Information provision is frequently used to motivate prosocial behavior, yet its impacts on welfare are rarely measured. I study these impacts by combining a signaling model with a series of randomized experiments on personal carbon emissions. The model generates predictions for how information provision can directly affect consumer welfare by altering the relationship between emissions and inferred altruistic type. I implement three interventions, two that provide participants with private information about their emissions and one that publicly reveals them, and measure their welfare effects with an incentive-compatible willingness to pay elicitation. The private information interventions are positive-sum in consumer welfare, whereas public recognition is negative-sum. Nevertheless, 16 to 25 percent of participants pay to avoid receiving private information. Under public recognition, relatively high emitters incur significant utility losses while relatively low emitters receive no gains. I use these estimates to compare the social efficiency of different forms of information provision on externalities.