E8: TIL about geoengineering


When talking about climate change solutions, we often hear about reducing emissions and adapting to climate impacts, but a third option is starting to get more attention: altering the atmosphere. In this episode of TILclimate (Today I Learned: Climate), MIT alumnus Janos Pasztor joins host Laur Hesse Fisher to explain geoengineering: what it is and the different technologies that are being researched. They also dive into the opportunities and challenges presented by geoengineering, and what difficult decisions we might need to make as a society.

Janos Pasztor, an MIT alum, is the Executive Director of the Carnegie Climate Geoengineering Governance Initiative (C2G2), which seeks to create effective governance for geoengineering; it aims to expand the conversation from the scientific and research community to global policy-making, and to encourage a society-wide discussion about the risks, potential benefits, ethical and governance challenges. Before his current position, Mr. Pasztor was the UN Assistant Secretary General for Climate Change and the Policy and Science Director of the WWF (2012-2015). From 1993–2006, he worked at the secretariat of the UN Framework Convention on Climate Change.

For more short climate change explainers, check out: www.tilclimate.mit.edu.



Special thanks to Tom Kiley and MIT Open Learning.
Produced by the MIT Environmental Solutions Initiative at the Massachusetts Institute of Technology.

JP: [00:00:00] Who should decide whether or not we should even consider this technology? Should it be one country unilaterally deciding? Or should a group in the UN General Assembly sit down and decide, or in the board meeting of Exxon Mobil?

LHF: [00:00:21] Welcome to TIL Climate, the show where you learn about climate change from real scientists. I’m your host Laur Hesse Fisher, from the MIT Environmental Solutions Initiative.

When people talk about climate change solutions, they’re usually talking about either stopping adding CO2 to the atmosphere, or how humans can adapt to climate change. There’s also a third option that’s starting to get more attention.

JP: [00:00:47] My name is Janos Pasztor. I am Executive Director of the Carnegie Climate Geoengineering Governance Initiative.

LHF: [00:00:55] Mr. Pasztor is an MIT alum who was appointed by Ban Ki-moon, the United Nations Secretary-General, to lead his office on climate change. He also worked on the UN Paris Agreement, where nearly every country around the world pledged to cap global warming.

JP: [00:01:10] Climate change action has been focused first on reducing emissions, which was correct. Then at some point people started thinking that we also have to adapt to the changes that are already taking place. But now when we put everything together, we have to realize that there is something else that is needed.

Even if one were to stop all global emissions today, which of course is a very difficult thing to do, but even if we were to do that, there's enough carbon in the atmosphere that global temperatures would still rise and would stay like that for a few hundred years. So we have a problem.

LHF: [00:01:51] In addition to no longer adding CO2, we also need to take CO2 out of the atmosphere. And if we can’t take out the CO2 fast enough, then we could try to reflect sunlight or otherwise stop the earth from warming.

This is why some people are starting to talk about geoengineering.

JP: [00:02:12] The way it's defined it is "intentional large-scale interaction with the atmosphere." Large scale meaning planetary scale, in order to address the climate change problem.

LHF: [00:02:26] Generally speaking, there are two types of geoengineering: the first is about sucking existing carbon dioxide out of the atmosphere.

There are lots of way to do that. We all know that plants absorb CO2, but so do soil and rocks, and there are things we could do to help accelerate what nature already does. People are also creating chemicals that react with the CO2 in the air, capture it, and turn it into something that could be stored or used for another purpose, like plastics. We could also combine these two approaches: grow plants, burn them for electricity, but then immediately capture the CO2 and store it, which could produce energy and suck CO2 out of the atmosphere. If you want to learn more about these technologies, we’ll have some quick reads in our show notes.

While there are definitely things that need to be worked out -- like land use issues and how to pay for these technologies -- removing carbon dioxide out of the atmosphere is something people are paying more attention to.

JP: [00:03:26] There are lots of experiments going on lots of little companies doing things. We saw that at the UN climate change conference in December of 2018, there was a lot more discussion about carbon dioxide removal than ever before.

LHF: [00:03:41] But where there’s less known -- and more debate -- is with the second type of geoengineering, called solar radiation modification.

This kind of geoengineering doesn’t try to reduce the CO2 in the atmosphere -- it focuses on reducing the amount of heat that gets trapped there.

JP: [00:04:01] There are ways to change the clouds and make them thinner or make them more reflective to alter the radiation balance of the earth. But there are other methods like changing the albedo of ice for example in the Arctic. There's an experiment going on right now in Alaska to do that. Both of these would result in cooling the planet.

Now. This looks like science fiction stuff, but one thing that people have thought about is space-based mirrors. You know shoot up a bunch of rockets and put up big mirrors that would literally reflect sunlight back into space before entering the atmosphere.

So there are different things scientists think we can do, but the one that is most commonly talked about is the stratospheric aerosol injection.

LHF: [00:04:51] That’s a fancy phrase for spraying a particular kind of particle -- a sulfur aerosol -- into the atmosphere. This part relates back to the conversation we had with Prof. Dan Cziczo in our episode on clouds. I recommend you checking out for more info on how particles help form clouds.

OK, so this technology, “stratospheric aerosol injection”, mimics something that volcanoes do naturally.

