Although taxing carbon is an idea that enjoys significant support among policymakers and business leaders, new research indicates that carbon taxation can actually cause energy investments to gravitate away from the cleanest energy technologies. This counterintuitive finding reflects two key characteristics of energy markets: the worldwide increase in renewable energy sources whose output is intermittent and variable; and greater market liberalization, which has made the spot driving of electricity more volatile. The intermittency of renewable energy sources requires backup generation, typically from generators using fossil fuels. The dynamics of market liberalization amplify this negative effect of intermittency. Policymakers need to take steps to reduce intermittency by supporting storage technologies or setting monetary incentives to increase renewable generation capacity investment.