In the beginning of October 2008, we saw a Blackberry app (Carbon Diem) that tracks your carbon footprint based on GPS data. Today, Clear Standards’ just released their version for the iPhone, the Carbon Tracker app. Without looking too deeply into the technical parameters I’m assuming it, too, deduces carbon output based on your traveling speed and location.
Update: Looks like you just punch in distance and mode of transport and it determines your footprint. Not nearly as cool as I initially thought.
The Carbon Tracker app is available here for free.