Dr. Douglas MacMartin is a senior research fellow at the Sibley School of Mechanical and Aerospace Engineering at Cornell University, renowned for his leading work in climate engineering, also known as solar geoengineering or climate intervention. His insightful contributions have sought to advance the knowledge base needed to support potential societal decisions in this often challenging and controversial matter. His work comprises research and public academic presentations, UN Environment Program briefings, and Congressional testimonies.
Most recently, he was part of the US National Academies panel, which delivered its recommendations on research and governance in March 2021. He holds a PhD in aeronautics and astronautics from MIT.
There are two primary areas of geoengineering, also called climate engineering or climate intervention. The first is called greenhouse gas removal or carbon geoengineering. “Essentially, they have ideas to suck carbon dioxide out of the atmosphere. That concept is not by itself controversial,” says Dr. MacMartin. Projects under this kind of geoengineering can include mass tree plantings, ocean alkalinity enhancement with ground-up materials, and building large machines to clean the air.
The other kind of geoengineering is more controversial, called solar radiation management or solar geoengineering. The primary project under this side of geoengineering is stratospheric aerosol injection. “We are researching putting aerosols in the stratosphere that would persist for a year to reflect sunlight and help cool the planet. Which, in theory, is relatively easy,” says Dr. MacMartin. “But where do you put them? When I started this research, people made models of just putting aerosols at the equator. We started asking what happens when you put them in at different latitudes and treat it as a design problem instead.”
Thanks to Mother Nature, there are recent, measurable, natural examples of particles in the atmosphere cooling the planet. “Nature does this every now and then, so aerosolized particles are not completely unnatural. When Mount Pinatubo in the Philippines erupted in 1991, it cooled the planet by something little less than a half degree Celsius. So we know it works, and we know things that are not good about it,” says Dr. MacMartin.
Starting a career in geoengineering isn’t as straightforward as more common engineering fields such as civil or mechanical engineering. Aspiring professionals who want to work in this field must be creative and flexible in their approach. “Because this field is so small, it can be difficult to jump into it immediately,” shares Dr. MacMartin.
“One advantage is that there's lots of stuff that hasn't been done yet and many unanswered questions on the science side. However, there's a disadvantage because it's interdisciplinary. No matter what, it’s important to have a handle on climate science and how to look at the output from climate models.”
Because this field is interdisciplinary, it is possible to earn an undergraduate and even graduate degree in several areas and then move on to research and work in geoengineering. The options and opportunities are wide open in this emerging field. “The work our group does involves design, optimization, and feedback control. What originally got me into the field was understanding how different people around the planet might think about uncertainty, risk, and how to deal with climate justice issues,” remembers MacMartin. “It's not hard to find unanswered questions because it's such a small field. For example, if you thought, Well, what would the effect of doing marine cloud brightening on ocean ecosystems be? There's basically no research, and you would have so much to study.”
The nature of the research requires professionals in this field to have a keen understanding of policy and potential applications. “If I want to make sure that the research I'm doing is useful, I need to answer the questions that matter. The whole point of doing the research is to be informing policy. So it's critical, both so that the research gets out there and so that you're helping the people who are more involved in policy-making, that you're talking to the right stakeholders,” says Dr. MacMartin. “The opposite is also true. If somebody wants to make contributions on the policy side, it's meaningless if they don't understand enough about climate science.”
Geoengineering is a controversial topic because it involves manipulating the environment to reduce or reverse global warming. It raises many questions, most of which don’t have answers, such as serious ethical and safety concerns. “But climate change isn't good either,” reminds Dr. MacMartin. “So the question then becomes, is it better to perform these interventions in terms of physical climate risk? And then how does it affect people's choices?
He continues, “People are concerned with geoengineering because they worry it is a moral hazard and that we are proposing these interventions as an excuse not to cut emissions. This is something you would do in addition to cutting emissions. Honestly, we are at a point where cutting emissions might not be enough, and we need backups. Cutting emissions alone will still leave us with a radically different climate.”
Another concern to consider in geoengineering is how you go about implementing a project of the scale, such as Dr. MacMartin is researching: “One big question is that of governance. Deploying aerosolized particles would affect every single person on the entire planet. So, who makes decisions about this, and how do you make decisions in an equitable way?” asks Dr. MacMartin.
While some projects can be implemented on the carbon geoengineering side, most solar geoengineering projects are still in the research phase: “Stratospheric aerosols are all still just computer modeling. We have a fair amount of data to anchor our models from volcanic eruptions. There are useful small-scale things to do, but they're microscopic, such as measuring a chemical reaction rate in the stratosphere,” shares Drr. MacMartin.
“There's no experiment to see what the climate effects would be because to do that, you would have to put so much material into the air that you would actually be cooling the planet. And everybody would call that, appropriately, deployment.”
“The other idea with the most traction would be marine cloud brightening,” he adds, “If you spray salt into the air, you can get tiny crystals of salt into the right type of clouds over the ocean. That makes those clouds brighter, so they reflect more sunlight. This method is less well understood, and it would need some very controlled experiments over the ocean to understand changes in cloud properties.”
Due to the progress of our warming climate, some of the research MacMartin is currently working on will likely be utilized in the future. “I'm a bit of a pessimist, and when I look at all of the talk about cutting emissions and how little progress has been made, It is clear that it is really going to be very hard to get our emissions to zero everywhere on the planet,” he says.
“I'm sufficiently scared about climate change that I think it's pretty likely that somewhere down the road, somebody will deploy something like the aerosolized particles. I don't think that's likely in the next ten years, but in the next 20, it's much more likely. It's easy to imagine a scenario where, for example, a heatwave in India kills vast numbers of people, and India says, ‘We're just gonna solve it’ with a project like this. There are so many trigger points that it is almost a question of when rather than if.”
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