(Credit: kazuend/Unsplash) Catastrophic climate change seems inevitable. Between the still-accelerating pace of greenhouse gas emissions and the voices of global warming deniers, hitting the targets laid out in the Paris Accord to slow the pace of a warming climate feels increasingly elusive. To hit even the 2 degree Celsius cap on a global temperature increase, emissions would need to peak in 2020, or less than three years from now, and keep going down after that. We could do it, but will we? If we can't change our behavior, perhaps there's another way to control our climatic destiny. One that's received a lot of attention recently is geoengineering, or somehow deploying technology to compensate for the effects of carbon dioxide and other greenhouse gases and bend the climate to our will. Climate scientists as far back as the 1960s have been proposing ways to counteract the effects of greenhouse gases in our atmosphere to mitigate the consequences of climate change. Some are fairly ludicrous, others are quite feasible. But letting these planet-wide fixes loose on the world could wreak more havoc than they prevent, scientists worry. And the nightmare scenarios range anywhere from large-scale famine to international warfare. The tension at the heart of the debate is that we may not have a choice. Warming may reach a point where even potentially dangerous solutions seem feasible, and if that time comes, well, perhaps we should have some options handy.

Simple Math

One approach is to suck CO2 out of the air faster than we're putting it in. Some projects have reported initial success removing carbon from the air and sequestering it in rocks or as a supercritical fluid, but there's no sign they'll scale up meaningfully any time soon. Plants, Mother Nature's own carbon scrubbers, are another option, but to achieve carbon neutrality, we'd need to plant enough new forests to cover 15 percent of the world's productive land or cede nearly 10 percent of the ocean's surface to seaweed farms . The other option is to stop some of the sun's rays from penetrating the atmosphere, or at least bounce them back out. Some groups have proposed planting lighter crops and painting surfaces white (like some of Los Angeles' streets) to reduce heat absorption, while others have gone so far as to suggest giant mirrors in space. Those techniques could help, but many researchers focus on the very thing that's causing so much trouble in the first place: the atmosphere. If you look at a record of global temperature, you'll notice that it's far from linear. The trend whiplashes up and down for various reasons, but scientists know what's behind some of the sharpest drops: volcanoes. Along with ash and fire, volcanoes also belch large quantities of sulfur dioxide, where it hangs around in the atmosphere as a fine spray of liquid particles known as an aerosol. These aerosols make the Earth's atmosphere a bit more opaque and reflect some of the incoming light, creating a cooling effect. When Mt. Pinatubo erupted in 1991, it spewed some 20 million metric tons of sulfur dioxide into the atmosphere. The massive aerosol injection cooled large parts of the Earth by almost a full degree Fahrenheit on average over the course of the next year. Other large-scale eruptions have had similar effects, most notably the "Year Without a Summer," in 1816 following the eruption of Mount Tambora the previous year.

Cooling Clouds

Volcanic eruptions won't save us from climate change, but they do offer a compelling case study. Researchers have proposed seeding the atmosphere with sulfur aerosols ourselves — absent fiery eruptions — to create the same cooling effect. There's plenty of reason for caution, though. Volcanic eruptions, for one, can have terrible consequences for agriculture around the world. In 1816, crops failed across the East Coast, Europe and in Asia, accompanied by floods and a typhus outbreak. Over 100,000 people are estimated to have died as a result. Pushing that much sulfur into the atmosphere rapidly disrupts weather patterns, bringing torrential rains where none were before, drying up areas accustomed to regular downpours and drastically dropping temperatures in some regions. That's largely because volcanoes inject aerosols into the atmosphere all at once, causing sudden, volatile variations in climate. A responsible geoengineering solution, of course, would take it slow and steady. Some researchers have suggested that aerosol distribution could be accomplished by a fleet of jets ferrying loads of sulfur into the stratosphere year-round, spread out across the planet to avoid concentrating the effects in one place. The application needn't necessarily be all that far off, either. The U.S. currently has enough jets to carry out the flights, says Anthony Jones, a climate researcher at the University of Exeter. The technology to efficiently release the aerosol might take a few years to develop, but it is possible, he says. Cost estimates range from around one to $10 billion, less than what is currently spent globally on climate research and mitigation, and certainly less than what it will cost to cope with its effects. Sulfur, too, is easy to come by. It's a byproduct of fossil fuel production, and sulfur reserves number in the billions of tons — a mining company in Alberta is building an actual pyramid of the stuff that will dwarf those in Egypt.

Volcanoes cool the climate. Volcanoes will not solve climate change. (Credit: Richard van Wijngaarden/Unsplash) To lay the groundwork for just such a plan, a team from Harvard will soon send a sulfur-laden balloon into the stratosphere, where it will spray a fine mist of the particles covering an area one half-mile long and a football field wide. The plan calls for the balloon and its sensor-studded gondola to then dip back through the cloud and gather data on how the cloud disperses and the effects it has on the atmosphere. The goal is to find out how accurate our current climate models are and hopefully inform future attempts at a climate intervention. "If you look at every climate model simulation ever done with some reasonable amount of solar geoengineering, done in some kind of reasonable way, the total amount of climate change that’s produced is substantially reduced," says Ken Caldeira, an atmospheric scientist at the Carnegie Institution for Science. It's findings like these that have caught the eye of legislators. Jerry McNerney, a Democratic Representative from California recently introduced a bill that would task the National Academy of Sciences with investigating the potential benefits and pitfalls of attempting a geoengineering solution to climate change. Though it wouldn't mean we're necessarily going ahead with it, it's a step in that direction. Secretary of State Rex Tillerson and other members of the Trump administration appear to be on board as well. Tillerson, who has denied that global warming is caused by humans in the past, described climate change as simply an "engineering problem."

