My take on greenhouse gas emissions
I think that we are probably very close to the peak oil peak or have already passed it. By that I mean that oil will only become more expensive over time. As it becomes more expensive a variety of methods will arrive to make living with expensive oil possible:
What probably won't work (in my opinion):
- Greater use of plug-in hybrid electric vehicles, some of these cars can go up to a 100 MPG (0.43 l/100 km) because most nights you'll plug it in and be able to drive around just on the amount you charged at night. You'll still have a motor and gas tank for those longer trips. Still, the biggest expense and weight are the batteries, however.
- Smaller and closer electric power plants. Some energy is lost because transmission through wires, this is reduced if the plant is closer. Smaller electrical plants are more likely to use newer and more innovative technologies.
- Increased use of wind power. People claim that there could never be enough wind (or solar) power to offset our addition to coal and oil. This is not true, more than twice the current electric energy generated in the US today could be generated by wind power alone (source). Right now wind power is growing rapidly.
- Increased use of solar panels. This can be used for heating water and seems (to me) ideal for air conditioning.
- Lighter cars. As more and more people look at the MPG rating of cars we'll start seeing more cars built with lighter, stronger materials.
- More efficient light bulbs. Compact fluorescent bulbs are already common, soon we may seen cheaper ultra-efficient LED bulbs.
- More public transportation. As gas prices go up, so should public transportation. The more people use public transportation the more convenient it becomes (because the transport authority provides more buses and routes).
- More nuclear power. There are two big complaints about nuclear: a) danger b) waste. The danger is a nuclear meltdown or a terrorist strike. The problem with waste is that there's no place to put it. It turns out that a terrorist strike is unlikely do anything and there are ways to make nuclear plants that are inherently safe. With regards to waste, there are ways of recycling the fuel. Currently we mine Uranium, use it once and dispose of 99% of the energy. If we recycled the "spent" Uranium we could use 99% of the energy and dispose of only 1% - and that 1% is have much lower half-life as well. Currently, it's cheaper to dig the Uranium from the ground, but if storage costs become way too high it would be far cheaper to reprocess the fuel. Reprocessing plants and reactors can be constructed so that they could never make weapons grade plutonium.
- Increased use of ethanol. Almost all cars sold here (Brazil) can use either ethanol or gasoline (or a mix) - a lot of cars also use propane. Most of our ethanol comes from sugar cane, using corn is not encouraged (switchgrass is pretty good however). Burning ethanol releases carbon dioxide, but is taken up again by the plants so it's really CO2 neutral.
- Less business traveling. As every computer begins to have pretty good teleconferencing and as air travel goes up in price we'll see more and more companies choosing not to send their people on business trips. Most people don't like traveling anyway, so it's not that hard a sell.
- Migration to the big cities. Living in the city is better for the environment than living in the suburbs (link). I hope to see a trend of more people choosing the city life.
- Smarter and more energy efficient homes. It's slowly becoming cheaper to have a smart home that turns on and off lights for you and uses fans and automatic blinds to keep the house warm or cool.
- CO2 economy. There's a chance that the CO2 market will grow to be important and should help to reduce CO2 emissions greatly.
What probably won't work (in my opinion):
- The hydrogen economy. Maybe eventually, but not anytime soon. There's a chance with fuel cells but it's a long shot.
- CO2 sequestering. The big problemI see are that it may bubble up out of the ground and kill people. I'm sure there will be some CO2 sequestering (especially if there's a CO2 market), but I wouldn't count on it being that important.
- Fusion energy. It's another possibility, but still a long shot as I see it.
You should add wind power to the list of things that don't work. Thousands of wind mills, all producing variable amounts of power, cause a grid management problem that is impossible to solve. A few nuclear reactors make all this mess unnecesary. Nuclear is so simple.
I've never heard the argument that cities cause low birth rates (there's stronger link to education of women and birth rate). I'm also not sure what you mean by 'sustainable' in this case. We want the world to be sustainable not the cities.