But at ground level, cosmic radiation accounts for apparently an average of around 11% of ionising radiation exposure and this is measurably affected by the interaction of the solar wind with the magnetosphere according to experiment, or at least according to the nice graph on this page - http://www.sievert-system.org/WebMasters/en/contenu_rayonnem...
[edit] I think I remember reading somewhere that a strong magnetosphere also reduces the erosion of the atmosphere, but I suspect that this would not be a particularly important effect over the timespan of a magnetic flip, otherwise we would not be here to worry about it.
[edit] Have just gone and had a good look at this and it would appear that while there is an increase in cosmic rays at the earth's surface when the magnetic field is reduced, this basically has negligible effect when compared to other sources of ionising radiation exposure - http://www-istp.gsfc.nasa.gov/Education/FAQs7.html#q104 - so I was talking monkey poo all along. Oh well. Quibble revoked.
[edit] I think I remember reading somewhere that a strong magnetosphere also reduces the erosion of the atmosphere, but I suspect that this would not be a particularly important effect over the timespan of a magnetic flip, otherwise we would not be here to worry about it.
[edit] Have just gone and had a good look at this and it would appear that while there is an increase in cosmic rays at the earth's surface when the magnetic field is reduced, this basically has negligible effect when compared to other sources of ionising radiation exposure - http://www-istp.gsfc.nasa.gov/Education/FAQs7.html#q104 - so I was talking monkey poo all along. Oh well. Quibble revoked.
However I did learn a little bit about oh-my-god particles while looking into this - http://www.fourmilab.ch/documents/OhMyGodParticle/ - which are really, really cool. :)