The first sun-darkening experiment 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) at Keutsch's laboratory at Harvard University.Credit: Kayana Szymczak Nature

Zhen Dai holds a small glass tube coated with a white powder: calcium carbonate, a ubiquitous compound used in everything from paper and cement to toothpaste and cake mixes. Put a tablet in the water and the result is an effervescent antacid that soothes the stomach. The question for Dai, a doctoral candidate at Harvard University in Cambridge, Mass., And his colleagues is whether this innocuous substance could also help humanity alleviate the latest case of indigestion: global warming caused by pollution from greenhouse gases .

The idea is simple: to spray a bunch of particles in the stratosphere and they will cool the planet by reflecting some of the sun's rays back into space. Scientists have already witnessed the principle in action. When Mount Pinatubo erupted in the Philippines in 1991, it injected about 20 million tons of sulfur dioxide into the stratosphere – the atmospheric layer stretching 10 to 50 kilometers above the Earth's surface. The eruption created a haze of sulphate particles that cooled the planet to about 0.5 ° C. For about 18 months, Earth's average temperature returned to what it was before the steam engine arrived.

The idea that humans can refuse the earth's thermostat in a similar and artificial way is decades. It fits into a broader class of planetary cooling schemes known as geoengineering, which have long generated intense debate and, in some cases, fear.

Researchers have largely restricted their work in such tactics to computer models. Among the concerns is the fact that the sun's darkening can backfire, or at least strongly hinder some areas of the world, for example by stealing the plantings of sunlight and changing the patterns of rain.

But as emissions continue to rise and climate projections remain dire, talks on geoengineering research are starting to gain more momentum among scientists, policymakers and some environmentalists. This is because many researchers have come to the alarming conclusion that the only way to avoid the severe impacts of global warming is to extract large amounts of carbon dioxide from the atmosphere or to artificially cool the planet. Or, perhaps more probably, both.

If all goes as planned, the Harvard team will be the first in the world to move solar geoengineering out of the laboratory and into the stratosphere with a project called the Stratosphere Controlled Disruption Experiment (SCoPEx). The first phase – a $ 3 million test involving two flights of an airship balloon 20 kilometers above the southwestern United States – could be launched in the first half of 2019. Once in place, the experiment would release small feathers of calcium carbonate each about 100 grams, approximately equivalent to the amount found in an average bottle of marketed antacid. The balloon would then turn to watch the particles disperse.

The test itself is extremely modest. Dai, whose doctoral work in the last four years has involved the construction of a tabletop device to simulate and measure chemical reactions in the stratosphere before the experiment, does not emphasize concerns about this research. "I'm studying a chemical," she says. "It's not like it's a nuclear bomb."

However, the experiment will be the first to fly under the banner of solar geoengineering. And so it is under intense scrutiny, including some environmental groups, who say such efforts are a dangerous distraction from being the only permanent solution to climate change: reducing greenhouse gas emissions. The scientific outcome of SCoPEx does not really matter, says Jim Thomas, co-executive director of the ETC Group, an environmental defense organization in Val-David, near Montreal, Canada, which opposes geoengineering: "This is both a change social norms and cross a line as it is a scientific experiment. "

Aware of this attention, the team is moving slowly and is working to establish clear oversight of the experiment in the form of an external advisory committee to review the project. Some say that such a structure, which could pave the way for future experiments, is even more important than the results of this test. "SCoPEx is the first to be released, and it's triggering a major conversation about how independent guidance, advice and supervision should be," says Peter Frumhoff, chief climate scientist at the Union of Concerned Scientists in Cambridge, Mass., And a member of an independent panel that was tasked with selecting the head of the advisory committee. "Getting it right is much more important than doing it quickly."

Joining forces

In many ways, the stratosphere is an ideal place to try to make the atmosphere more reflective. Small particles injected there may spread through the globe and remain in the air for two years or more. If placed strategically and regularly in both hemispheres, they could create a relatively uniform blanket that would protect the entire planet (see "Global Intervention"). The process does not have to be very expensive; In a report last month, the Intergovernmental Panel on Climate Change suggested that a fleet of high-range aircraft could deposit enough sulfur to compensate for about 1.5 ° C of heating by about $ 1 billion to $ 10 billion per year.1.

