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Summary
The history of past major energy transitions—from wood to coal, and from coal to oil and gas—suggests that it will be a long, tough road to scaling up alternatives to fossil fuels that don't stoke greenhouse warming. A big problem is that, for the first time, the world is moving to tap new energy sources that are, in many ways, less useful and convenient than the currently dominant sources: fossil fuels. Oil in particular is densely packed with energy, easily transported and stored, and efficient at releasing its energy in modern engines. Renewables are another matter. Fuel sources like corn kernels or wood chips tend to be bulky, and their energy content is diffuse. Planting energy crops and building solar or wind farms is a land-hungry process, and the energy they deliver is often intermittent and hard to store.
