Etymology and definition

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In this review geoengineering is defined as intentional large-scale manipulation of the environment. Scale and intent play central roles in the definition. For an action to be geoengineering, the environmental change must be the primary goal rather than a side effect, and the intent and effect of the manipulation must be large in scale; e.g., continental to global. Two examples serve to demonstrate the roles of scale and intent. First, intent without scale. Ornamental gardening is the intentional manipulation of the environment to suit human desires, yet it is not geoengineering because neither the intended nor realized effect is large-scale. Second, scale without intent. The modification of global climate due to increasing atmospheric CO2 has global effect, yet it is not geo-engineering because it is a side effect resulting from combustion of fossil fuels with the aim of providing energy services.

Manipulations need not be aimed at changing the environment, but rather may aim to maintain a desired environmental state against perturbations -either natural or anthropogenic. Indeed, the term geoengineering has usually been applied to proposals to manipulate the environment with the goal of reducing undesired climate change caused by human influences. The focus of this review is likewise on climatic geoengineering, primarily - but not exclu sively - to counter CO2-induced climate change. In this usage geoengineering implies a countervailing measure or a "technical fix". As we will see, the definition of geoengineering is ambiguous, and the distinction between geoen-gineering and other responses to climate change is of degree, not of kind. Three core attributes will serve as markers of geoengineering: scale and intent, plus the degree to which the action is a countervailing measure.

The first use of geoengineering in approximately the sense defined above was by Marchetti in the early 1970s to describe the mitigation of the climatic impact of fossil fuel combustion by the injection of CO2 into the deep ocean (Marchetti, 1977). The term entered the mainstream of debate about climate change during the last decade, particularly with publication of the 1992 NAS assessment (see Table 10.1).

Geoengineering is not found in standard dictionaries. In technical usage it has at least one other not wholly unrelated meaning, as a contraction of geo-technical engineering: the "science that deals with the application of geology to engineering". If the definition above is accepted, a fitting etymology is readily constructed: geoengineering as geo- from the Greek root ge meaning earth and engineering meaning "the application of science to the optimum conversion of the resources of nature to the uses of humankind".

10.2.2 Geoengineering and carbon management

The long-term use of fossil energy without emissions of CO2 is an energy path that may substantially lower the economic cost of mitigating anthropogenic climate change. I call the required technologies Industrial Carbon Management (ICM), defined as the linked processes of capturing the carbon content of fossil fuels while generating carbon-free energy products such as electricity and hydrogen and sequestering the resulting CO2.

The distinction between ICM and geoengineering is both imprecise and interesting. In drawing the distinction we may first consider climatic geoengi-neering as a category of response to the CO2-climate problem. Figure 10.1 shows a simple schematic of the climate problem for which the response strategies are mitigation, geoengineering, or adaptation. In this scheme geoengin-eering is any manipulation of the climate system that alters its response to anthropogenic forcing; and the status of ICM is unclear because it resembles both conventional mitigation and geoengineering.

The definition adopted here emerges from an elaboration of the three-part schematic. It permits a clear distinction between mitigation of fossil fuel consumption and mitigation of CO2 emissions, and it draws the line between ICM and geoengineering at emission of CO2 to the active biosphere. Figure 10.2

Figure 10.1 Three-part schema of the climate problem. The black arrows in the top row show the causal chain in this version of the anthropogenic climate problem. The gray arrows and the second row define the modes of intervention.

Figure 10.2 Four-part schema of the climate problem. The interpretation follows that of Figure 10.1. Note the distinction between mitigation of fossil energy use, carbon management and geoengineering that illustrated the definition described in Section

Figure 10.2 Four-part schema of the climate problem. The interpretation follows that of Figure 10.1. Note the distinction between mitigation of fossil energy use, carbon management and geoengineering that illustrated the definition described in Section

shows a four-part schematic that illustrates the definition. It focuses on CO2, ignoring other anthropogenic climate forcings, and distinguishes between control of CO2 emissions to the active biosphere (ICM) and control of atmospheric CO2 post-emission (geoengineering). The implications of this distinction are discussed in the concluding section of the review.

10.3 History

10.3.1 Introduction

While the term geoengineering is an invention of the last few decades, explicit consideration of intentional large-scale manipulation of the environment has a history measured in centuries. This review focuses on the post-World War II history of weather and climate modification as a direct precursor to current thinking about geoengineering. Modern understanding of the CO2-climate problem emerged at a time when climate and weather modification was an important focus of science policy. Our aim is to explore the implications of this background for the treatment of proposals to employ countervailing measures in response to the CO2-climate problem.

While the focus here is post-World War II, the link between scientific understanding of the CO2-climate connection and proposals for its manipulation extends to the beginning of the twentieth century. Writing around 1905, Arrhenius speculated about a virtuous circle in which CO2 emissions from a growing fossil-fueled civilization would warm the climate, pushing back the northern limits of agriculture and so enhancing agricultural productivity as required to sustain the growth in population (Arrhenius, 1908). Similarly, Eckholm discussed the beneficial effects of elevated CO2, including effects on both climate and on plant growth, and speculated about the possibility of climate modification via engineered enhancements of CO2 emission (Ekholm,

The historical sketch presented here is necessarily incomplete, and its weaknesses highlight the absence of a thorough historical treatment of deliberate climate modification. While there are modern intellectual histories of climate change (Feming, 1998), and treatments of climate and weather modification that date from the 1970s (Taubenfeld, 1970; Green, 1977), there is little modern analysis that explores the links between weather and climate modification and current concerns about climate change.

As we will see, "weather and climate modification" or "weather control" was a centerpiece of research in the atmospheric sciences during the 1950s and 60s, and was viewed as a priority by the governments of the United States and the USSR. In that context what are now called climate impacts was then called inadvertent climate modification; and, what is now called geoengineering bears a strong similarity to what was then called weather and climate modification.

We may ask, what degree of continuity exists between the older concerns about deliberate and inadvertent climate modification and current concerns about climate impacts and geoengineering? With respect to inadvertent climate modification the case for continuity is strong. Consider, for example, the NAS66 report titled Weather and Climate Modification (see Table 10.1 for definition of the NASxx style mnemonics). The report contains an excellent summary of the CO2-climate problem in a chapter titled "Inadvertent Modification of Atmospheric Processes". This is the first extensive treatment of the climate problem in an NAS document, and it shares language and authorship with Restoring the Quality of our Environment (PSAC65), an early and influential assessment of the CO2-climate problem.

The correspondence between the 1960s concern with weather and climate modification and current discussion of geoengineering is less precise in that the aim of weather and climate modification was "improvement" of the natural state or mitigation of natural hazards, whereas the aim of recent geoengineer-ing proposals is the mitigation of anthropogenic hazards. Weather and climate modification therefore had two of the three defining attributes (Section 10.2.1) of geoengineering - scale and intent - but not the third, as it was not a countervailing measure. The case for continuity rests on the similarity of proposed technical methods, the continuity of citations to earlier work, a similarity of debate about legal and political problems, and finally, the strong resemblance of climate and weather modification to geoengineering as defined here.

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