David Keith
Patient Geoengineering
Practical geoengineering
“Temporary, moderate, and responsive” should be the guidelines of responsible geoengineering, in David Keith’s view. For slowing global warming, and giving humanity time to bring greenhouse gas emissions down to zero (and eventually past zero with carbon capture), he favors the form of “solar radiation management” that reflects sunlight the way volcanoes occasionally do—with sulfate particles in the stratosphere.
The common worry about geoengineering is that because it is so cheap ($1 billion a year) and easy, civilization would become “addicted“ and have to continue it forever, while giving up on the expensive and difficult process of reducing greenhouse gas emissions, thus making the long-term problem far worse. Keith’s solution is to design the geoengineering program as temporary from start to finish. “Temporary“ means shut it down by 2200. (Keith also likes the term “patient” for this approach.)
By “ moderate ” he means there is no attempt to completely offset the warming caused by us, but just cut the rate of climate change in half. That would give the highest benefit at lowest risk—minimal harmful effect on ozone and rainfall patterns, and the fewest unwelcome surprises, while providing enough time (and plenty of incentive) for societies to manage their carbon dioxide mitigation and orderly adaptation. Geoengineering’s leverage is very high—one gram of particles in the stratosphere prevents the warming caused by a ton of carbon dioxide.
“ Responsive ” means careful, gradual, and closely monitored, with the expectation there will be many adjustments along the way, along with the ability to back off entirely if needed. Though climate-change models keep improving, we still do not completely understand how climate works, and that raises the very good question: “How do you engineer a system whose behavior you don’t understand?” Keith’s answer is “feedback. We engineer and control many chaotic systems, such as high-performance aircraft, through precise feedback.” The same goes for governance of geoengineering. It is a complex system that will require sophisticated control by a global set of governing bodies, but we already do that for the far more complex system of global finance.
Keith’s specific program would begin with balloon tests in the lower stratosphere (8 miles up) releasing just 100 grams of sulfuric acid—about the amount of particles in a few minutes of normal jet contrail. “If those studies confirm safety and effectiveness,” Keith said, “then we could begin gradual deployment as early as 2020 with three business jets re-engineered for high altitude. By 2030 you could have about ten aircraft delivering a quarter million tons of sulfur per year at a cost of $700 million.“
The amount of sulfur being released might be up to a million tons by 2070, but that would still be only one-eighth of what went into the stratosphere from the Mt. Pinatubo volcanic eruption in 1991, and one-fiftieth of what enters the lower atmosphere from our current burning of fossil fuels. By then we may have developed more sophisticated particles than sulfate. It could be diamond dust, or alumina, or even something like a nanoscale “photophoretic” particle designed by Keith that would levitate itself above the stratosphere.
This is no quick fix. It is not quick, and it doesn’t try to be a complete fix. It has to be matched with total reduction of greenhouse gas emissions to zero and with effective capture of carbon, because the overload of carbon dioxide already in the atmosphere will stay there for a very long time unless removed. Keith asked, “Is it plausible that we will not figure out how to pull, say, five gigatons of carbon per year out of the air by 2075? I don’t buy it.“
Keith ended by proposing that goal should not be just 350 parts per million (ppm) of carbon dioxide in the atmosphere. (It’s rising past 400 ppm now.) We can shoot for the pre-industrial level of the 1770s. Take carbon dioxide down to 270 ppm.
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primer
In 01991, Mount Pinatubo – a largely forgotten and underestimated volcano in the Philippines – erupted in what would turn out to be one of the 20th century’s most significant geological events. It shot about 20 million tons of sulfur dioxide to the surface, much of which a coinciding typhoon then swept up into the air. This produced a cloud of sulfuric acid aerosols that quickly spread across the planet and managed to lower global temperatures by about 0.5 ºCelsius for the next few years.
This one-time event thereby managed to achieve what decades of political discussion about curbing CO₂ emissions has so far been unsuccessful at doing: counteracting the unprecedented global warming of our planet. Could Mount Pinatubo be pointing us to a viable new solution for climate change?
Many people, climate scientists included, are wary of proposals to reverse or reduce global warming by tinkering directly with Earth’s climate and atmosphere. Such efforts at geoengineering, they worry, could have unforeseen and dangerous regional side effects that we may not be able to control or reverse. What if it interferes with local patterns of rainfall – or produces powerful storms?
But after decades of getting nowhere with emissions caps, argues David Keith, we simply can no longer afford not to put these ideas on the table.
Keith is an applied physicist and climate scientist at Harvard, with dual appointments in the university’s schools of engineering and public policy. He splits his time between Cambridge and Calgary, where he runs Carbon Engineering – a company that works on developing technologies for the capture of carbon dioxide in the atmosphere and turning it into low-carbon fuel.
Keith dedicates both his academic and entrepreneurial efforts to the exploration of climate engineering. While his company works on methods to directly reduce the amount of CO₂ in the air, his research explores ways to counteract human contributions to rising CO₂ levels by diminishing the amount of solar energy that reaches Earth’s surface. Indeed, one method for this kind of Solar Radiation Management (SRM) takes a cue from Mount Pinatubo, and would involve the release of sulfate particles into the upper atmosphere:
Keith not only argues that we must seriously consider these options, but also suggests that they may not be as irreversible, costly, or dangerous as they seem.
There’s no question [solar radiation management] reduces the global average temperatures; even the people who hate it agree you could reduce average global temperatures. The question is: how does it do on a regional basis? By far the single most important thing to look at on a region-by-region basis is the impact on rainfall and temperature. And the answer is, it works a lot better than I expected. It’s really stunning. A lot of us thought that, in fact, geoengineering would do a lousy job on a regional basis – and there’s lots of talk on the inequalities – but in fact, when you actually look at the climate models, the results show they’re strikingly even.
Nevertheless, Keith by no means means to suggest humanity should begin experimenting with these methods immediately, nor should they be considered a viable and ethical alternative to cutting CO₂ emissions. Above all, he argues for thoughtful discussion, rigorous research, and global consensus about the best way forward. We must, above all, be patient and thorough. As he told Time Magazine in 02009, when the weekly named him a Hero of the Environment, “The thing about tools … is not that you have to use them: it’s that you have to understand them.”