The synergy of submillimetre and infrared spectroscopy in predicting global warming effects of CFC replacement molecules

The evaluation of the global warming effects of the CFC replacement gases is of very considerable interest following the Kyoto summit, since the main replacements, the HFCs are predicted to have both high global warming potential and atmospheric lifetimes of hundreds of years. In order to assess global warming potential it is essential to have available accurate temperature dependent absorption cross sections of the CFC replacement gases, particularly the HFCs. This requires not only the development of accurate and reproducible ways of experimental measurement of absorption cross sections, but also better methods of modelling their temperature dependence. Much of this has been developed by the authors as part of the SWAGG consortium. The CFC replacement gases, the HFCs, CF/sub 3/H, CH/sub 2/F/sub 2/, C/sub 2/F/sub 6/ and CF/sub 3/CH/sub 3/ are used as examples of the measurement and interpretation of cross sections, of the evaluation of the effects of the low frequency torsional modes whose spectra occur in the submillimetre region, and of the temperature dependence of the absorption cross sections. This encompasses techniques for freezing out torsional hot bands, strategies for line by line calculations of the spectra of heavy molecules of this type, and the input of the resulting cross section information into radiation transport codes in K. Shine's group in the Department of Meteorology at Reading University. The spectra were recorded using two Fourier transform spectrometers.