Can you tell your readers that no "cosmic showers" whatsoever are expected? The shield will hold even if the geodynamo totally collapses, because solar wind induces a magnetic field on its own that is quite sufficient for shielding, see http://arxiv.org/abs/astro-ph/0404580. Furthermore, the magnetic field goes from dipolar to quadrupolar and only then reverses, and it is a very slow process:

...the average duration of a reversal is close to 7,000 years. The timescale of the transition differs at various latitudes. During the last polarity shift, approximately 790,000 years ago, sites close to the equator underwent the 180-degree change over the course of 2,000 years, but the process took closer to 10,000 years in midlatitude regions. Clement, BM Nature 428, 637−640(2004).
http://www.sciam.com/article.cfm?articleID=000ACB8C-81D1-1074-BCFA83414B7F0000

There was an excellent recent review on earth geodynamo in the April 2005 issue of scientific American that explains all of these points
http://www.sciam.com/article.cfm?articleID=000BDE84-BA70-1238-B9FA83414B7F00A7

In short, please, calm down. Life has been through uncounted such reversals and their effect is negligible. DO NOT PANIC! BTW, the next reversal is expected at 4000 AD.

Спасибо. Теперь я точно не буду паниковать и другим не посоветую. Всё движется очень постепенно и вполне безопасно.