The first experience of attenuating the sun will test a way to cool the Earth


Zhen Dai, Frank Keutsch and David Keith

Frank Keutsch, Zhen Dai and David Keith (left to right) in the Keutsch lab at Harvard University.Credit: Kayana Szymczak for Nature

Zhen Dai holds a small glass tube covered with a white powder: calcium carbonate, a ubiquitous compound used in all fields, from paper to cement, through toothpaste and cake mixes. Pour one tablet in water and you will get a gaseous antacid that will soothe the stomach. The question posed to Dai, Ph.D. candidate at Harvard University in Cambridge, Mass., And her colleagues is whether this harmless substance could also help humanity to relieve the ultimate case of Indigestion: global warming caused by pollution by greenhouse gases.

The idea is simple: spray a pile of particles into the stratosphere, which will cool the planet by sending some of the sun's rays back into space. Scientists have already witnessed the principle in action. During the eruption of Mount Pinatubo in the Philippines in 1991, about 20 million tons of sulfur dioxide were injected into the stratosphere, the atmospheric layer extending from about 10 to 50 kilometers to the above the surface of the Earth. The rash created a fog of sulphate particles that cooled the planet by about 0.5 ° C. For about 18 months, the average temperature of the Earth returned to what it was before the arrival of the steam engine.

The idea that humans could turn off the Earth's thermostat by similar artificial means is decades old. It fits into a broader class of global cooling patterns known as geoengineering, which have long generated intense debate and, in some cases, fear.

Researchers have largely limited their work on such tactics to computer models. Among the concerns, it is feared that the decline of the sun can turn around or at least strongly disadvantage certain areas of the world, for example by depriving crops of sunlight and changing the rain patterns.

However, as emissions continue to rise and weather forecasts remain alarming, discussions on geoengineering research are beginning to gain ground among scientists, policy makers and some environmentalists. This is because many researchers have come to the alarming conclusion that the only way to prevent the serious effects of global warming will be either to suck huge amounts of carbon dioxide from the atmosphere or to artificially cool the atmosphere. planet. Or maybe more likely, both.

If all goes well, the Harvard team will be the first in the world to move solar geoengineering from the lab to the stratosphere, with a project called Stratospheric Controlled Disturbance Experiment (SCoPEx). The first phase – a US $ 3 million test involving two flights of a dirigible balloon located 20 kilometers above the southwestern United States – could be launched as early as the first half of 2019. Once in place, the experiment would release small feathers of calcium carbonate, about 100 grams each, which roughly corresponds to the amount found in an average bottle of antacid commercially available. The balloon would then turn around to observe the dispersion of the particles.

The test itself is extremely modest. Dai, whose PhD work over the last four years has been to build a tabletop device to simulate and measure chemical reactions in the stratosphere prior to the experiment, does not dwell on the concerns raised by such research. "I'm studying a chemical," she says. "It's not like it's a nuclear bomb."

Nevertheless, the experience will be the first to fly under the banner of solar geoengineering. That's why we're watching the situation closely, especially from environmental groups who say that such efforts divert attention away from the only permanent solution to climate change: reducing greenhouse gas emissions. Greenhouse. According to Jim Thomas, co-executive director of ETC Group, an environmental defense organization based in Val-David, near Montreal, Canada, the scientific results of SCoPEx do not matter. "It's also an experience of changing social norms and crossing a line as it is a scientific experiment. "

Conscious of this attention, the team is slowly moving forward and working to put in place a clear oversight of the experience, in the form of an external advisory committee to review the project. Some say that such a framework, which could pave the way for future experiments, is even more important than the results of this test alone. "SCoPEx is the first to get out of the door, and it is triggering an important discussion about what should be independent advice, guidance and monitoring," said Peter Frumhoff, head of climate research at the University of California. Union of Concerned Scientists of Cambridge, Massachusetts. member of an independent group to select the chair of the advisory committee. "Doing things right is much more important than doing it quickly."

Joining forces

In many ways, the stratosphere is a great place to try to make the atmosphere more reflective. The small particles that are injected can spread around the world and stay in the air for two years or more. If placed strategically and evenly in both hemispheres, they could create a relatively uniform coverage that would protect the entire planet (see "Global Response"). The process does not have to be very expensive; In a report released last month, the Intergovernmental Panel on Climate Change suggested that a fleet of aircraft flying at high altitude could deposit enough sulfur to offset warming. about 1.5 ° C at a cost of between $ 1 and $ 10 billion a year.1.

