6. The energy challenge

Today, the world is faced with two constraints, and France with three:

1. The first concerns greenhouse gas emissions, and in particular CO ₂ from human activities. The time scale for responding to this problem is short.

2. The second constraint is that fossil fuels are in finite supply on earth and are gradually running out, even if we start to exploit unconventional resources such as shale oil and gas on a large scale. Within one or more centuries, oil will be scarce and expensive. We need to reduce our consumption of fossil fuels now, and replace them with other energy sources. Compared with the constraint of emitting less CO ₂ , the time scale for doing without fossil fuels is long.

3. The third...