In This Issue
Summer Issue of The Bridge on Energy, the Environment, and Climate Change
July 3, 2015 Volume 45 Issue 2

Guest Editor's Note

Friday, July 3, 2015

Author: Robert C. Armstrong

The Challenges of Meeting Energy Demands in Environmentally Responsible Ways

Growing global energy demand, driven by population growth and rising standards of living in developing countries, suggests a global appetite for energy in 2050 roughly double that of today. At the same time, the IPCC Fifth Assessment (IPCC 2013) points out the urgency to reduce the carbon footprint of the global energy system. The dual challenge is thus to both double global energy supply by midcentury and simultaneously reduce carbon emissions.

Although climate change is the major environmental impact of the current energy system, attention is increasingly focused on the system’s water and land impacts. There are complex interactions between energy and land, air, and water. For example, water is needed for many forms of energy production, (e.g., for fracking in shale gas production and for cooling in thermal power plants) and conversely energy is important in producing clean water (e.g., for desalination operations and for pumping to places where water is needed).

Articles in this issue of the Bridge look at some of the key coupled energy-environment challenges, examining impacts of energy processes on climate change, water use, and land use, as well as technologies that are likely to be critical in efforts to meet growing energy demands in a carbon-constrained world. Of particular interest are biofuels, especially for transportation, and solar and nuclear energy for electricity production.

The issues of interlocking energy, economic, and environmental systems are framed in the first paper, by John Reilly. He shows model predictions of projected energy demand growth and impacts on global and regional temperature increases, land use, and water stress if current trends continue. New science, technology, and policies are needed to transform today’s energy system to meet human economic needs as well as to protect the environment. As he points out, energy demand growth will be greatest outside of the developed world.

Robert Jackson, Pierre Friedlingstein, Josep Canadell, and Robbie Andrew take a more detailed look at impacts of greenhouse gas (GHG) emissions on rising global mean temperature, assessing what it would take to limit that rise to 2–3°C. Looking at overall CO2 (and equivalents) in the atmosphere, they examine different scenarios of CO2 emissions reduction—a switch to renewables, carbon capture and storage (CCS)—to estimate when the CO2 emissions budget for the 2°C and 3°C targets will be reached. Their article certainly underscores the urgency of action.

Adam Brandt and Gabrielle Pétron survey natural gas opportunities and issues. Natural gas is recognized as a national and global resource that can play a special role in a transition to a low-carbon future (MIT 2011): it offers the triple opportunity to lower carbon emissions (particularly in the electricity sector), enhance energy security, and stimulate economic growth. But there are also concerns about potential negative impacts of its production and distribution, particularly methane leakage and risks to water supplies. This article focuses on the first of these two concerns, with a careful review and analysis of fugitive emissions and air quality impacts. Solutions to minimize such emissions are necessary to enable the full benefits of natural gas resources.

Transportation accounted for about 27 percent of total energy use in the United States in 2013 (EIA 2015, p. E-2), dominated by liquid fuels, primarily petroleum products. The two leading options for fuel replacement in this sector appear to be renewable liquid fuels, such as those derived from biomass, or electrification of the transportation system, complementing ongoing energy efficiency improvements in the vehicle fleet. Chris Somerville and Stephen Long discuss opportunities for biofuels in the energy mix, with a focus on liquid transportation fuels, where such alternatives offer considerable convenience and familiarity for consumers. The authors describe the major sources of liquid biofuels and technologies for conversion, and then discuss their climate (net GHG emissions), land, and food impacts. A particularly intriguing option is advanced biofuels with CCS, which might be carbon negative.

Solar energy is the zero-carbon technology that has the largest upside in scale and thus is likely to play a key role in 2050 and beyond in the presence of carbon constraints. Much progress has been made in recent decades in reducing costs of solar electricity, but it is still more expensive than fossil-generated electricity in the absence of a carbon price. Nathan Lewis and Daniel Nocera (NAS) review the state of solar energy technologies such as photovoltaics, concentrated solar thermal power, and solar-to-fuel technologies. As they show, all of the technologies have made impressive progress, but interesting research and development challenges remain.1 A very important area addressed in their article is the use of solar energy to produce fuels, which could provide the very long term, large-scale storage that a solar-dominated energy system would likely require. Finally, they discuss the ability to make transportation fuels with reduced carbon dioxide, an approach that offers the intriguing possibility of “renewable gasoline” down the road.

Another way to firm the electricity system in a world dominated by intermittent renewables is nuclear power. An important aspect of this source of zero-carbon electricity is global experience with nuclear energy at scale. Brittany Guyer and Michael Golay examine the economic and regulatory conditions needed to foster renewed growth of nuclear power in the United States. Together with cost, safety, and waste disposal considerations, they make the case for federal support as key to the expanded use of nuclear power.

The articles in this issue clearly just scratch the surface of important energy-environment interactions as we work to meet the ever increasing needs of humanity for energy, food, and water; but I believe they capture the nature of the problems that must be addressed to be successful in reducing carbon emissions while ensuring adequate energy around the world.


EIA [US Energy Information Administration]. 2015. Annual Energy Outlook 2015 with Projections to 2040. Washington. Available at

IPCC [Intergovernmental Panel on Climate Change]. 2000. Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories. Section 2.7: Fugitive emissions from oil and gas operations. Geneva.

MIT [Massachusetts Institute of Technology]. 2011. The Future of Natural Gas: An Interdisciplinary MIT Study. Cambridge, MA. Available at

MIT. 2015. The Future of Solar Energy: An Interdisciplinary MIT Study. Cambridge, MA. Available at Future of Solar Energy Study_compressed.pdf.


 1 More information on solar-to-electricity technologies, costs, system integration issues, and needed research and development is in the recently released Future of Solar Energy study (MIT 2015)

About the Author:Robert C. Armstrong (NAE) is director of the Energy Initiative and Chevron Professor of Chemical Engineering at the Massachusetts Institute of Technology.