Amongst the plethora of packets and bottles, all presenting their data in different ways, it is nigh-on impossible to make an informed decision. But help may soon be at hand. A pilot study suggests that "augmented reality" smartphone apps could help people cut through the confusion and quickly compare the green credentials of different products. This could potentially be a powerful tool to reduce carbon footprints and could also improve public health.

At home, shopping is likely to be the biggest contributor to your carbon footprint no matter how much you turn your thermostat down. In the US indirect carbon dioxide emissions from consumer purchases are double the direct emissions from home energy use and personal travel, for example.

Douglas Arent from the US National Renewable Energy Laboratory and his colleagues envisage people using a smartphone to bring up pre-calculated information about individual products. That way consumers will clearly see the emissions embodied in a product, and be able to compare different brands directly.

In a pilot study, the team created an augmented reality app that enabled people to compare the embodied emissions in cereals and bottled water, when shopping at a major grocery store in Denver, Colorado. Beforehand Arent and his colleagues carried out detailed carbon footprint calculations for a wide range of brands of these two items. Once ready they recruited 126 people to use the app during two weeks in July 2015, and then fill out a short survey afterwards.

Consumers were asked to personalize the app by selecting the attributes that were important to them, such as whether they would prefer low-sugar options. Whilst shopping people could hover their phone at the cereal aisle, and see each box graded by a letter (A to F), providing a comparative "eco-rating". Zooming in on one particular box, shoppers could see the carbon ranking for that product, and any information pertinent to their previously selected attributes, such as the amount of sugar.

"Augmented reality gives additional information that shoppers can't necessarily find on the edge of a packet," said Arent.

The app helped consumers to reduce their carbon footprint by 23% when they were buying bottled water, the researchers found, but had a negligible effect on the carbon footprint of cereal purchases. The augmented reality app did appear to lead to people making healthier cereal purchases, with an average drop in 32% for sugar, 15% for fat and 9.8% for salt, plus a 47% increase in fibre content.

"Our consumer surveys afterwards indicated that people liked using the app and found it of value," said Arent, whose findings are published in Environmental Research Letters (ERL) .

In this case the personalized information, presented in real-time and an easy to understand way, helped people to make more informed decisions about their purchases. Ultimately Arent and his colleagues hope that the project can be rolled out on a much wider scale, potentially having a significant impact on carbon footprints and public health.

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