David MacKay’s book (described here) makes an excellent point about the asymmetry between energy supply and demand, in terms of the difficulty or ease of increasing either:
It’s so simple for me to consume an extra 30 [kilowatt-hours] (kWh) per day. But squeezing an extra 30 kWh per day per person from renewables requires an industrialization of the environment so large it is hard to imagine.
For instance, buying a car and traveling 50 km per day in it means adding 40 kilowatt-hours per day (kWh/d) to your energy consumption. By contrast, surrounding all of the United Kingdom with wind turbines – with 15 per km of coastline, extending 4 km out to sea – would produce 16 kWh/d for every UK resident, if the wind was blowing all the time, and probably about 1/3 of that in actuality.
Statistics like that deepen my suspicion that a world without fossil fuel consumption will be one where there is much less energy consumption going on, overall. While increased efficiency can offset part of that, it also seems extremely likely that some very energy intensive activities will need to cease.