When I bought  a bag of chips in England it had some bad news printed on the back. First, the chips had 14 grams of fat. Bad enough. Worse, they had caused 75 grams of carbon to be released.

That bag called my attention to my carbon footprint: those 75 grams added to the 2.3 million from the plane I took there and back, plus the total of all the carbon impacts of everything else I do and buy. Call it carbon guilt, but just thinking about it gets me depressed.

Enter the good news: handprints, the sum total of all the positive changes we make that lower our footprint. That’s something we can feel good about.

To know precisely how big our carbon prints are we need to do the math on what we buy and do. The metrics for this come from life cycle assessment, or LCA, which was used to calculate the carbon released over the entire life history of those chips, from the planting of the potatoes to tossing the empty bag in the trash.

Handprints are the brain child of Gregory Norris, who teaches LCA at the Harvard School of Public Health. He has set up a website [RUTH: url TK] that let’s us calculate our handprint and pledge or confirm ways we intend to enlarge it – with a Facebook status update about the action.

One neat feature: if your friends do the same because they learned from you (like boosting fuel efficiency by inflating their tires to the correct pressure), your handprint increases, too. The more people we recruit, the bigger our handprint (picture a girl scout troop going door to door with tire gauges and pumps). Now there’s a feature just waiting for a gaming app – one way more beneficial than becoming “mayor” of the water cooler.

This could grow into a market force for a cooler planet. The more we all pursue our handprints, the greater the financial incentives for eco-friendly innovations like the new carbon-negative cement (5% of the human carbon footprint is from cement) that stores carbon instead of releasing it.

Elke Weber, a cognitive scientist at Columbia University’s Earth Institute, says the handprint might remedy a major reason so few people go from awareness of global warming to ongoing action. When folks harp on the harm we do to the planet we feel bad and want to do something to feel better – and then we tune out. But if we have a positive goal in mind that we can take small, manageable steps toward, we feel good — and so are more likely to keep going.

Any group has a handprint, the sum total of its activities. Norris envisions a day when individuals and families, schools and clubs, companies and cities – maybe even nations – would compete on the size of their handprints.

Now that’s a game where we’d all be winners.

A slightly different version of this article ran recently in Time.