  Using a summary curve of two eigen vectors of solar magnetic field
oscillations derived with Principal Components Analysis (PCA) from synoptic
maps for solar cycles 21-24 as a proxy of solar activity, we extrapolate this
curve backwards three millennia revealing 9 grand cycles lasting 350-400 years
each. The summary curve shows a remarkable resemblance to the past sunspot and
terrestrial activity: grand minima - Maunder Minimum (1645-1715 AD), Wolf
minimum (1280-1350 AD), Oort minimum (1010-1050 AD) and Homer minimum (800-900
BC); grand maxima - modern warm period (1990-2015), medieval warm period
(900-1200 AD), Roman warm period (400-10 BC) and others. We verify the
extrapolated activity curve by the pre-telescope observations of large sunspots
with naked eye, by comparing the observed and simulated butterfly diagrams for
Maunder Minimum (MM), by a maximum of the terrestrial temperature and extremely
intense terrestrial auroras seen in the past grand cycle occurred in 14-16
centuries. We confirm the occurrence of upcoming Modern grand minimum in
2020-2053, which will have a shorter duration (3 cycles) and, thus, higher
solar activity compared to MM. We argue that Sporer minimum (1450-1550) derived
from the increased abundances of isotopes 14C and 10Be is likely produced by a
strong increase of the terrestrial background radiation caused by the galactic
cosmic rays of powerful supernovae.