Paul Jackman /Nature

Most of the research in solar geoengineering so far has focused on sulfur dioxide, the same substance released by Mount Pinatubo. But sulfur may not be the best candidate. In addition to cooling the planet, the aerosols generated in that eruption have accelerated the rate at which chlorofluorocarbons deplete the ozone layer, which protects the planet from the sun's harmful ultraviolet radiation. Sulphate aerosols are also heated by the Sun, enough to potentially affect the movement of moisture and even change the jet stream. "There are all those downstream effects that we do not fully understand," says Frank Keutsch, an atmospheric chemist with Harvard's principal investigator and SCoPEx.

The initial stratospheric experiments of the SCoPEx team will focus on calcium carbonate, which should absorb less heat than sulfates and have less impact on ozone. But the answers in the textbooks – and even Dai's desk device – fail to capture the full picture. "In fact, we do not know what that would do, because it does not exist in the stratosphere," says Keutsch. "This sets up a red flag."

SCoPEx aims to collect real-world data to solve this. The experiment began as a partnership between atmospheric chemist James Anderson of Harvard and experimental physicist David Keith who moved to university in 2011. Keith has been researching a variety of geoengineering options for over 25 years. In 2009, while at the University of Calgary, Canada, he founded Carbon Engineering in Squamish, which is working to commercialize technology to remove carbon dioxide from the atmosphere. After joining Harvard, Keith used research funding he received from the Bill & Melinda Gates Foundation in Seattle, Washington, to begin planning the experiment.

Keutsch, who later became involved, is not a climate scientist and, at best, is a reluctant geo-engineer. But he worries about the direction of mankind and what it means for the future of their children. When he saw Keith talk about the SCoPEx idea at a conference after starting at Harvard in 2015, he said his initial reaction was that the idea was "totally insane". So he decided it was time to get involved. "I wondered, an atmospheric chemist, what can I do?" He joined forces with Keith and Anderson, and has since taken the lead in experimental work.

An eye in the sky

SCoPEx has already advanced more than previous efforts in solar geoengineering. The British experience of injecting stratospheric particles into climate engineering, which sought to spray water within 1 km of the atmosphere, was canceled in 2012, in part because scientists applied for patents for a device that could affect all humans on the planet. (Keith says there will be no patents on any technology involved in the SCoPEx project.) And US researchers with the Marine Cloud Brightening Project, which aims to spray salty water droplets in the lower atmosphere to raise the reflectivity of ocean clouds, have been trying to raise money for the project for almost a decade.

Environmental chamber to test instruments used in SCoPEx field mission

An environmental chamber to test instruments used in the SCoPEx field mission.Credit: Kayana Szymczak Nature

Although SCoPEx may be the first solar geoengineering experiment to fly, Keith says other projects that have not identified themselves as such have provided useful data. In 2011, for example, the Eastern Pacific Issued Aerosol Cloud Experiment pumped smoke into the lower atmosphere to mimic ship pollution, which can cause clouds to glow, capturing more water vapor. The test was used to study the effect on marine clouds, but the results had a direct impact on the science of geoengineering: the brightest clouds produced a cooling effect 50 times greater than the heating effect of researchers' ship carbon emissions .2.

Keith says the Harvard team has yet to find public protests or any direct opposition – other than the occasional conspiracy theorist. The challenge faced by researchers, he says, stems more from the fear among scientific funding agencies that investing in geoengineering leads to protests from environmentalists.

To help advance the field, Keith set a goal of $ 20 million to support a formal research program covering not only experimental work but also modeling, governance, and ethics research in 2016. He has raised about $ 12 million so far, mostly from the Gates Foundation and other philanthropies; the pot provides funding for dozens of people, largely on a part-time basis.

Keith and Keutsch also want an external advisory committee to review SCoPEx before it flies. The committee, which will still be selected, will report back to the dean of engineering and deputy dean of research at Harvard. "We see this as part of a process to build broader support for research on this subject," says Keith.

Keutsch is eager to have the guidance of an outside group, and hopes he can clarify how tests like his should be done. "This is a far more politically challenging experiment than I expected," he says. "I was a little naive."

