It is much more likely that we are presently in a Geomagnetic excursion than in a full geomagnetic Reversal

If you study the history of these things there are many more geomagnetic excursions than full geomagnetic reversals. Also, I'm not sure if these events have anything at all to do with ice ages as they come either because there is likely a 50% chance we are presently headed sooner or later to an ice age in the next 1000 to 10,000 years.

So, I'm not sure how global warming events that often bring ice ages are what we are dealing with right now but I'm actually more sure we are in a geomagnetic excursion or reversal. However, even a geomagnetic excursion takes at least 1000 years and a geomagnetic reversal takes around 10,000 years or more to complete. But, the same effect to some degree is that there are major genetic changes to everything living above 10 feet underground or 50 feet from the surface in oceans or lakes around the world too.

So, as people learn more about this they might spend more time underground to protect themselves more from extreme genetic changes over time. Because of ever increasing winds in the form of hurricanes and tornadoes and other wind events worldwide living underground might be more efficient to in dealing with the ever increasing winds from Global Warming. (as long as you aren't living in a flood plain). If you lived in a flood plain you might need something like a submarine to keep you dry some times of the year if you were underground. But then how would you keep it from rusting from the elements underground over time?

Living underground likely is more efficient for heating and cooling the environment in a living space because temperatures stay more stable underground and don't change much in any 24 hour period worldwide. Also, they are impervious to winds on the surface and cannot be blown away like wooden houses can and are often around the world from hurricanes and tornadoes and other weather events.