It seems to me that someone could make a crescent-moon shaped artificial rift-like valley to catch a lot of sunlight in the colder months, with a transparent lid whose purpose was to keep in a much higher than natural concentration of carbon dioxide.
The purpose of the exercise to study the growth of plants in such a situation. It could likely pay for itself by growing superior quality produce.
There have been several such studies in greenhouses, at least one reported in Science magazine. Additional CO2 increases plant growth and reduces water consumption.