A world macroeconomic model E3MG is being developed to investigate policies for climate change and sustainable development, as a module of a new IAM structure. As climate change is a long term phenomenon, a model of long term economic changes is required. There is no suitable and generally accepted theory of long term technical change, but Freeman and Louca [1] have developed a good descriptive theory. This paper interprets this theory in quantitative terms, in the context of the macroeconomic analysis. It will outline a model of the changes in economic structure via Input-Output coefficients and the growth of new technology industries, incorporating endogenous technical change from R&D and investment, with learning-by-doing.