Paul Jackman /Nature

Most of the research in solar geoengineering has so far concentrated on sulfur dioxide, the same substance emitted by Mount Pinatubo. But sulfur might not be the best candidate. In addition to cooling the planet, the aerosols generated during this eruption have accelerated the rate at which chlorofluorocarbons deplete the ozone layer, which protects the planet from the sun's harmful ultraviolet rays. Sulfate aerosols are also warmed by the sun, which is enough to affect the movement of moisture and even on the jet. "We do not fully understand all of these downstream effects," says Frank Keutsch, Harvard Atmospheric Chemist and SCoPEx's lead investigator.

The first stratospheric experiments of the SCoPEx team will focus on calcium carbonate, which is expected to absorb less heat than sulphates and have less impact on ozone. But the manual answers – and even the Dai table feature – can not capture the complete picture. "In reality, we do not know what it would do because it does not exist in the stratosphere," says Keutsch. "This sets up a red flag."

SCoPEx aims to gather real data to solve this problem. The experiment began as a partnership between Harvard atmospheric chemist James Anderson and experimental physicist David Keith, who joined the university in 2011. Keith has been studying intermittent geoengineering options for over 25 years. years. In 2009, while he was at the University of Calgary in Canada, he founded the Carbon Engineering company in Squamish, which works to commercialize a technology to eliminate the carbon dioxide from the atmosphere. After joining Harvard, Keith used the research funds he had received from the Bill & Melinda Gates Foundation in Seattle, Washington, to begin planning the experiment.

Keutsch, who was involved later, is not a climatologist, but is at best a reluctant geo-engineer. But he is concerned about the direction of humanity and what it means for the future of its children. When he saw Keith talk about the idea of ​​SCoPEx at a conference after starting at Harvard in 2015, he said his initial reaction was that the idea was "totally crazy." ". Then he decided that it was time to engage. "I asked myself, an atmospheric chemist, what can I do?" He has partnered with Keith and Anderson and has since taken the lead in experimental work.

An eye on the sky

SCoPEx has already made progress with previous solar geoengineering efforts. The UK experiment on stratospheric particle injection for climate engineering, which was aimed at spraying water 1 kilometer into the atmosphere, was canceled in 2012 partly because scientists had applied for a patent on a device that can affect all human beings on the planet. (Keith says that there will be no patent on the technologies involved in the SCoPEx project.) And the US researchers of the Marine Cloud Brightening project, which aims to spray saltwater droplets into the lower atmosphere to increase the reflectivity of ocean clouds, have tried to raise funds for the project for nearly ten years.

Climatic chamber to test the instruments used in the SCoPEx field mission

A climate chamber to test the instruments used in the SCoPEx field mission.Credit: Kayana Szymczak for Nature

Although SCoPEx may be the first solar geo-engineering experiment to fly, Keith explains that other projects that have not seen themselves as such have already provided useful data. In 2011, for example, the experience of aerosol clouds emitted in the eastern Pacific pumped smoke into the lower atmosphere to mimic ship pollution, which can cause lightening clouds by capturing more water vapor. The test was used to study the effect on marine clouds, but the results had a direct impact on geoengineering: the brighter clouds produced a 50-fold cooling effect compared to researcher's ships carbon2.

Keith says the Harvard team has not yet met with public protest or direct opposition, aside from an occasional conspiracy theorist. The researchers, he adds, have more to deal with the fear of science funding agencies to invest in geo-engineering to spark protests from environmentalists.

To advance the field, Keith set a target in 2016 of raising $ 20 million to fund an official research program covering not only experimental work, but also modeling, governance and research research. 39; ethics. To date, he has raised approximately $ 12 million, primarily from the Gates Foundation and other philanthropists; the pot provides funds to dozens of people, mostly part-time.

Keith and Keutsch also want an external advisory committee to review SCoPEx before it takes off. The committee, which has not yet been selected, will report to the Dean of Engineering and Vice President of Research at Harvard. "We consider this to be part of a process to generate broader support for research on this topic," said Keith.

Keutsch is looking forward to the advice of an external group and hopes that he will be able to clarify how tests like his should unfold. "It's a much harder political experience than I expected," he says. "I was a little naive."

SCoPEx also faces technical challenges. We must spray particles of the right size: the team calculates that those with a diameter of about 0.5 micrometer should disperse and reflect the sunlight well. The ball must also be able to reverse its trajectory in the air to cross its own wake. Assuming that the team is able to find the calcium carbonate plume – and this is not guaranteed – SCoPEx needs instruments that can analyze particles and bring samples back to Earth.

