  Magnetic monopoles have a long history of theoretical predictions and
experimental searches, carrying direct implications for fundamental concepts
such as electric charge quantization. We analyze in detail for the first time
magnetic monopole production from collisions of cosmic rays bombarding the
atmosphere. This source of monopoles is independent of cosmology, has been
active throughout Earth's history, and supplies an irreducible monopole flux
for all terrestrial experiments. Using results for robust atmospheric fixed
target experiment flux of monopoles, we systematically establish direct
comparisons of previous ambient monopole searches with monopole searches at
particle colliders and set leading limits on magnetic monopole production in
the $\sim 5-100$ TeV mass-range.
