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Prolegomenon: A Geoengineering Primer

Martin Beech

Department of Physics, Campion College at the University of Regina, Regina, Saskatchewan, Canada

Abstract

Geoengineering encompasses many potential actions that set out to deliberately lower the aggregate temperature of the Earth's atmosphere. Such actions typically look to enhance the Earth's albedo, thereby causing a greater fraction of sunlight, over and above that at the present time, to be reflected back into space. Other actions seek to limit solar insolation by directly blocking sunlight, or by increasing cloud cover. This introduction seeks to examine not only how but why geoengineering might be deployed, but seeks to position it as a necessary part of future efforts directed towards combating global warming. A review is made of the various methodologies and protocols necessary for the future development and deployment of geoengineering actions.

Keywords: Global warming, geoengineering, tipping points, solar radiation management

1.1 Introduction

Geoengineering [1.1] [1.2] [1.3] is a big, bold and brash idea, possibly now coming of age. It is a human-directed process, taking-on many potential forms, all of which act upon the environment with the specific aim of changing the environment. The primary reason for and goal of geoengineering1 is to attempt the re-establishment of a common good-that is, to bring about a cooler Earth. Furthermore, geoengineering sits amongst the suite of actions that seek to address the principle causes of global warming [1.4]. This being said, geoengineering is often considered a controversial action, in part, because of the fact that it seeks to enhance human engagement with the environment, rather than reduce it. Importantly, however, while geoengineering seeks to cool the Earth's atmosphere, it does not address the root cause issues that are driving the global warming problem. While geoengineering is a strategic ameliorating action, it is limited in scope.

That a decision concerning the deployment of geoengineering must to be made, and made very soon, reflects a remarkable, and inherently unsatisfactory state of affairs-a state of affairs that has grown out of past and present-day inaction. This stubborn inaction is related to the prolonged political and societal failure in addressing the underlying causes of global warming-especially in the form of greenhouse gas emissions derived from the burning of fossil fuels. It is now established beyond any reasonable doubt that the Earth's average temperature is increasing, and compared to past millennia, it is increasing very rapidly. In the past one-hundred years alone, the global average temperature has increased by about 1.1 °C [1.1] [1.2] [1.3]. Global warming, in spite of tergiversate counter arguments, is indisputably happening, and it will be with us for many centuries to come. Indeed, even if all anthropogenic derived greenhouse gas emissions stopped this very instant, the present levels of atmospheric CO2 will continue to drive a significant increase in the Earth's temperature. The question is not whether global warming will continue to occur, but rather, what can be done now, and over the next several decades, to offset the worst of the changes that are latent within Earth's climate system [1.4] [1.5].

1.2 The Paris Agreement

While the reasonability of using the Earth's average temperature as the only measure of climate change is questionable [1.6], this quantity has, none the less, become the de facto measure of change. In this manner global warming is measured relative to the average temperature derived over the time interval from 1850 to 1900 (see Figure 1.1). This parameterization builds upon the notion that human actions (beginning with the onset of the modern industrial era) are at the core of the global warming phenomenon, and it further sets the goal of limiting future increases in temperature (above pre-industrial levels) to be as small as possible. Article 2(a) of the Paris Agreement contains the key motivation with respect to international efforts to curb global warming [1.7] [1.8], specifically, the aim being to:

[Hold] the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.

As with most political agreements, and especially international ones, the language promotes the positive, and downplays the devil in the details. The devil, in this case, is how to achieve the success of Article 2(a). The problem is not so much how to achieve this-of course, the solution is in fact quite clear-rather, the problem is how to overcome the political inertia (even outright hostility from some quarters) to enact and abide by policies that will dramatically reduce the emission of greenhouse gases due to anthropogenic actions. The Paris Agreement may well indicate a landmark moment in political diplomacy, but the proof by which it will be judged in the future will depend entirely upon the meaningful and timely actions taken by individual governments over the next several decades. Indeed, it is highly likely that the goals of Article 2(a) will not be achieved [1.9], with the global average temperature most likely exceeding 1.5 °C above pre-industrial levels by the mid-point of this century, if not sooner (Figure 1.1).

Geoengineering is motivated according to the dramatic increase in the Earth's average temperature during the last century (as per Figure 1.1)-the desire being to reduce its continued increase prior to the implementation of direct actions to limit and sequester greenhouse gas emissions. While the average global temperature provides a measure of how much the Earth is warming, detailed computer modeling and ground-based observations indicate that the warming is not uniform across the globe. Indeed, warming is most pronounced in northern latitudes and especially so over land masses. Figure 1.2 shows the results from a series of detailed model calculations, performed under the guise of the Coupled Model Intercomparison Project Phase 6 (GMIP6). At a 1.5 °C temperature increase over the (1850-1900) average-similar to the Earth's present status-it is seen that the northern boreal and Arctic regions are seeing the greatest temperature increases, with the equatorial and southern hemisphere temperatures seeing smaller temperature changes. At 4 °C average temperature change, the northern latitudes are still most dramatically affected, but now all landmasses and the Antarctic regions begin to see significant temperature increases. In general, at a given latitude, the landmass temperature increase is about twice that found over the ocean. This is partly a result of the oceans having a larger thermal inertia, and partly due to mixing with deeper, colder water layers that have not been exposed to surface warming. Changes in the Arctic are larger than those at mid-latitudes in part due to a strong temperature/albedo positive-feedback mechanism that operates there. The regional effects of temperature change are complex and difficult to model in detail, but are generally discussed in terms of tipping points.

Figure 1.1 Change in global average temperature during the past 2000 years, inferred (blue line) from proxy tree-ring, coral growth, and ice-core data [1.10], and measured (red line) since 1880.

(Image adapted from https://commons.wikimedia.org/wiki/File:Common_Era_Temperature.svg)

Figure 1.2 Projected changes in regional temperature (relative to 1850-1900) for global average warming amounting to 1.5 °C (top) and 4.0 °C (bottom).

(Diagram based on Coupled Model Intercomparison Project Phase 6 (CMIP6) calculations)

1.3 Tipping Points - Where Are We?

Current projections by the Intergovernmental Panel on Climate Change (IPCC) indicate that the Earth is likely to warm by at least 2 to 3 °C by the end of this century, and this increase will risk, if not fully guarantee, the triggering of multiple highly consequential tipping points. Indeed, tipping points delineate and underscore the risks associated with global warming. They highlight those moments and conditions under which an abrupt and rapid change, from one system state to another, takes place in an irreversible manner [1.11]. Tipping points are a characteristic phenomenon of nonlinear systems, and once breached they cannot be reset by simply reversing the driving parameters that caused the change in the first place. In the passing of a tipping point, what were previously system-stabilizing, negative feedback, mechanisms become overpowered by system-destabilizing, positive feedback mechanisms, with the system experiencing continuous change until a new equilibrium state is found. Problematically, the Earth's climate-determining system is composed of numerous nonlinear, subtly interacting subsystems, each operating on different size and time scales, and, as such, it is an extremely complicated system to model. A recent study by McKay et al., however, has identified 16 tipping point thresholds that may be breached by 2100 [1.12]. These include the collapse of polar ice sheets, large-scale permafrost...