How much did your last trip to a grocery store cost you? How long did it take? Those are two questions that you probably feel confident about answering (though your perception of cost is likely lower than reality if you went by car), but what about the amount of greenhouse gases produced?

If you travelled by non-motorised modes you can be fairly sure that it cost you next to nothing and produced negligible greenhouse gases such as carbon dioxide (CO₂).  But what about if you took a bus, a tram, or a car? Do you think it was about 100g? 500g? 1kg? A tonne? If you're like most people you probably aren't really sure and if you think you know, just how sustainable is that value?

For money, we have a budget. There's a certain amount coming in and we can make judgements about what expenditures are appropriate with respect to that amount. For time, there's a budget as well and we have a general sense of what is too long and how long we're willing to spend to get somewhere.

Until recently, however most people didn't consider CO₂ and related information wasn't really available. In countries like the United Kingdom (UK), the amount of CO₂ produced per kilometre (km) corresponds to a tax band, so it affects the total price of purchasing a new vehicle. But do we really understand the mass of CO₂ produced per km? Can we contextualise it? E.g, do we know if that's a "sustainable" amount? Of course, "sustainable" will depend on a number of aspects of your life, not just transport.

Information about the CO₂ we produce in our daily lives can be found through programs like carbon calculator websites (e.g. Act On CO₂).  However, the results are often given as a weight (e.g. 6. 8 tonnes) or it might say how many trees are required to sequester the carbon, or maybe it says how many Earths would be required if everyone produced  the same as you.

So which increases understanding? Understanding is key to increasing awareness, which according to the theory of planned behaviour impacts the motivation to change. Without much background knowledge it's hard to contextualise the weight information. The equivalent amount of trees gives us a concrete representation of the gas, and we're all familiar with trees. But, do we know what's sustainable? The Earth format does give a sense of the limits within which we're working - our budget if you will. But it's still pretty abstract, isn't it? Other than the astronauts among us, we probably haven't seen the earth.

Preliminary results from research carried out by researchers at the University of the West of England suggest that out of those three, the equivalent amount in trees resulted in fewer people answering "I don?t know" and more answers that were close to the objective level of sustainability. The earth format was second, but many people found it either too small when dealing with highly sustainable transport like riding a full bus or unbelievable when considering high energy users like a 4x4 truck.

But understanding doesn't mean motivation to change. If weight was understood, perhaps it could motivate change. What about trees or earths? Is there an emotional reaction? If you saw that your transport choice alone required an entire earth to support (if everyone else behaved the same), would that inspire you to change more than images of 15 trees? When those formats were used in a question related to changing driving behaviour, the tree format was associated with greater motivation to change.

The ability of information to create real behaviour change is limited and this is only one aspect of the whole project. Future articles will discuss motivations other than environmental ones and practitioner needs with respect to implementing sustainable transport projects.

This is one example of research carried out for the CATCH project that will not only contribute to the project itself, but will hopefully lead to improved design of websites that seek to increase awareness about personal CO₂ production.