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1 Engineering the World’s Sunshine
- The MIT Press
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1 Engineering the World’s Sunshine [54.152.216.170] Project MUSE (2024-03-29 08:49 GMT) How might geoengineering work? Suppose the goal was to cut the rate of global warming in half starting in 2020 by putting sulfuric acid into the stratosphere. If combined with serious efforts to cut emissions, this is—in my opinion—a plausible scenario for managing the human and ecological risks of climate change in a world without politics. It is doable in the narrow technocratic sense that a wellmanaged program could likely be ready to start by 2020 if given a provisional go-ahead today and a total budget of roughly a billion dollars. This scenario is a tool with which we may explore the possible. It is not a prediction or plan.There are a handful of plausible geoengineering technologies and a case for climate engineering a host of ways they might be used including some that are immensely destructive. As a newly emerging and divisive idea, geoengineering will add to the confusion of climate politics. Though I hope to persuade you that it’s a good idea in the sense that it might be approved and swiftly implemented in some ideal global democracy, the chance of starting this scenario by 2020 seems slight. We lack the social tools to make sound collective decisions about planetary management . I will explore the politics that may shape realworld outcomes later in this book. To be effective, the sulfuric acid needs to be in tiny watery droplets—about a thousand times smaller than the width of a human hair—and it needs to be put into the stratosphere about 20 kilometers above the earth’s surface. Once there, the droplets will scatter sunlight back into space reducing the amount of sunlight reaching the ground. This slight shading effect tends to cool the planet, partially offsetting the warming effect of greenhouse gases such as carbon dioxide. Water droplets would do a fine job scattering david keith sunlight—any cloud does this—but they just don’t live long enough in the dry air of the stratosphere. The reason for using sulfuric acid is simply to keep the droplets from evaporating. Once formed the acid droplets remain in the stratosphere for about a year before falling into the lower atmosphere, so they must be continuously replenished. As carbon dioxide and other greenhouse gases accumulate in the atmosphere—and accumulate they will until humanity cut its emissions to nearly zero— the amount of sulfur needed to offset their warming grows year by year. After the first year of operation, the project would need to inject about 25 thousand tons per year of sulfur in order to offset half of that year’s growth in warming due to that years accumulation of greenhouse gases. The next year one would need to use 50 thousand tons to provide enough cooling to offset the half the warming from two years growth in the atmospheres stock of greenhouse gases. In 2030, after a decade of operation the injection rate would need to be 250 thousand tons per year.4 [54.152.216.170] Project MUSE (2024-03-29 08:49 GMT) a case for climate engineering It is not technically difficult to get sulfates into the stratosphere. The hardware to do this does not exist today, but it is nevertheless fair to say that the capability exists today in the sense that the required aircraft and dispersal technology could be engineered and built within a few years by many aerospace companies or governments.The technical challenge is not the sulfur dispersal hardware but rather the development of the science and observing tools to monitor the effectiveness and side-effects of a sulfate geoengineering program, but here too there are many tools that could be applied quickly. Injection of sulfates might be accomplished using Gulfstream business jets retrofitted with off-the-shelf low-bypass jet engines to allow them to fly at altitudes over sixty thousand feed along with the hardware required to generate and disperse the sulfuric acid. Only one or two aircraft would be needed to start the program , and after a decade it would take about ten aircraft to lift the required 250 thousand tons each year at an annual cost of about 700 million dollars. It would david keith then make sense to convert to purpose-built aircraft with longer wings better suited to high-altitude flight; this change would cut costs roughly in half and might allow...