Sustainability and Energy Conversions
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stainability and Energy Conversions
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Sally M. Benson (Stanford University, USA) Franklin M. Orr, Jr. (Stanford University, USA)
CO2 Sequestration
Abstract A sustainable global energy system requires a transition away from energy sources with high greenhouse emissions. Vast energy resources are available to meet our needs, and technology pathways for making this transition exist. Lowering the cost and increasing the reliability and quality of energy from sustainable energy sources will facilitate this transition. Changing the world’s energy systems is a huge challenge, but it is one that can be undertaken now with improvements in energy efficiency and with continuing deployment of a variety of technologies. Numerous opportunities exist for research in material sciences to contribute to this global-scale challenge.
Introduction
More than six billion people occupy our planet at present, and in this century, several billion more will join us. Feeding, clothing, and housing all of us will be a significant challenge, as will supplying the fresh water, heat, lights, and transportation that we will need to live comfortable and productive lives, while also maintaining and preserving habitats for the species with whom we share the planet. It is also clear that we humans are interacting at local, regional, and global scales with the natural systems that we count on to provide us with many services. Local air and water quality depend strongly on the way we transport ourselves, manufacture all manner of products, grow food, and handle the wastes we generate. Humans now use a significant fraction of the fresh water available on Earth, and we recognize that air pollution emitted in one location can affect air quality over large distances. A decades-long effort in developed economies to reduce impacts on local and regional air and water quality has been very successful (although challenges remain); efforts to address global-scale environmental impacts are just beginning. Energy use, along with agriculture, which makes heavy use of energy for fertilizers, cultivation, and transportation of products, is a prime component of the interaction of human activities with global-scale natural systems through the emissions of greenhouse gases. As an example of the global impact of our energy systems, Figure 1 shows concentrations of important greenhouse gases over the past 20,000 years.1 Significant increases in atmospheric concentrations of the key greenhouse gases carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have been observed over the 250 years since the beginning of the industrial revolution. Increasing greenhouse gas concentrations cause capture of additional energy in the atmosphere over pre-industrial levels, with climate change as one result. In addition, the pH of the upper ocean has declined as the additional CO2 in the atmosphere slowly equilibrates with seawater.2 Lowering pH (i.e., increasing acidity) affects the concentrations of key ions, carbonate and bicarbonate, which, in turn, affect th
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