Ben (S0) often talks about the implications of a 'solar magnetic shutdown,' or Sunspot Grand Minima, as it harbours the potential for the next mini-ice age. A central theme is that low/weak solar activity brings about a drop in heliospheric strength, pressure thereby making the entire Solar System more susceptible to the effects of Galactic Cosmic Rays (GCRs). Cosmic Rays are currently being researched as inducers of lightning, cloud formation, ozone depletion and global cooling.
The effects of low solar activity, high cosmic ray activity are not just significant factors for planetary climate, they can also play a leading role in changing a planet's biosphere as well.
This review covers several of the signatures of cosmic ray variability, with the authors Atri and Melott hoping that "These assumptions will improve with our understanding of the production mechanisms of high and ultra-high energy cosmic rays and properties of their sources. Terrestrial effects include damage from solar UVB through ozone depletion, secondary muons and lightning discharge. Radiation doses from various astrophysical sources can be calculated and their biological effects can be estimated."
Sounds good, Let's dig in…
The Sun is the primary source of radiation here on Earth, "The total solar irradiance (TSI) is eight orders of magnitude larger in energy flux than cosmic rays…However, in order to have an effect on the biosphere, the radiation should be capable of significantly altering the atmospheric chemistry and/or generating secondary particles so that the radiation dose on the ground is increased significantly" (Atri & Melott 2014).
We know that the geomagnetic field is a good shield against solar particles, and as a result solar particles do not have a significant effect on the biosphere at large (except for solar storms), "However, since the magnetic field lines guide the charged particles towards the magnetic poles, even low energy particles can impact life in polar regions" (Atri & Melott 2014).
We also know that 'The Force That Protects Our Planet' has weakened by 15% over the last 150 years. The magnetic deviation, the difference in location between magnetic north and true north, has a gap that's been growing at an increasing rate: before 1994 it was estimated that the magnetic north pole was moving about 10 km/year, however, since 2001 it has increased to about 65 km/year. So not only is the magnetosphere weaker, but the location of the magnetic north pole is shifting as well and we can't forget about how energetic particles love to spiral along those magnetic field 'lines.'
According to the European Space Agency: "the poles have reversed, on average, about once every 200,000-300,000 years. Reversals are a slow process and do not happen with regularity…the last time this happened was about 780,000 years ago."