There are lessons from recent history of technology introductions which should not be forgotten when considering alternative energy technologies for carbon dioxide emission reductions.

The growth of the ecological footprint of a human population about to increase from 7B now to 9B in 2050 raises serious concerns about how to live both more efficiently and with less permanent impacts on the finite world. One present focus is the future of our climate, where the level of concern has prompted actions across the world in mitigation of the emissions of CO2. An examination of successful and failed introductions of technology over the last 200 years generates several lessons that should be kept in mind as we proceed to 80% decarbonize the world economy by 2050. I will argue that all the actions taken together until now to reduce our emissions of carbon dioxide will not achieve a serious reduction, and in some cases, they will actually make matters worse. In practice, the scale and the different specific engineering challenges of the decarbonization project are without precedent in human history. This means that any new technology introductions need to be able to meet the huge implied capabilities. An altogether more sophisticated public debate is urgently needed on appropriate actions that (i) considers the full range of threats to humanity, and (ii) weighs more carefully both the upsides and downsides of taking any action, and of not taking that action.