Earth’s magnetic field is indeed weakening, and that could, over time, affect how well it protects us from the constant solar wind and more consequential solar storms, so good question. I didn’t go into it because the weakening is a very long-term phenomenon, and because it’d be yet another very complex thing to explain in this already lengthy story, and I tend to go off on lots of tangents that can make stories unwieldy. There’s a good piece on the weakening magnetic field on Space.com, and another one on Phys Org.

I also didn’t get into the potential effects of a bad solar storm on humans (in a really bad one, you probably don’t want to be flying over the Arctic, for example). EOS has a nifty, concise article about the latest study on risks in flight. Thanks for asking!