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Another hypothetical use-your-imagination bit inspired from the news.
blaisepascal
I was listening to a report on NPR from the UAE a couple of days ago. One of the things they mentioned was that the UAE is planning to build a "carbon free city of the future."

What would be a "carbon free city"?


I'm not stupid... I'm not a total literalist. It's obvious that by "carbon free" they mean, most likely, neutral in production of organic "greenhouse gasses".

But it's fun to take things literally, sometimes. What would a "carbon free city" be like -- what would it take to make one? Since the inhabitants are human, and we are not carbon-free, and the food we eat can't be carbon-free, I'm willing to imagine a carbon-free city infrastructure would be sufficient. So buildings, utilities, facilities, etc, all carbon free. What would that mean?

Some things are easy to imagine: no wood, no plastics, electricity used would probably have to be either hydro-electric (not likely in the UAE) or nuclear, not oil, coal, or natural gas. Wind power might work, but I don't know how much steady wind there is in the UAE. Most likely nuclear (not that there's anything wrong with that).

No plastics leads to a tricky bit: modern insulation of electrical wiring is thermoplastic, usually PVC. To go carbon free, we'll have to find a replacement. At a guess, I think silicones are in city of the future.

Heating is simple with electric heat, but I'm not sure how much that is necessary in the UAE. Cooling is not as simple. Most, if not all, modern refrigerants are organic. The only one I can think of offhand that isn't is ammonia. So we have at least one (albeit inefficient) refrigerant that can be used.

But the trickiest part is building materials. We've already eliminated wood and likewise paper products, insulations like blown cellulose, expanded polyurethane, etc. We could insulate with loose fiberglass, but not fiberglass batts with paper backing. We'll have to be careful about construction adhesives. I live the the North East US and work for a company involved in energy efficient construction, so I tend to think in terms of stick construction with insulation, plastic vapor-barriers, sheathing, etc. That's what we use around here. I think the UAE probably is more likely to use concrete, brick, or similar bulk-material construction techniques.

The good news is that cement, used in making concrete, is carbon-free, consisting mainly of calcium silicates. The bad news is that it's made from limestone, which is calcium carbonate, and making cement drives off the carbon in the form of carbon dioxide. But in the finished product there's no carbon. So no cement factories in our city, but lots of cement.

Just not steel-reinforced concrete. Here's a more difficult challenge: steel, a ubiquitous building material, is an alloy of iron and carbon. There are iron alloys which don't use carbon, but they are not used for structural purposes so its hard to decide what would be good for a replacement for steel reinforcement. Aluminum is cheap, readily available, comes in many alloys, but is readily corroded in wet alkaline environments. Unfortunately, curing cement is a very alkaline wet environment. I don't know a good replacement off hand.

Anyone else want to play in this game? What else would go into a carbon-free city?

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I work in the carbon game, because I am analyst in the mass transit division, and naturally professional email lists are plentiful on 'carbon offsets'. There are many ways to create this.

The most common is to find a way to net reduce your own emissions. In other words, re-appopriating methane gas from landfills to power buildings. Placing specialty filters on mass transit vehicles to reduce emissions to near zero, and fueling them with ULSD-Electric Hybrids. (Ultra Low Sulfur Diesel) And yes, you mention several green construction options.

There is also carbon-trading or the offset market. Basically, this is where a city or company counts its output of carbon, and ten pays an emissions expert to equivalently start a program elsewhere to lower it. As you might suspect, I find the whole carbon-emissions-trading regime to be a bit shady. I much prefer the attempt to reduce one's own pollutants and be responsible, than to do the environmental equivalent of purchasing middle-ages era indulgences (via the Catholic Church - for all reading who are not familiar, you can wikipedia it).

For those interested: you can check out www.wiserearth.org or the Green Building Council's website. Now fair warning: don't take every idea you see there and assume it's really 'carbon neutral'. A number of ideas are just plain out there, so use some common sense. That said, there's a few ideas to consider for carbon-neutral cities.

Yes, I'm in a similar business. Taking them at what they meant I'm sure there are lots of ways they could do it. But taking them literally (a city built without carbon) is a different matter.

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