In Climate Casino, Nordhaus discusses the difference between carbon taxes and cap-and-trade programs in Ch. 20. He says a major difference is that "The price of carbon would fluctuate under a cap-and-trade regime while the quantity of CO2 emitted would remain constant. Under a carbon tax, the quantity emitted would fluctuate while the price would be stable." Shifts in supply or demand in the electricity market could generate such fluctuations.