So, We're Saved?

There's a compelling argument for cooling the climate, and the logistics of doing so work out. But researchers studying geoengineering are hardly optimistic. “No, absolutely not," says Jones of applying geoengineering to the world at large. "If you ask me today to vote whether we should geoengineer, or never, ever do it, I would be on the never, ever side," says Gernot Wagner, co-director of Harvard's Solar Geoengineering Research Program. Caldeira also spoke out strongly against applying geoengineering techniques today or in the future, even as he acknowledges that it would likely cool the climate. There are several reasons for taking this position. The first is that sulfur aerosols, or whatever we might choose to deploy, aren't the opposite of CO2. They can counteract some of the symptoms of producing excess greenhouse gases, but there will be other effects as well. This kind of geoengineering, for example, won't stop the acidification of the oceans. It's also a long-term commitment: If we stopped pumping sulfur into the atmosphere, the climate would snap right back to where it was before. Sulfur aerosols would also change the climate in a different way than greenhouse gases do, says Peter Irvine, a postdoctoral researcher at Harvard specializing in climate modeling. Because they reflect sunlight, as opposed to trapping heat like CO2 does, aerosols would over-cool the tropics and under-cool the poles, again throwing off global weather patterns with unpredictable results. In addition, sulfur aerosols have relatively greater effects on rainfall than does CO2. Totally compensating for the warming from CO2 would overcorrect the hydrological cycle, leading to weaker monsoons in Southeast Asia, and less rainfall overall. On top of it all, this is all just conjecture at this point—educated conjecture, to be fair. We just aren't well-informed enough to be climate engineers. "We simply don't know enough to pull the trigger now," Wagner says. "What we must do now is do the research. And frankly, the list of potential questions is very, very long."

These are clouds. They live in the atmosphere. (Credit: Tom Barrett/Unsplash) Regardless, as some nations begin to feel the effects of climate change more than others, they could decide to undertake some form of climate control in their own region without considering what it would mean for the rest of the world. Jones gets at the issue in a recent paper in Nature Communications, where he and his team examine the effects of releasing a sulfur aerosol, or something similar, in just one hemisphere. In short, it would be bad. Releasing aerosols in the northern hemisphere could potentially suppress tropical cyclones and move the intertropical convergence zone, a band of intense rainfall that fuels monsoons critical to agriculture in the tropics. Doing the same thing in the southern hemisphere would have the opposite effect. Each could be potentially destructive to the millions of people living near the equator. The outcome of irresponsible geoengineering could be international conflict, researchers have warned, as nations retaliate for weather-related provocations. Irvine, though, is less worried about climate wars. "If a nation is acting in its own selfish interest, what benefits would they get from pissing of the entire tropics, pissing off the entire world for the sake of a slight change in climate in their favor?" he asks. Even if China were to go ahead and bomb the stratosphere with sulfur, Irvine says, they would probably do it in a way that affected the entire world equally, lessening the risk of famines and conflict. Ramping up aerosol loading slowly — say 1 percent of Mt. Pinatubo's sulfur emissions this year, two the next, and so on — would probably be sufficient to slowly and evenly cool the planet, he thinks, based on our current models.

Gift or Threat?

Still, beyond the quantitative qualms about geoengineering's effects, there's an altogether more human concern. It's based on behavioral economics, and it's called a moral hazard. The basic idea is that when we feel that we're protected, we're more likely to take risks. A simple analogy is someone who drives recklessly once they put on a seatbelt, confident that they'll be saved in the event of a wreck. But it's a false sense of security; dutiful seatbelt-wearers die in crashes every year. With geoengineering, the logic is the same. If we see scientists taking steps to save us, we may stop worrying about putting CO2 into the atmosphere. Even if we had, in Caldeira's words, "a benevolent dictator of the world," who could geoengineer responsibly, it's just not a fix for climate change. At the end of the day, we'll still be pumping CO2 into the atmosphere, and sulfur will only cover it up. Geoengineering, in other words, will just kick the climate can down the road a bit. And this is where climate scientists have struck an uneasy bargain with the looming prospect of climate engineering. Despite their vocal concern, climate change is too pressing an issue, and geoengineering so tempting a fix, that it's likely been a foregone conclusion for some time. "Will somebody, somewhere, try things? That’s a yes, within 50 or 100 years," Wagner says. "Will it happen as part of a semi-rational climate policy globally coordinated? That’s a bigger question." Caldeira is more blunt. "If it’s really going to be used in this sort of emergency climate catastrophe scenario, then you’re not going to have that chance to learn about things going into it, so you pretty damn well better do the research up front," he says. If you need any more convincing, just think back to Pandora and her infamous box. Geoengineering may be a gift to humanity, but that doesn't necessarily mean we should open it.