Monday, October 1, 2012

Solar Geoengineering: Using Space Tech To Avert Climate Armageddon

After a summer without end, some climate researchers are again looking off-world for a way to geoengineer our way out of global warming.

Unlike geoengineering efforts to remove carbon dioxide and other greenhouse gases from earth itself, space-based Solar Radiation Management (SRM) would seek to literally deflect a small portion of the sun’s luminosity before it hits our atmosphere.

Ideas run the gamut — from placing permanent solar shields between the earth and sun; to creating a Saturn-like earth-orbiting ring of asteroidal dust that could act as a solar filter.

Earth-based SRM methods include increasing our planet’s natural atmospheric and ground-based reflectivity to avert solar radiation. Potential scenarios range from injecting sulfate particles into the stratosphere to literally painting rooftops and roads a “lighter shade of pale.”

For a reality check, turned to David Keith, a professor in the School of Engineering and the Kennedy School of Government at Harvard University, who has worked on climate geoengineering for over two decades.

How sanguine are you about current and future conventional efforts to control greenhouse gas emissions?

The last few decades of climate policy have been a phony war of bold exhortation and largely symbolic action. But looking a decade or two ahead, I remain optimistic that political interests will align sufficiently to allow enactment of economically-efficient policies to restrain emissions.

In lieu of CO2 removal engineering and climate change mitigation via fossil fuel emissions reduction, is SRM the obvious alternative?

It is important, but not “the” alternative. There are three fundamental options: cutting net emissions, adapting to climate change as it happens, and solar geoengineering by intervening in the climate system to reduce the impact of accumulated emissions. A combined strategy that uses all three gives us the best chance to limit climate impacts to people and the natural world. A strategy that focuses only on cutting emissions asks current generations to pay unrealistic amounts for the benefit of those living in the distant future. Advocates of climate policy have willfully disregarded both [climate change] adaptation and solar geoengineering in the hopes that a monomaniacal focus on emissions reduction would improve the chances of getting a political deal. It’s time for new thinking.

How long would SRM take to work?

The cooling effects of SRM would begin to make themselves felt the same day that such a system was “switched on”. But to deploy SRM responsibly, we want to start with a much broader scientific effort to understand its benefits and risks using both laboratory methods and micro-scale experiments. Only if those were successful, [would] we be in a position to begin a very gradual, carefully-monitored deployment to look for the unexpected. We should begin a serious broad-based SRM research effort today. It buys us a [climate mitigation] option.

How much solar radiation would need to be deflected to be effective?

There is no threshold. A tiny reduction in solar radiation would provide tiny benefits in the form of reduced climate change, and also a tiny risk of side effects. If we wanted to roughly undo the total temperature rise from today’s accumulation of greenhouse gases, we would need to scatter a about a percent of sunlight back into space. While technically possible, it would be crazy. SRM inhibits precipitation even more effectively than it cools the climate. A sensible plan would compensate [for] only a portion of the greenhouse gas-driven warming. The best strategies likely combine a reduction in greenhouse gas emissions, accelerated efforts to adapt to climate change and some SRM.

What advantages do space-based solar shields offer over earth-based solar radiation mitigation strategies?

A space-based system gets you out of environmental risks that come from actually putting a substance in the stratosphere. Some space-based systems might allow you to do more elaborate tailoring of the sun-shading effect, perhaps allowing more precise manipulation of climate. But I doubt that these advantages are enough to outweigh the cost and inflexibility disadvantages of space-based systems until well into the latter half of this century.

But is SRM really needed at this moment?
If we had a well-tested SRM system and some rough agreement among a handful of major powers, then I would vote to start SRM now. But I would want to start very gradually; to ramp it up over time in order to give us the best chance to learn about the technology and about how to govern it as we go.

How does SRM stack up against ground-based CO2 reduction scenarios in terms of overall efficiency and effectiveness?

Carbon removal and solar geoengineering are very different tools. Solar geoengineering acts quickly and could reduce the damaging impacts of climate change over a single generation, but it does nothing to slow the buildup of carbon dioxide in the atmosphere that is steadily increasing the danger of climate disruption. Cutting emissions of carbon dioxide is necessary to slow accumulation of carbon dioxide in the atmosphere, but because of the enormous inertia in the carbon cycle, even a concerted effort to cut emissions would not materially reduce the risks of climate change for many decades.

What are the projected results with the leading methods?

All SRM methods aim to reduce the amount of sunlight the earth absorbs by scattering some of the incoming light back to space. All of them suffer from the fundamental limitation that reducing sunlight is simply not the same as reducing the greenhouse gases that cause climate change. While SRM can limit climate change, it can only partially compensate for the environmental impacts of accumulating greenhouse gases. And all these methods are bound by the uncertainty in predicting how earth’s climate will react to reductions in sunlight.

What are some adverse SRM effects? Would we have to worry about unexpected changes in regional climate as a result?

There are risks that come from any specific SRM technology. Sulfates in the stratosphere, for example, can destroy ozone and they contribute to air pollution when then fall back to the lower atmosphere. Then there are problems that come from using a reduction in sunlight to reduce climate change driven by greenhouse gases. This compensation can never be perfect and there will be changes in local climate. But evidence to date suggests that at least for relatively small amounts of SRM, the compensation would work well.

What are the costs and deployment time-frames?

We just did an engineering study of the cost of transporting SRM materials to the stratosphere. It can be done using hardware that the could be procured off-the-shelf today, and the cost to produce a material impact on climate would be no more than $1 billion a year, a negligible amount in a global economy now over $60 trillion per year. The earliest that I can imagine it would make any sense to begin a very slow SRM deployment is a decade out.

What are the consequences of a failed SRM initiative?

It depends how it fails. The most plausible technical failure would be some unexpected and serious side-effect. If this happens early in a gradually-increasing deployment then the consequences would simply be that one would stop the program and manage the side-effects to the extent possible. Things get harder later on if the deployment is large-scale because then one must balance the sudden warming that would come from suddenly stopping against the newly discovered dangerous side-effect.

To your knowledge, has the U.S. government ever conducted atmospheric geoengineering to counter climate warming?

No. But there are some wild rumors out there. One sixth of respondents in a large public survey we ran in Canada, Britain and the U.S. believed that it was partially or completely true that “The government has a secret program that uses airplanes to put harmful chemicals into the air.” Such a program would have to involve thousands of people over decades, each knowing that they were conspiring against their fellow citizens. The idea that our government could keep such a secret is simply absurd.


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