"It will be a difficult experience, and it may not work," said David Fahey, an atmospheric scientist with the National Oceanic and Atmospheric Administration in Boulder, Colorado. In the hope, the Fahey team has equipped SCoPEx with a lightweight instrument that can reliably measure the size and number of particles released. The balloon will also be equipped with a laser device capable of monitoring the plume from afar. Other equipment likely to collect information on the level of moisture and ozone in the stratosphere could also fly on the balloon.

Up to the stratosphere

Keutsch and Keith are still working on some technical details. Plans with a balloon company have failed, so they are now working with a second. And a team of independent engineers in California is working on options for the sprayer. For simplicity, the SCoPEx group plans to fly the balloon in the spring or fall, when the stratospheric winds change direction and – for a brief period – calm down, which will facilitate plume tracking.

For all these reasons, Keutsch describes the first flight as an engineering test, intended primarily to demonstrate that everything works as it should. The team is ready to spray particles of calcium carbonate, but could use salt water to test the sprayer if the advisory committee opposes it.

Keith still thinks that sulphate aerosols may ultimately be the best choice for solar geoengineering, if only because so much research has been done on their impact. He added that the possibility that sulphates reinforce the depletion of the ozone layer should become less of a concern in the future, given that efforts to restore the ozone layer through to the reduction of pollutants continue. Nevertheless, his main hope is to set up an experimental program in which scientists can explore different aspects of solar geoengineering.

There are many outstanding issues. Some researchers have suggested that solar geoengineering could alter rainfall patterns and even lead to more droughts in some areas. Others warn that one of the possible benefits of solar geoengineering – maintaining crop yields by protecting them from heat stress – may not materialize. In a study published in August, researchers found that yields of corn (maize), soy, rice and wheat3 After two volcanic eruptions, Mount Pinatubo in 1991 and El Chichón in Mexico in 1982 darkened the sky. Such reductions may be sufficient to offset potential future gains.

According to Keith, scientific knowledge suggests that the benefits may well outweigh the potential negative consequences, particularly in a world in which warming is not controlled. The common disadvantage is that protecting the sun does not affect emissions, so greenhouse gas levels will continue to rise and the ocean becomes even more acidic. But he suggests that solar geoengineering could reduce the amount of carbon that would otherwise be found in the atmosphere, including minimizing permafrost loss, promoting forest growth and reducing the need for cooling buildings. In an unpublished analysis of rainfall and extreme temperatures using a high resolution climate model, Keith and others found that almost every region of the world would benefit from a moderate solar geoengineering program. "Despite all the concerns, we can not find any area that would be really worse," he says. "If solar geoengineering is as good as these models show, it would be crazy not to take it seriously."

There is still widespread uncertainty about the state of science and assumptions in the models, including the idea that humanity could unite to establish, maintain and finally dismantle a well-designed geoengineering program while tackling the underlying problem of emissions. Nevertheless, important organizations, including the Royal Society of the United Kingdom and the US National Academies of Science, Engineering and Medicine, have called for more research. In October, the academies launched a project that will attempt to provide a blueprint for such a program.

Some organizations are already trying to promote discussions between policy makers and government officials at the international level. The governance initiative for the management of solar radiation organizes for example workshops in the countries of the south of the planet. And Janos Pasztor, Climate Officer of former UN Secretary-General Ban Ki-moon, has spoken with senior government officials from around the world as part of his leadership role. Carnegie Climate Geoengineering Governance Initiative, a non-profit organization. At New York. "Governments need to participate in this discussion and understand these issues," Pasztor said. "They need to understand the risks – not just the risks, but the risks of not understanding and not knowing."

One of the concerns is that governments may one day panic over the consequences of global warming and engage in a random program of solar geoengineering, an undeniable possibility given that the costs are cheap enough for many countries, and perhaps even a few individuals, can afford. to go alone. These and other issues were raised earlier this month in Quito, Ecuador, at the annual Montreal Protocol Summit, which regulates chemicals that damage the stratospheric ozone layer. Several countries called for a scientific assessment of the potential effects of solar geoengineering on the ozone layer and, more generally, on the stratosphere.

If the world is really concerned about geoengineering, Fahey says researchers could conduct many sophisticated experiments using high altitude satellites and planes. But for the moment, he says, SCoPEx will be useful, if only because it moves the conversation forward. "Do not talk about geoengineering is the biggest mistake we can make right now."


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