New Scientist features a video from Carbon Visuals that shows carbon emissions in the form of 10 meter diameter spheres for every ton of carbon released into the air.
Each ball represents a ton of carbon dioxide: the volume of gas that would fill a sphere of that size. The video shows the mountain of balls that would build up after an hour, a day and a year, as well as visualising the emission rate of about two tons per second in real time, if it all emerged in one place.
The visualisation aims to give the general public a better understanding of greenhouse gas emissions by representing volume in a more intuitive way.
If you haven't signed up with 350.org yet, what are you waiting for?
Update: I'm seeing comments to the effect that New York City is doing a relatively good job on carbon emissions, thanks to mass transit, etc. True enough - but even so, that's still a pretty impressive mass of carbon. The idea of the visual is to show a city most people are familiar with, and what kind of carbon footprint it has. It's a way of showing just how big that impact is - and get people to wonder how big it is elsewhere. Because most carbon emissions are invisible to the unassisted eye, we don't really have an intuitive grasp of the magnitude of them. This is a tool to give us a starting point.
75% of that mass comes from buildings for example. Now imagine how that pile might change from more efficient energy/heating systems and insulation. Think how it would look if the amount from vehicles was coded a different color. What would it look like if we could see how much was being absorbed by coastal wetlands, trees, the ocean?
Humans aren't very good at thinking in numbers - but give us something to look at we can relate to the physical world and we can do a bit better. We already know we've got to start cutting back on the amount we're putting into the air. All the efficiency in the world on the part of New York City won't save it from rising sea levels if we don't cut back on the net amount going into the global atmosphere.