Some climate activists are cooling on a carbon tax A carbon tax is popular among economists, but it is increasingly out of favor among left-wing climate activists, who are pushing for a Green New Deal—100 percent of energy in the United States produced by clean, renewable, and zero-emission sources. Draw a graph of the U.S. market for energy to compare the effects of a carbon tax and a Green New Deal if the marginal cost of energy from renewables is less that the marginal social cost of energy from carbon sources.