Solar absorption spectra in the infrared spectral region require line-by-line codes to retrieve the concentrations of molecules in the atmosphere from measured spectra. Since millions of spectral lines are observed we developed our own line-by-line code to find automatically the best suitable lines for the analysis. This code has been further developed to calculate the upwelling and downwelling radiation in the atmosphere. The code has been applied to study the Antarctic atmosphere, where a negative greenhouse effect is observed, which means the radiation to space is larger then the upwelling radiation from the surface. The reason for the negative greenhouse effect will be discussed in detail. Furthermore, the radiation budget for increasing greenhouse gases will be discussed for Antarctica and compared to the Arctic. The longwave upwelling and downwelling radiation throughout the whole atmosphere will be studied, a comparison to satellite data and models will be presented. The code has now been further developed to calculate the warming/cooling of the atmosphere. First results will be presented.