Sustainable Energy - Without the Hot Air
by David J.C. MacKay
Also available for free
If you want to know the scale of the sustainable energy/climate change problems we face, and what scale the possible solutions need to be, get this book.
Small Is Beautiful: A Study of Economics as if People Mattered
by E F Schumacher
Schumacher argues that the modern economy is unsustainable. Natural resources (like fossil fuels), are treated as expendable income, when in fact they should be treated as capital, since they are not renewable, and thus subject to eventual depletion. The revolutionary ideas are as pertinent, inspirational and thought-provoking today as when they were first published in 1973.