Policy Brief - Harvard Project on Climate Agreements, Belfer Center

The Optimal Energy Mix in Power Generation and the Contribution from Natural Gas in Reducing Carbon Emissions to 2030 and Beyond—Summary

  • Carlo Carraro
  • Massimo Tavoni
  • Thomas Longden
  • Giacomo Marangoni
| June 2015

The full discussion paper is available for download here: http://belfercenter.ksg.harvard.edu/publication/23833/


There is considerable tension between climate-policy goals and actual energy trends in the European Union (EU). On the one hand, the EU has pledged a 40% reduction in carbon dioxide emissions by 2030, relative to 1990, and its Emissions Trading System is the largest cap-and-trade program for carbon dioxide emissions in the world. On the other hand, EU energy consumption tilted toward more emissions-intensive sources from 2010 to 2012, not less: natural gas usage dropped 14% in that period, while coal usage rose 8%.

Given these trends, there is significant interest in a normative analysis of energy markets — that is, what energy mix is optimal for achieving a given environmental target. The authors conduct this type of analysis, focusing on EU power generation in the years 2010–2050. They begin by identifying a set of climate policy scenarios that vary along four primary dimensions: overall stringency of emissions-reduction targets; reliance on specific renewable energy requirements; the price of natural gas; and the scope of future energy efficiency regulation. Using an integrated model of global energy markets and economic outcomes, they then calculate the most cost-effective mix of coal, natural gas, nuclear, and renewable power generation that satisfies each policy scenario. Their findings highlight the importance of strong carbon pricing and a commitment to natural gas in the cost-effective attainment of climate goals.


The authors analyze four scenarios representing different levels of overarching policy stringency: A no-policy baseline; two EU-specific policy scenarios, with "moderate" and "stepped up" emissions reductions goals; and a global policy scenario, based on pledges made at the Durban Climate Change Conference of 2011, which aimed to restrict global temperature rise to 2° Celsius. Combining these policy goals with assumptions about technical and economic constraints on power systems, the authors compute optimal shares for each major power source over time, where "optimal" is defined as the least-cost energy mix that achieves the emissions target of each policy scenario. By varying three key model parameters — the presence of renewable energy requirements, the price of natural gas, and the scope of energy-efficiency improvements — the authors also examine the effects of plausible deviations from the four basic scenarios.

The analysis reveals a general trend of decreasing coal and nuclear use and increasing natural gas and renewables use in the optimal energy mix across all policy scenarios. However, this realignment of the energy market and climate objectives takes place only after 2020, when higher carbon prices (in $/ton of carbon dioxide (tCO2 )) are expected. Renewable requirements, gas prices, and energy efficiency improvements have a large effect on the precise price, quantity, and cost consequences of optimizing under each scenario. The 2020 targets for renewable energy, for instance, suppress the overall carbon price by an estimated 10 $/tCO2, which in turn slows the substitution of natural gas for coal and reduces revenues generated by auctioning off emissions allowances. Lower natural gas prices, on the other hand, have the effect of speeding up the penetration of natural gas into European power markets. Finally, the impact of energy efficiency improvements depends on the source of these improvements: efficiency gains due to reductions in emissions intensity (emissions per unit of power) produce cost savings relative to efficiency gains from reductions in overall energy demand (total power consumed).


  1. A strong, sustained carbon price is sufficient to realign market incentives with climate objectives. A price on carbon emissions incentivizes cleaner power generation regardless of fuel source. Furthermore, carbon pricing can generate revenues for financially stretched governments.
  2. Natural gas is very likely to be the key transitional fuel for reaching the optimal energy mix in a variety of policy scenarios. Even if renewable power targets restrict natural gas expansion in the near future, cost-effective achievement of all climate targets considered involves steep increases in gas consumption between 2020 and 2050.
  3. Subsidies for renewable power generation should be discontinued after 2020 if the carbon price is sufficiently high. Subsidies dampen carbon prices, increase policy costs, and reduce public revenues. Wind and solar power generation has the potential to rise over time even without subsidies, due to increasing cost-competitiveness and the incentives provided by a general carbon price.


The future of energy markets is highly uncertain, because it is inherently difficult to forecast energy demand growth, technological change, and the economic damages of climate change. Regardless of the EU's specific climate targets, however, this analysis suggests that a few conceptual guidelines can go a long way toward producing an energy mix that reduces emissions at minimum cost. Carbon pricing should be emphasized; subsidies for renewables or other specific fuel sources should be reduced over time; and energy efficiency policies should be designed to complement market based interventions.

For more information on this publication: Please contact Harvard Project on Climate Agreements
For Academic Citation: Carraro, Carlo, Massimo Tavoni, Thomas Longden, and Giacomo Marangoni. “The Optimal Energy Mix in Power Generation and the Contribution from Natural Gas in Reducing Carbon Emissions to 2030 and Beyond—Summary.” Policy Brief, Harvard Project on Climate Agreements, Belfer Center, June 2015.

The Authors