We update predictions for lepton fluxes from the hadroproduction of charm
quarks in the scattering of primary cosmic rays with the Earth's atmosphere.
The calculation of charm-pair hadroproduction applies the latest results from
perturbative QCD through next-to-next-to-leading order and modern parton
distributions, together with estimates on various sources of uncertainties. Our
predictions for the lepton fluxes turn out to be compatible, within the
uncertainty band, with recent results in the literature. However, by taking
into account contributions neglected in previous works, our total uncertainties
are much larger. The predictions are crucial for the interpretation of results
from neutrino experiments like IceCube, when disentangling signals of neutrinos
of astrophysical origin from the atmospheric background.Comment: 40 pages, 24 figure