Social cost in neoclassical economics is the sum of the private costs resulting from a transaction and the costs imposed on the consumers as a consequence of being exposed to the transaction for which they are not compensated or charged. In other words, it is the sum of private and external costs. This might be applied to any number of economic problems: for example, social cost of carbon has been explored to better understand the costs of carbon emissions for proposed economic solutions such as a carbon tax.

Carbon emission trading (also called carbon market, emission trading scheme (ETS) or cap and trade) is a type of emission trading scheme designed for carbon dioxide (CO2) and other greenhouse gases (GHG). It is a form of carbon pricing. Its purpose is to limit climate change by creating a market with limited allowances for emissions. This can reduce the competitiveness of fossil fuels, and instead accelerate investments into renewable energy, such as wind power and solar power. Fossil fuels are the main driver for climate change. They account for 89% of all CO2 emissions and 68% of all GHG emissions.