What is the cost of 1 ton of a greenhouse gas? When a climate-warming gas such as carbon dioxide or methane is emitted into the atmosphere, its impacts may be felt years and even decades into the future—in the form of rising sea levels, changes in agricultural productivity, or more extreme weather events, such as droughts, floods, and heat waves. Those impacts are quantified in a metric called the "social cost of carbon," considered a vital tool for making sound and efficient climate policies.