http://sciences.blogs.liberation.fr/home/files/Courtillot07EPSL.pdf [Broken] I have been looking into puzzling cyclic changes the geomagnetic field which appear to be solar driven as they match the solar magnetic cycle timing. The sun is moved by the large planets about its barycenter. The change in direction of the sun and its acceleration at the time of the change in its direction appear to interrupt the solar tachocline which is the interface between the solar radiative zone and convection zone. The tachocline is the region where sun spots are produced. When the tachocline is disturbed sunspots cannot long build in the tachocline. A sunspot requires a field strength of around 2000 gauss to avoid being torn to pieces as it moves from the bottom of the convection zone (tachocline) to the solar surface. The restart of the solar magnetic cycle appears to create massive coronal mass ejection CME which when they strike the earth's ionosphere create very large electrical discharges from the ionosphere to the planet's surface. The timing of perihelion and the earth's axis tilt at the time of the event controls which hemisphere the strike hits. I would assume the polarity of the strike remains the same. Depending on the polarity of the earth's magnetic field at the time of the event and the hemisphere the strike occurs in, determines whether the strike will reduce or increase the earth's magnetic field. This explains why the strike does not always have a strong cooling effect on the climate. Prior to the strike the solar magnetic cycle is in a deep minimum which cools the planet. The geomagnetic field resists changes so will initially weaken in the region of the strike before the effect is integrated into the total geomagnetic field constructively or de-constructively. The ice sheet insulate the planet and force the strike down to lower latitudes where it has less affect on creating the geomagnetic field. This explains why the geomagnetic field drops in intensity by 70% during the glacial phase of the glacial/interglacial cycle. It has been known for sometime that cosmogenic isotopes changes track the abrupt climate changes on the planet. Read this paper thinking about the above proposed mechanism.