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The Climate Scientist Who Pioneered Geoengineering Fears It's About to Blow Up

And Ken Caldeira, the climate scientist who pioneered the research, fears its time is coming.
Mount Pinatubo, erupting. Image: CVO Photo Archives, Wikimedia Commons

For years, Dr. Ken Caldeira's interest in planet hacking made him a curious outlier in his field. A highly respected atmospheric scientist, he also describes himself as a "reluctant advocate" of researching solar geoengineering—that is, large-scale efforts to artificially manage the amount of sunlight entering the atmosphere, in order to cool off the globe.

Caldeira says he's "less of a catastrophist than most," but he's worried that humans won't stop burning fossil fuels, and that the subsequent global warming will ultimately melt the ice caps and render vast swaths of the tropics unsuitable for growing crops. In the face of a climate emergency, he says, we may be able to temporarily limit the damage by, essentially, simulating a safer version of a massive volcanic eruption.


"By the end of the century, through most of the tropics, every summer temperature will be hotter than the hottest temperature yet on record, in most places," Caldeira told me.

The scientist, who toils for the Carnegie Institution Department of Global Ecology at Stanford University, was sporting jeans, a blazer, and a crop of unruly graying hair, and had traveled to the first major geoengineering conference in Berlin, to participate as a featured speaker.

"So the idea that huge swaths of the tropics might not be suitable for growing crops," he went on, "is plausible. And if you're unable to grow crops in huge swaths of the tropics, is that going to create political turmoil and migration? It could be a major disruption."

That, he says, is the likeliest reason we would see geoengineering attempted, and why we have to be prepared if politicians and increasingly desperate nations look for a quick climate fix. In a pair of interviews at the controversy-filled meeting, Caldeira offered his views on how and why we might come to live on a geoengineered planet, how the field is rapidly growing (and why that's dangerous), and what the odds are that humans will try to hijack the Earth's thermostat.

Our bias was to try to show that it wouldn't work, but every simulation we did showed it would work

Over the last decade, Caldeira and his colleagues have harnessed intricate models to examine the effect that blocking a small percentage of the sunlight that enters the Earth's atmosphere would have on the global climate.


Typically, a feat of geoengineering that could achieve an outcome like that involves injecting a bunch of tiny particles into the stratosphere; emulating, essentially, the global cooling effect of a major volcanic eruption like the one that blanketed the Philippines in lava and ash in 1991.

The eruption of Mt. Pinatubo blasted out 20 million tons of sulfur dioxide, leaving a slew of tiny particles hovering in the sky. All those aerosols lingered in the atmosphere, where they bounced more sunlight back into space than usual, spurring global temperatures to fall by nearly an entire degree Fahrenheit in subsequent years.

That event, the biggest of its kind in recent history, and thus best-suited for careful scientific study, eventually came to provide the template for solar geoengineering. Now, scientists consider spreading sulfate aerosols into the stratosphere (without any of mercury or other toxic stuff that volcanoes also tend to belch out), either with a fleet of planes, giant balloons, or even artillery to be perhaps the most plausible geoenginering proposal. Since the particulates only stay airborne temporarily, this would have to be done regularly, perhaps even annually.

Caldeira, at Stanford University

Caldeira published his first paper on climate hacking back in 2000. Originally, he says, he carried out the modeling experiments to prove that the concept was a nonstarter.

"Our philosophical bias was to try to show that it wouldn't work, but every simulation we did showed it would work," the affable and talkative Caldeira, frequenting an easy but weary smile, told me at the conference last week. "So I kind of became a reluctant advocate of at least doing the research."


"I'm one of the few people to become expert on the things I don't really like."

The initial experiments showed that a small amount of aerosols could indeed cool the planet enough to offset warming, while inflicting few obvious woes on the environment.

"We did a series of other papers," Caldeira says, "because people said, 'Oh, turning down the sun will hurt the plants and the land biosphere.' So we did another simulation and it turned out the land biosphere grew better, because, as seen after Mt. Pinatubo, the diffuse radiation brought more light down to lower leaves for the plant canopies, so you're getting the C02 fertilization without the heat stress. So the plants grew better."

With each new finding, it seemed, solar geoengineering appeared more feasible, and a less dangerous way to at least limit the rising temperatures caused by the growing concentration of carbon dioxide in the air.

"For the current generation of climate models, and the way people measure climate damage… at modest levels of solar geoengineering, everyone is better off than without it."

To reiterate: Caldeira's models show that if climate change continues, everyone, from the poor nations in the tropics, to the rich ones in the Northern Hemisphere, would reap benefits—more productive crops, less sweltering temperatures—from a simulated volcanic eruption.

He'll be the first to point out that there are plenty of attendant social and political problems with the idea, and grave dangers of coming to rely on the technology. For instance, if we were to pull the plug after starting a geoengineering program, it could catapult the planet into even worse levels of warming. It does nothing to address global warming's ugly twin brother, ocean acidification. And by presenting the world's public with an apparent techno-fix, it could deflate the movement to reduce carbon emissions.


