Reducing the risk of catastrophic climate change will require leveling off greenhouse gas emissions over the short term and reducing emissions by an estimated 60-80% over the long term. To achieve these reductions, we argue that policymakers and regulators should focus not only on factories and other industrial sources of emissions but also on individuals. We construct a model that demonstrates that individuals contribute roughly one-third of carbon dioxide emissions in the United States. This one-third share accounts for roughly 8% of the world's total, more than the total emissions of any other country except China, and more than several continents. We contend that it is desirable, if not imperative, that governments address emissions from individual behavior. This task will be difficult because individual behaviors, including idling cars and wasting electricity, are resistant to change, even when the change is rational. Mindful of the costs, we propose measures that have a high likelihood of success. We draw on norms theory and empirical studies to demonstrate how legal reforms can tie the widely held abstract norm of personal responsibility to the emerging concrete norm of carbon neutrality. We suggest that these legal reforms could push carbon neutrality past a tipping point, directly influencing many carbon-emitting individual behaviors and building the public support necessary for policymakers to address the remaining sources.