They are invisible by definition, but a new camera can see them, and it's showing a radically different world billowing all around us.
Humanity's heat-trapping greenhouse gases, the main cause of global warming , are being made visible by the "gas finder" cameras developed by FLIR Systems.
They show massive dark plumes rising from some tailpipes and exhaust vents.
Working with FLIR scientists and engineers, ABC's graphics artists added effects to video of roadways and planes so that they show how the world might look if we could actually see greenhouse emissions .
The effect is startling - far more pollution rising into the air than we ever actually see from vehicle tailpipes and factory smokestacks.
"Not seeing it means you don't have a real appreciation of the problem," FLIR vice president Tom Scanlon told ABC News on a tour of the FLIR plant on the edge of Boston.
Greenhouse gases , which include carbon dioxide, methane and other gases, cannot be seen because their molecules are shaped so as to allow the hot light from the sun to pass through - like the clear glass of a greenhouse, while trapping the heat.
And when that sunlight warms the ground, its energy converts to heat that radiates back toward space also in the form of light, but in a different wavelength called infrared.
But because of the particular shape of greenhouse gas molecules, the heat from the space-bound infrared light remains trapped inside the earth's atmosphere.
That's global warming.
TV News reports about global warming are often slightly misleading when they show smokestacks emitting white steam and grey smoke. These are visible droplets or particles being carried by invisible gases.
Called "aerosols," these droplets and particles actually help cool the earth by reflecting the visible sunlight right back into space.
But once the particles fall from the air, or the steam condenses as precipitation, the invisible gases carrying them - often largely CO2 - are left to trap more heat radiating from the earth.
Most CO2 stays in the atmosphere for centuries, piling up, unlike particles and steam which usually fall out or condense in a matter of days or weeks.
It's probably no coincidence that the many of the harmful fossil fuel emissions we can see - including lung-clogging sooty black emissions from tailpipes and smokestacks - were already regulated some years ago in the U.S. and other developed nations.
The psychological impact would likely be great if we could actually see all the excess CO2 and other greenhouse gases rising all around us.
FLIR cameras are now being used by companies that want to find expensive or dangerous leaks of other greenhouse gases - such as sulfur hexafluoride (which has 23,900 times the greenhouse effect of CO2 and is found in power line transformers,) and methane which can cause explosions. But none are being used so far to detect C02.
Scanlon and scientist-engineer Bob Benson showed ABC News some video images of large dark puffs of gas escaping from a pipe sticking from a storage tank.
"This is gas escaping from a vent pipe in a tank" explained Scanlon, "and completely invisible to anybody that happens to be walking around this plant."
They also showed video of invisible CO2 - normal breath - coming out of a man's mouth as he breathed. It looked like the condensed vapor in your breath on a very cold day.