  Using kappa Ceti as a proxy for the young Sun we show that not only was the
young Sun much more effective in protecting the Earth environment from galactic
cosmic rays than the present day Sun; it also had flare and corona mass
ejection rates up to three orders of magnitude larger than the present day Sun.
The reduction in the galactic cosmic ray influx caused by the young Sun's
enhanced shielding capability has been suggested as a solution to what is known
as the faint young Sun paradox, i.e. the fact that the luminosity of the young
Sun was only around 75% of its present value when life started to evolve on our
planet around four billion years ago. This suggestion relies on the hypothesis
that the changing solar activity results in a changing influx of galactic
cosmic rays to the Earth, which results in a changing low-altitude cloud
coverage and thus a changing climate. Here we show how the larger corona mass
ejection rates of the young Sun would have had an effect on the climate with a
magnitude similar to the enhanced shielding capability of the young Sun.
