One of the most poetic, intuitive but still urban-scale data displays around is "Nuage Vert" ("Green Cloud"), a low-wattage laser light illuminating the cloud that emanates from a coal burning power, in order to depict the energy-saving behavior of city inhabitants.
But it can get even better than that. Big Vortex [realities-united.de] is a winning architectural competition entry for a waste-to-energy plant for Copenhagen that stands out for its 2 unique features: its roof functions as a public ski slope for Copenhagen's citizens, and its smoke visualizes the side-effect of the waste-to-energy conversion in terms of tons of CO2 emission. Berlin-based artists realities:united modified the traditional smokestack so that gas clouds will take the shape of smoke rings (i.e. toroidal vortex shape), which become visible due to the condensation of water in the flue gases as they slowly rise and cool, before slowly resolving into the air.
The smoke rings will act as as gentle reminder of the residues of waste burning. In fact, each smoke ring, approximately 30 meters in diameter and 3 meter in height, constitutes exactly 1 ton of fossil carbon dioxide. This way the rather abstract pollution aspect, becomes somewhat more graspable and understandable. Depending on environmental conditions, the stability and visibility of these rings will vary, but an average each ring should be visible for about 45 seconds. At night, heat tracking lights will be used to position lasers onto the smoke rings turning them into glowing, communicative artworks.
Oh, and a pie chart might be projected onto the smoke, where the actual quota of fossil CO2 can be read. Really.