I would propose the production of cities on slopes which produce electrical power food and water in excess of its occupants requirements.
In order for the solar powered cites proposed above to work the heat of the sun would be captured ( under a greenhouse ) and allowed to heat air and water. This warm air water vapor mixture being much lighter than ordinary air in the area will rush up slope and in doing so spin turbines. When the mixture gets to the top of the slope it would be chilled below the dew point, some water would be removed, and humid cool air possibly with water droplets in it would flow down the cold side.
People would live under the plastic greenhouse roof required to contain the air and grow crops where ever possible with different crops being located based on the crops requirements for heat and humidity.
On the cool side some of the incoming solar radiation will be captured in solar water heaters and that heat used to heat and provide humidity to the air going up the hot side. This will result in a partial shade which some plants grow very well in.
At night on the cool side the solar water heaters will radiate heat and so chill water which had already been cooled somewhat with evaporative coolers. This water would then be used in water sprays or panels to cool off the air going down the cool side of the city.
Most of the housing and other buildings needed for the people living and working there will be located under the sun lit surface which is in general used for food production. Light pipes or sky lights would be used to provide day light inside those buildings.
Water of any sort ( sea water would be fine) can be used to start the process and provide the system with extra water to carry away surplus heat. Note, this extra evaporation into a hot dry climate is almost certain to result in more clouds and rain somewhere which will make the earth somewhat cooler.
Almost all the usual waste materials of the people living in it would be recycled and over time the carbon contained in the plants and animals inside would increase. This will reduce the amount of carbon in the air generally.
Category of the action
Reducing emissions from electric power sector.
What actions do you propose?
As a start I propose construction of one such "Sloped Solar City" to test the power generation and other capacities so as to evaluate if many more should be constructed. The first such city should be a well funded international effort so that all the best technology and materials could be used to insure it is as good as it can be made. Additionally because it would be many different individuals contributing they could get similar efforts going in their own areas of the world. The universities of the world could also contribute by providing some course work at the cities for their students and perhaps a real world place to test technology developed by their faculty. As a way to make the power generation run twenty four hours a day, 365 days a year the cities would have thermal storage in them in the form of pure hot and cold water in large closed ponds so that even a few cloudy days or warm nights would not affect operations.
Who will take these actions?
The cities would be built where ever steep sun facing slopes are available especially in hot dry climates. Salt water can easily be piped to them provided such is available somewhere near by.
I expect that a country like Tunisia which is very hot and dry and has sites that are suitable would be able to provide land for such an initial city and then private investors could provide capital to get it built. In some cases I hope that for the initial "city" some suppliers could supply some materials which could be used as a way to get those materials or products tested in a real world laboratory type setting. Inaddition these cities should be a learning laboratory where students in all the disiplines of engineering could learn and work for a while. Since these cities would become home to a fairly large number of people eventually it would be important to have them made to be people friendly. To make that easier I would have them partitioned into villages of less than 200 people each but allow for easy travel from one to another.
Where will these actions be taken?
The first such city should be built in an area which is otherwise poorly suited for any productive use by humans because it is in a hot, dry area on a steeply sloping land surface that generally faces the sun. There are many such places in the United States and other countries. The best places to start may be in poor areas of the world where construction and land costs could be lower than in the developed world
How much will emissions be reduced or sequestered vs. business as usual levels?
The only emissions should be for actual construction and maintenance since once it is running only water vapor and salt should leave in excess of what is being taken in from make up air. It is possible this city could produce more food, water and electricity than it requires also further reducing the emissions somewhere else. This would mean nearly a 100% reduction in the normal emissions of a large city in addition to the reductions elsewhere if this city produces more electricity and or food and water than it requires internally.
What are other key benefits?
The key benefits are provison of a place for people to live and work while at the same time providing them with food, water, and electrical energy without a large carbon foot print. In additon these people might be able to provide food, pure water and electricity beyond what they themselves use to others in the area. Also if many such cities could be built they could be a safty measure to protect the survival of humanity in case we have a catistrophic event that distroys our traditional infrastructure since they would be so selfsufficient. Each citiy after completion should get a fairly good durable library of as much technical information as possible in case this benefit is truly called upon. Currently if we lost our major cities for what ever reason almost all of our advanced technology would also be lost.
What are the proposal’s costs?
Each such city would cost in the millions but no where near the cost of an ordinary down draft tower thousands of feet tall.
One such city , without all the underground buildings finished could be constructed in less than a year since it is a simple greenhouse built on a slope and uses ordinary technology which is currently available.