Comparative Impacts of Fossil Fuels and Alternative Energy Sources

KLAUS S. LACKNER

1 Introduction

Growing concerns over the consequences of climate change may severely limit future access to fossil fuels. A forced choice between energy and environment could precipitate a major economic crisis, an environmental crisis, or both. Averting such a crisis will be difficult, because fossil energy resources are an essential part of the world's energy supply and climate change is mainly driven by the build-up of carbon dioxide in the atmosphere. Carbon dioxide (CO2) is the unavoidable product of fossil fuel consumption. Therefore, the use of fossil fuels collides directly with global environmental concerns. Unfortunately, fossil fuels are difficult to replace, but stabilising the atmospheric concentration of carbon dioxide requires a nearly complete transition to a carbon-neutral economy. This implies either the abandonment of fossil fuels or the introduction of carbon capture and storage, whereby for every ton of carbon extracted from the ground another ton of carbon is put back.

This chapter discusses the scope of the required reduction in carbon dioxide emissions and the options available for achieving such reductions. It puts the continued use of fossil fuels, with carbon capture and storage, in context with other approaches toward achieving a carbon-neutral energy infrastructure or otherwise avoiding serious climate change impacts.

The vast scale of energy infrastructures emerges as the central theme. There are very few energy resources that are large enough to cope with modern global energy demand. Any technology that will be able to satisfy these demands will unavoidably interfere with natural dynamic systems. Just like some of the large natural cycles, human energy systems are operating on a global scale. It is the vast scale of human energy demand that shapes the available options.

2 Climate Change

The idea that greenhouse gases in the atmosphere control climate is not new. While travelling with Napoleon through Egypt, Fourier was the first to recognise that the composition of a planetary atmosphere regulates a planet's surface temperature. Some sixty years later, Tyndall measured the absorption spectrum of CO2 in the infrared region. His laboratory measurements showed that carbon dioxide is a powerful greenhouse gas, which is largely responsible for the habitable temperature range on Earth. In 1898, Arrhenius was the first to quantify the greenhouse effect and estimate the impact of anthropogenic emissions of CO2. While extensive research and numerical studies have added much detail to our understanding, his initial ideas remain unchanged. Computer models and observations corroborate the basic insights developed in the nineteenth century.

Fossil fuels provide 81% of the world's commercial energy supply. Consumption of fossil fuels produces nearly 30 Pg (petagram) of carbon dioxide annually. Until now, nearly all of this carbon dioxide has been released to the atmosphere. In the past, the atmospheric sink was considered large enough to accommodate any additional carbon dioxide, but the carbon dioxide content of the atmosphere has now risen by more than a third since the beginning of the industrial revolution, from 280 parts per million by volume (ppm) to 385 ppm today.

Fossil fuel combustion is the single most important contributor to this change. The total carbon dioxide produced in the combustion of fossil fuel since the beginning of the industrial revolution actually exceeds the observed increase in the atmosphere. At present, the carbon dioxide content of the atmosphere is rising by 2 ppm per year, suggesting that more than a third of the fossil carbon dioxide produced does not stay in the atmosphere.

The rapid increase in the atmospheric concentration of carbon dioxide has raised the spectre of severe climate change, and much effort has gone into understanding the likely scale and the implications of global warming. Today it is generally accepted that doubling of the carbon dioxide in the atmosphere would create serious harm and an often-cited goal for stabilising carbon dioxide in the atmosphere is 450 ppm, which at current rates of increase would be breached in about 30 years.

Carbon dioxide is an important greenhouse gas and the most obvious impact of CO2 release is global warming. However, CO2 is also physiologically active in plants and animals, it is of great importance to ecological systems and it is an acid that critically affects the chemistry of ocean water.

While the focus of the climate scientist is on the impact of CO2 on global warming, an important focus for the engineer developing a sustainable energy infrastructure is to eliminate the environmental impacts that arise from the release of carbon dioxide to the atmosphere. Even more broadly, the energy engineer has to consider the environmental consequences of generating power. In this context, it is the unintentional mobilisation of large quantities of carbon that needs to be eliminated. With a fossil energy infrastructure, the production of large quantities of oxidised carbon is unavoidable; their release into the atmosphere can and must be avoided.

The climate scientist will lump CO2 together with other greenhouse gases; the engineer of a sustainable energy infrastructure must find ways of stopping CO2 emissions. This will eliminate the climate change impact of carbon dioxide, as well as other impacts of excess carbon. The control or elimination of other greenhouse gases may also be necessary for stabilising climate. However, the control of these other greenhouse gases raises rather different issues and may occur outside of the energy sector. Thus, their management should be considered separately.

Unlike other emissions, carbon dioxide is not a problem at the point of emission. Carbon dioxide rarely reaches concentrations that constitute a local hazard. The ambient background level of CO2 is so high that mixing of CO2-rich plumes with the atmosphere reduces excess concentrations to a small fraction of the background already in the vicinity of the source. Carbon dioxide...