Using the mathematical formalism of the Brazilian Proposal to the IPCC, we analyse eight power technologies with regard to their past and potential future contributions to global warming. Taking into account detailed bottom-up technology characteristics we define the mitigation potential of each technology in terms of avoided temperature increase by comparing a coal-only reference scenario and an alternative low-carbon scenario. Historically (1900-2006), hydro, nuclear, and gas-fired power have achieved the largest mitigation. This ranking is partly due to the magnitudes at which these technologies are deployed, but in part also due to their deployment histories. Similarly, potential future (2009-2100) contributions are influenced by the magnitude of future capacity as well as temporal deployment profiles. A general conclusion is that early technology deployment matters. We conclusively show that avoided temperature increase is a better proxy for comparing technologies with regard to their impact on climate change, and that comparisons based on annual or even cumulative emissions may be misleading. Therefore, not only comparisons between countries, but also comparisons between technologies should be undertaken on the basis of avoided temperature increase rather than on the basis of annual emissions as is practice today.
