This paper tests the hypothesis that global warming would be detrimental to the global economy this century. It compares empirical data of energy expenditure and average temperatures of the US states and census divisions against projections using the FUND [1] energy impact functions holding time-dependent parameters, except temperature, constant at 2010 values. It finds that energy expenditure reduces as temperatures increase. This suggests that global warming, by itself, would reduce, not increase, US energy expenditure and so would have a positive, not a negative, impact on US economic growth. Next, these findings are compared against FUND energy expenditure projections for the world for the 21st century. The findings suggest that warming, by itself, would also reduce global energy expenditure. If these findings are correct, and if FUND projections of the non-energy impact sectors are valid, warming would benefit the global economy up to around 4˚ C increase in average global temperature from 1900. If this is true, the hypothesis is false. In this case, greenhouse gas mitigation policies are detrimental to the global economy. The analysis and conclusions warrant further investigation. We recommend the FUND energy impact functions be modified and recalibrated against empirical data.