[en] Model calculations of the climatic impact of the increasing atmospheric carbon dioxide (CO₂) concentration consistently suggest that a doubling of the CO₂ concentration would lead to a warming of global average surface air temperatures by as much as several degrees Celsius. In this appendix, this controversy about the effect of CO₂ on climate is reviewed. Because the surface energy balance approach to estimating climate sensitivity has been the source of much of the controversy, a review of this approach is presented. It is shown that prior applications of this approach violate the law of conservation of energy (the first law of thermodynamics); therefore, these results are incorrect. Empirical data indicating the relationship between atmospheric emittance and surface vapor pressure and surface air temperature are shown to be consistent with climate model calculations. Consequently, it is not the experimental data that are the basis of the controversy, but rather the analysis and interpretation of these data