This is an interesting question. Depends on what "global changes" you mean. Some weather disruption? Entirely possible, but to be honest, weather does not depend *directly* on the earth's magnetic field, but only indirectly, which complicates matters. Changes to the weather would be most likely to occur because, during the period of the actual pole switch, the earth's magnetic field is suppressed, which will allow more high-energy cosmic and solar radiation to hit the upper atmosphere, which _may_ have the effect of driving cloud formation in the upper atmosphere (the jury is still out on this one, but see http://www.env.leeds.ac.uk/research/ias/aerosols/cosmic.htm or http://www.eawag.ch/publications/eawagnews/www_en58/en58e_screen/en58e_beer_clouds_s.pdf for research that has been done in this area). More cloud in the upper atmosphere can have effects on how much of the sun's light and heat penetrate or are trapped inside the atmosphere, which in turn drives weather effects. The magnetic pole flipping will absolutely certainly have some global effects on a number of fish and migratory birds, since there is good evidence that many species use the lines of magnetic force around the earth to orient themselves. Given how many species have already had their population hugely reduced by human activities, we might see some migratory species go extinct entirely if they lose the ability to navigate to their usual feeding or breeding grounds. And, there is some evidence that during periods in the past where there has been a similar pole shift, the increased levels of cosmic radiation which find their way through the atmosphere have increased the background rate of mutation. Note that we are NOT talking about cancerous tumors erupting all over people standing in the street or generations of monsters being born -- we are talking about a somewhat elevated rate of skin and other cancers, and organisms carrying a few more mutations in every generation than they usually do (bear in mind that the vast majority of genetic mutations are "silent", that is, they have no effect on the organism whatsoever. Of the mutations which have any effect, most will be detrimental, but 10-25% of them can be beneficial). However, the overall effect is likely to be very small and subtle. Even when the earth's magnetic field is at its strongest, the field near the poles allows a lot of radiation through, and mutational rates in organisms near the poles is only a bit higher than anywhere else. The only thing which could exacerbate this effect is the fact that we have loaded the upper atmosphere with CFCs. The degradation of the ozone layer via CFCs currently only happens at the poles, because it is at the poles that the magnetic field is weakest and diverts the least UV radiation; and high-energy solar UV radiation is what reacts with CFCs to drive the chemical reactions. CFCs themselves are no more prevalent over the poles than in the upper atmosphere anywhere else on earth, though, and if the magnetic field weakens over the rest of the planet we would expect to see the area of ozone degradation spread. (Incidentally, please note -- just because you don't see the "ozone hole" in the news any more, does not mean that it does not exist or that it has gone away. See http://jwocky.gsfc.nasa.gov/multi/multi.html for NASA's media files of the ozone hole, or http://ozonewatch.gsfc.nasa.gov/ for NASA's "ozone hole watch" over the south pole.) And finally, the one thing in the human world which we know would be affected is radio, TV and satellite communication, since increased levels of radiation will interfere with all of these. This may have knock-on effects with things like GPS, if the GPS units can't speak to satellites well enough, or the satellites aren't functioning well enough, to position themselves. Overall the effect would resemble what we get during particularly bad sunspot periods. We will also get some really spectacular auroral lights, visible well toward the equator. See http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html or http://en.wikipedia.org/wiki/Magnetosphere for a diagram of how the earth's magnetic field affects the radiation which reaches us, and more on the magnetosphere. Glenn -- please note, the "ozone hole" is the popular designation of the thinning of the ozone layer, and as such is used even by NASA. Don't rate me down for reporting popular terminology, please. And do a little reading -- the earth's magnetic field protects the upper atmosphere from being blasted by solar radiation except at the poles, which is why ozone degradation happens there - as I report. Of COURSE UV gets through in other areas -- just not as much.