A co-benefit is an additional, positive consequence of a policy or project, beyond its primary goal.
There are often substantial and multiple co-benefits resulting from policies or projects aimed at protecting or restoring the natural environment. Particularly common among them are improvements in public health.
For example, improving walkability in urban areas in order to reduce automobile usage — and thus reduce greenhouse gas emissions — can result in people getting more exercise and thereby lower the incidence of metabolic diseases such as obesity, diabetes and heart disease. It can also provide additional co-benefits, including reduced traffic noise and fewer disabilities and deaths from traffic accidents.
Likewise, protecting sensitive habitats from sprawl in order to save endangered species can help support local economies by increasing recreation opportunities, promoting job creation, increasing revenue for local businesses, and raising property values. In some cases, the economic co-benefits can be truly substantial.
Passive use value is also a major co-benefit of many environmental protection projects. Passive use value is the value that people place on the existence of a species or habitat independent of their direct use of it, including the value of knowing that future generations will benefit from its preservation.
Co-benefits are similar to positive externalities in that both refer to positive outcomes beyond the primary effects, and the difference is largely one of emphasis or context. In general, co-benefits refer to intentional, additional benefits alongside the primary goals and are often used in policy and political considerations, whereas positive externalities are unintended, uncompensated benefits to third parties.
Negative co-benefits are secondary, negative effects of a policy or project. An example would be soil erosion, water contamination and air pollution from the mining and refining of rare earth metals for use in electric automobiles, which are being promoted as a means of reducing greenhouse gas emissions and air pollution.