  We report in this letter for the first time the numerical simulations of muon
and neutron flux variations at the surface of the earth with varying air
densities in the troposphere and stratosphere. The simulated neutron and muon
flux variations are in very good agreement with the measured neutron flux
variation in Oulu and the muon flux variation in Atlanta. We conclude from this
study that the stratosphere air density variation dominates the effects on the
muon flux changes while the density variation in troposphere mainly influences
the neutron count variation. These results pave a new path for systematically
studying the global temperature evolution using worldwide cosmic ray data.
