All kidding aside, this could have a significant effect on both weather and health. If weather patterns are related to magnetic field patterns, then the period of weakening and reversal would lead to weaker jet streams and more blocking, which might produce some disruptions to global agriculture. It would not be very predictable, more like an increased frequency of unusual events. The weaker magnetic field would also be less efficient at blocking ultra-violet and other radiation, increasing cancer rates.
It needs to be understood that this won’t just happen overnight. The magnetic field has been weakening steadily over the past century or more, and will continue to do so if we are in fact approaching a reversal. There would not be one year with the current polarity followed by a second year with the opposite polarity. There would be a period of hundreds and perhaps thousands of years of erratic polarity with weak secondary poles showing up and drifting around, some at rather low latitudes, in a transitional phase.
What remains to be seen is whether all of this would be a nuisance or a severe impact, and basically, we just don’t know. I don’t see much chance of it reaching those levels in this century, more like 2500-3000 AD for the reversal process to set in and possibly longer to complete.
According to current scientific understanding, governments can do nothing to prevent this, so the preparation would need to be in terms of potential responses. Even there, when only some of the impacts can even be guessed at, what response can there be? We are stuck with this happening in our future and will probably find that the impacts are so spread out over time that it will be a process of continual gradual adjustment (not all of it successful, possibly).
“The weaker magnetic field would also be less efficient at blocking ultra-violet and other radiation, increasing cancer rates.”
No. The magnetic field has nothing to do with blocking photons, like UV light. It steers particles (cosmic rays) away from most of the earth towards the poles, resulting in the auroras. A weakening magnetic field will affect health, since energetic cosmic rays can damage DNA. They also can damage electronics. This is why people are so interested in large coronal mass ejections (X flares) and the damage they might do to the electrical grid.