SCoPEx also faces technical challenges. It should spray particles of the right size: the team estimates that those with a diameter of about 0.5 micrometers should disperse and reflect well in the sunlight. The balloon should also be able to reverse its course in the rarefied air, so that it can pass through its own trace. Assuming the team is able to find the calcium carbonate pen – and there is no guarantee they can – SCoPEx needs instruments that can analyze the particles and, hopefully, take the samples back to Earth.

"It's going to be a difficult experience, and it may not work," says David Fahey, an atmospheric scientist at the National Oceanic and Atmospheric Administration in Boulder, Colo. Hoping that this will happen, Fahey's team provided SCoPEx with a lightweight instrument that can safely measure the size and number of particles released. The balloon will also be equipped with a laser device that can monitor the pen from far away. Other equipment that could collect information about the level of moisture and ozone in the stratosphere could also fly over the balloon.

Even the stratosphere

Keutsch and Keith are still working on some technical details. Plans with a balloon company have fallen, so they are now working with a second. And an independent team of engineers in California is working on options for the sprayer. To simplify things, the SCoPEx group plans to fly the balloon in the spring or fall, when stratospheric winds change direction and – for a brief period – calm down, which will make it easier to trace the pen.

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

Keith still thinks sulphate aerosols may be the best choice for solar geoengineering, even as there has been more research on their impact. He says the possibility of sulfates increasing ozone depletion should become a minor concern in the future, as efforts to restore the ozone layer through pollutant reductions continue. However, their main hope is to establish 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 precipitation patterns and even lead to more droughts in some regions. Others warn that one of the potential benefits of solar geoengineering – keeping crop yields safe from heat stress – may not materialize. In a study published in August, researchers found that yields of corn, soybeans, rice and wheat3 After two volcanic eruptions, Mount Pinatubo in 1991 and El Chichón in Mexico in 1982 obscured the skies. Such reductions may be sufficient to void any potential gains in the future.

Keith says that science so far suggests that the benefits could outweigh the possible negative consequences, particularly in comparison to a world where warming is not controlled. The commonly cited disadvantage is that sun protection does not affect emissions, so greenhouse gas levels will continue to rise and the ocean will become even more acidic. But he suggests that solar geoengineering could reduce the amount of carbon that would otherwise end up in the atmosphere, including minimizing the loss of permafrost, promoting forest growth, and reducing the need to cool buildings. In an unpublished analysis of extremes of precipitation and temperature using a high-resolution climate model, Keith and others found that almost all regions of the world would benefit from a moderate solar geoengineering program. "Despite all the worries, we can not find areas that are worse off," he says. "If solar geoengineering is as good as the one shown on these models, it would be crazy not to take it seriously."

There is still widespread uncertainty about the state of science and the assumptions in the models – including the idea that humanity could come together to establish, maintain, and eventually dismantle a well-designed geoengineering program while addressing the underlying problem emissions. Still, prominent organizations, including the Royal Society of the United Kingdom and the National Academies of Science, Engineering and Medicine of the USA, asked for more research. In October, the academies launched a project that will attempt to provide a model for this program.

Some organizations are already trying to promote discussions among policymakers and government officials at the international level. The Solar Radiation Management Governance Initiative is running workshops throughout the global south, for example. And Janos Pasztor, who has dealt with climate issues under former UN Secretary-General Ban Ki-moon, has spoken with senior government officials around the world as head of the Carnegie Climate Geoengineering Governance Initiative, a nonprofit organization. In New York. "Governments need to engage in this discussion and understand these issues," says Pasztor. "They need to understand the risks – not only the risks of doing so, but also the risks of not understanding and not knowing."

One concern is that governments may someday panic at the consequences of global warming and move forward with a random solar geoengineering program, a distinct possibility, as costs are cheap enough that many countries, and perhaps even some individuals, can afford. to go it alone. These and other issues surfaced earlier this month in Quito, Ecuador, at the annual Montreal Protocol summit, which regulates chemicals that deplete the stratospheric ozone layer. Several countries called for a scientific assessment of the potential effects that solar geoengineering could have on the ozone layer and the stratosphere more widely.

If the world takes geoengineering seriously, Fahey says there are many sophisticated experiments that researchers could do using satellites and high-altitude airplanes. But for now, he says, SCoPEx will be valuable – at least because it drives the conversation. "Not talking about geoengineering is the biggest mistake we can make right now."


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