Taxing and nudging to reduce carbon emissions: Results from an online shopping experiment

What can be done to reduce the carbon footprint of consumption? To answer this, we conducted an online shopping experiment that tested the effects of two policy tools: a carbon tax (at two levels) and a behavioral nudge in the form of a traffic light-style label indicating a product's carbon footprint (green for low, orange for medium, and red for high). To disentangle the tax's substitution effect from its income effect, we held consumers' purchasing power constant. We find that the tax alone significantly reduces the carbon footprint per euro spent but not per basket purchased, implying that the reduction is driven purely by the income effect. The label alone makes consumers buy fewer red products and more green products, although without reducing significantly their carbon footprint. We do find some substitution effect and a significant reduction of the carbon footprint per basket only when the tax is high enough and combined with the label. Next, we perform a welfare analysis grounded on a theoretical framework that accommodates for several assumptions about consumer's preferences and motivations. We estimate the loss of consumer's surplus from nudging consumers with the label. We also estimate the consumers' valuation of a ton of CO2 avoided when they care about their climate impact.