"For me, my main concern is that we would start doing solar geoengineering while we're still building things with smokestacks and tailpipes," he tells me. "And in that framing, I think the solar geoengineering is just facilitating continued greenhouse gas emissions."

But the technology itself isn't the hurdle.

I think that there's at least a 10-20-30 percent chance that we're eventually going to do it

"We know volcanoes cool the planet, we know it basically works," Caldeira says. "The studies show that not that much stuff can produce a dramatic cooling, that it just seems to be the most obvious thing with enough leverage."

"And also the masses of material involved are thought to be reasonable," he adds.

By that, he means it wouldn't be too daunting a logistical task; and, it'd be relatively cheap. He points me to a study published in Environmental Research Lettersby researchers from Aurora Flight Strategies, that suggested that this kind of geoengineering could be accomplished for $5 billion a year, if a fleet of planes were used as the delivery mechanism. (Dr. Ryo Moriyama, of Japan's Institute of Applied Energy, told me that a study he conducted found the cost was likely double that.)

"The cost of transforming energy systems is in the trillions of dollars of year," Caldeira says.

"My impression has been that if there was a demand to start putting something up in the next couple of years, that it wouldn't be too much to build a fleet of airplanes and just start doing it," he goes on. "It might be that this idea of doing it with balloons or artillery shells or whatever could end up being cheaper, but I think that just even doing it with airplanes is not so expensive that if there was ever a perceived emergency, I think people would just start doing it with airplanes, and then if you can work out something that's cheaper later, maybe do it."


Molly Johnson, Flickr

So what might that perceived emergency look like? How does Caldeira imagine we might be forced to live in a world where the climate itself is consciously being artificially regulated?

"For me, the most likely scenario for deployment is if it just gets too hot to reliably grow crops in the tropics, and tropical countries say, we're going to take matters into our own hands and make our climate so we can grow crops; and say look, you in the north, you wrecked up our climate, and we have a right to try to counteract what you've done."

Scenarios like this are enough to push most climatologists and scientists away from the idea. Many view it as a sort of Pandora's box—the further researchers open it, the more likely it is that a bona fide scheme to meddle with the global thermostat will lurch out.

Partly for this reason, Caldeira has been a controversial figure; he's been profiled in a New Yorker in a piece called 'The Climate Fixers', he was a subject in Jeff Goodell's general audience geoengineering book, How to Cool the Planet, and, perhaps most famously, a source in the sequel to Freakonomics. There, controversy ensued after he was allegedly quoted out of context to help build the case that scientists were worrying about CO2 emissions too much—and that geoengineering was the smart, economical fix for the planet's problems. This despite the fact Caldeira's peers have described geoengineering, scientifically, as "a bad idea."


Still, Caldeira says attitudes are shifting among his fellow climate scientists.

"Our first geoengineering paper was in 2000, and people at that point wanted to distance themselves or not even talk about it," he said. "Then, maybe the late 2000s, people were more vocal about it, but more like saying, 'Oh, bad, bad, bad, we don't want to even think about that.' Now, in the last three or four years it's almost become a trendy research area, at least among some subcomponents of the climate crowd."

In fact, Caldeira fully expects to see a small boom in geoengineering.

"I think it's one of the few areas of climate science that's perceived as a growth area. You know that certain people are coming into it graduate students thinking of it as a career direction," he tells me. "To me, I think it's a little bit dangerous, in that if people are working on a bunch of things, and they spend 10 to 20 percent of their time on geoengineering, they don't have that much of a stake in certain outcomes. But as soon as there are people whose main job is to work on geoengineering, they have an incentive to keep it going… as soon as you start creating institutions to research stuff, what's the main finding? Needs more study, give us more money."

Caldeira seems genuinely and deeply conflicted about the prospect that humans might, someday soon, attempt to tinker with the planet's climate system. When he goes on stage to deliver his talk, he seems anxious, a little overwhelmed. He oscillates between thoughts, jumping from what seem like prepared remarks to notions that just occurred to him then and there, on the fly. He says we should think of geoengineering more like building a dike; there are pros and cons, environmental hazards and benefits. But ultimately, it might buy dwellers on vulnerable ground some crucial time to get their house in order.

Later, when we're talking at length, I ask him how likely it is he thinks humanity might embrace this climatic nuclear option.

"I know people who think it's inevitable that society will eventually deploy one of these schemes just because the potential to offset a lot of climate change impacts very cheaply is there. If people really get hit by heat wave after heat wave and there are droughts and crop failures and people are feeling like 'Oh, the climate models are saying that this would alleviate the problem and it would be cheap,' pressure could build to deploy it. I think that there's at least a 10-20-30 percent chance that we're eventually going to do it."

He shakes his head, and forms a melancholy smile.

"I go back and forth. Most days I think we're never going to do it. Most days, I think we're just going to muddle on and we're not going to reduce emissions and we're not going to geoengineer and the Earth's just going to get hot and the ice caps are going to melt and we're just going to muddle through. That's my view most days."