IPCC report
According to economic theory, if SCC estimates were complete and markets perfect, a carbon tax should be set equal to the SCC. Emission permits would also have a value equal to the SCC. In reality, however, markets are not perfect, SCC estimates are not complete, and externalities in the market are difficult to calculate accurately, resulting in an inaccurate carbon tax (Yohe "et al."., 2007:823). The 2018 IPCC report suggested that a tax of hundreds or even thousands of dollars per ton would be needed to drive carbon emissions to zero.