Special Note: Please note that this scenario is meant to be read as entertainment, not as an accurate prediction of the future. Also note that the viewpoints and opinions that may come across in this scenario are not necessarily the viewpoints and opinions of the author.
Cities tend to be darker and hotter than the surrounding countryside due to the buildings blocking the sunlight. The real reason behind global warming is that our world is becoming more urbanized; thus making more places darker and hotter (even if everyone was forced to use mass transit in every city and every town on Earth). We could make the cities (and the earth) cooler by re-wilding (transforming abandoned buildings into forests).
Re-wilding efforts must also take future population growth into mind in addition to long-term regional economic growth patterns.
The trees would block the carbon caused by the tall buildings and the cars; making our cities cooler again like the surrounding countryside. The same can be done for the huge cattle farms in the rural areas once in vitro meat and vertical farming have been proven to be better for the environment than conventional farming and ultimately replace traditional farming.
Churches and other religious buildings that are too badly maintain to be converted into housing and businesses may also be converted back to forest land depending on air and water purity. Oversight from the government and the private sector will determine the suitability of the conversion of land usage. There are plenty of brownfield manufacturing plants that can be reconfigured into condominiums in a slumping real estate market. Re-wilding will ensure that the real estate market will never be overstimulated as to avoid inflating the local currency literally to death. Too much forests will block future housing projects while not enough forests will aggravate global warming.
By turning urban wastes and abandoned farms back into wilderness (Like most "Run-Down" sections of "Rust-Belt" Cities in the Northern US and Southern Canada), we could mitigate the effects of global warming. If television becomes illegal, it is likely people will have more time to explore these new wilderness areas, burn calories (in conjunction with a vegan diet), and finally end the obesity epidemic once and for all. The success behind the virtually unmanned nanofactories will also contribute to need to re-wild areas occupied with abandoned industrial buildings from the other centuries of human occupation with forests that can provide oxygen for us all. If we don't need the buildings and they don't need meet current standards, why not demolish them and plant a forest in their place?
It would provide a much nicer local aura, higher property values, and lower crime rates if we took those abandoned factories in Toronto, Detroit, Baltimore, St. Louis and Miami and finally got around to bulldozing them; planting forests where they once existed. Getting rid of buildings that nobody plans to use and restore them to their pristine wooded conditions are essential in boosting the morale of both residents and tourists alike; even given the recent economic circumstances that force people to search far and wide for decent-paying jobs.
However, this would destroy many people's livelihoods as people are forced to move away from places people have lived in for generations. This might either create a inner-city dominated by Mega Skyscrapers; home to thousands of poor residents or create large new low-Income suburbs dominated by househusbands and female service workers. And disrupt the general look of older cities with wild land that covers the space between the inner city and the suburbs.
Many major North American cities were not built in forests (Los Angeles was once very dry brushland, Washington, D.C. was considered to be swamp land prior to 1800). Rewilding may create large sections of desert or swamp in a major city; reintroducing "rural" dangers to an urban environment