I have read in the last few days that during North hemisphere winter, the north pole sinks and the northern hemisphere shrinks, pulling the equator north a bit, so expanding the southern hemisphere. Total earth shape and size remain the same. This recent scientific discovery was reported in the lay press, but without mentioning the amount of movement.
1. How do they know - did GPS tell them?
2. Could GPS still give accurate positions when these movements are happening?
I suspect the answers to 1. and 2. are mutually exclusive.