Timescale for different cooling losses in years (synchrotron,inverse Compton, ionization and bremsstrahlung) as a function of magnetic field strength in μG at z = 0 for a cosmic ray energy of 1 GeV, an ISM density of 1 cm^-3 and a radiation field of 10^-12 erg cm^-3 as typical for the Milky Way. The timescales are evaluated at the frequency ν_c corresponding to the peak synchrotron emission. We find here that synchrotron losses dominate above magnetic field strengths of ∼10 μG.