnetic polarity field might be reversing .

Relatively non-catastrophic, the planetary magnetic flip is an event that is normal but aperiodic. It leaves only minuscule geological evidence, but that evidence is legible in the magnetic orientation of iron particles within the lava that emanates from mid-oceanic rifts at a roughly-steady rate.

Humans don't know its effect upon organisms because the most-recent occurence of it was before we evolved.

While normal, the occurence is not regular. It has happened twice in as little as a few tens of thousands of years; and it's also not happened for as long as tens of millions. The term "non-catastrophic" is indeed relative. Magnetic navigating systems are going to fall into chaos during the millenia of alteration, and will require a recalibration after complete reversal.

Some species, presumably, won't adapt.

Also, there is going to be some effect upon the shielding by the magnetosphere against various outer-space radiation frequencies, mostly solar.

The most-recent polarity reversal was about 780,000 years ago.