JP: [00:05:18] The volcano erupts and lots of gases and rocks and dust and everything else escape, including so called sulfur aerosols that reflect sunlight back into space and cool the temperature of the Earth. And in fact after a major volcanic eruption like the recent one in Mount Pinatubo in the Philippines, the world could measure that actually the global temperature went down by about a half a degree and stayed like that for a year almost and then went up again.

LHF: [00:05:49] And so some scientists are exploring how to replicate this artificially. For example, jets could circle the Earth a few times a day, spraying these particles into the upper atmosphere. And then these particles would reflect about 1% of the incoming light from the sun, thereby cooling our planet.

But of course, there’s no free lunch.

JP: [00:06:12] This technology also has impacts. First of all, it reduces sunlight that comes into to reach the Earth and that will have an impact on agriculture, on forests, on ecosystems. It will also change the weather patterns and we don't quite know how much but we need to find out before we take any decisions.

LHF: [00:06:31] The other issue is if this technology were to be used alone without reducing CO2 in the atmosphere, it’s kind of a Band-Aid solution.

JP: [00:06:39] Once we get going with solar radiation modification, you can't just simply switch it off. If you do it for let's say 10 years or 20 years and you suddenly stop, and you haven’t reduced the concentration of greenhouse gases, the temperature will jump up to what it would have been otherwise. And jumping up quickly would be even worse for the ecosystems then slowly ramping it up. So you're taking lots of decisions for future generations. And once you start it, they don't really have a choice.

And then there of course, and it's the biggest challenge of all, is that we only have one atmosphere. And this technology would manipulate that one atmosphere. If we get it wrong, we've had it. So so we need to be absolutely sure that we're doing things right. There are no easy answers here.

LHF: [00:07:35] In his organization, Mr. Pasztor is trying to open up a global conversation about how we, as a society, make decisions about geoengineering, while these technologies are still young.

JP: [00:07:48] On solar radiation modification, nothing is happening other than a few modeling ideas and a few, maybe some small experiments, but first of all, who should decide whether or not we should even consider this technology? Should it be one country unilaterally deciding? Or should a group in the UN General Assembly sit down and decide, or the UN Security Council? Or in the board meeting of Exxon Mobil?

There is for example, an interesting scientific paper that showed that it would be possible to do hemispheric, only Northern Hemisphere deployment of solar radiation modification, that could help in reducing frequency and intensity of hurricanes in the Caribbean.

There's only one problem: it would result in a massive drought in the Sahel in Africa. You cannot have just the northern hemispheric countries decide, "we're going to do this and who cares about the Sahel?" The systems are interconnected.

LHF: [00:08:46] Interestingly enough, one of the complicating factors of stratospheric aerosol injection is that it could be the cheapest technology to deal with global warming.

JP: [00:08:57] As little as two to three billion dollars annually for the first 15 years. Now that's nothing compared to the global cost of emission reductions or carbon dioxide removal, which should be measured in the trillions.

So these are questions that need to be addressed now, before somebody, it could be that a country decides to announce deployment in a few years from now. Or an individual who is a wealthy person says, "I want to save the world. And I'm going to use my money and I'm just going to start flying these airplanes and start spraying the stratosphere with with the with aerosols."

Geoengineering is not just philosophical, it's not just ethical, but it's actually basically a risk management issue. Each technology has some positive and some negative impacts. There is no Silver Bullet, and there are no easy and quick solutions.

LHF: [00:09:58] So there’s a lot more that we need to know in order to understand how these technologies will work and, more importantly, how parts of the world could be impacted. But once we know, it’s then not a matter of research, it’s a societal decision we’ll need to make about intentionally modifying our atmosphere, our planet.

This episode was one of the hardest one to create so far -- it is a real challenge to boil down something so technologically and morally complex as geoengineering into 10 minutes.

So in our show notes, we’ve included more resources where you can learn more about these technologies and some of the issues that come along with them.

Now you may or may not be a part of the UN General Assembly, but you do have political officials who represent you, and perhaps also may be connected to nonprofit organizations working on these kinds of issues. Share this episode or the resources in our notes with them, and open up the conversation so we can make informed decisions about our future.

Thank you for joining us on this first set of episodes from Today I Learned: Climate. In this past month and a half we’ve learned about how planes and condensation trails warm our planet, how clouds cool our planet and what particulate matter has to do with that. We talked about steel and cement, hurricanes, how to think about risk and uncertainty, how climate change will impact different parts of the world in different ways, and we started digging into the solution areas like carbon pricing and geoengineering. But we are just getting started. This was our first set of episodes and we really hope that you enjoyed them. We’re going to take these next few months to work on another set of episodes for you that we’ll release this September and October, and in the meantime we love hearing from our listeners, so send us your questions, your comments, what you would like us to cover in the next set of episodes. Tweet us @TILclimate or email us at TILclimate@mit.edu. Thank you so much for tuning in, and thank you to Mr. Pasztor for speaking with us for this episode. See you next time.

An educator guide for this episode can be found below.

To learn more, check out:
Mr. Pasztor’s work:

For more information on geoengineering:

More on absorbing carbon dioxide from the atmosphere (carbon dioxide removal):

More on solar radiation management:

An overview of climate change:


Educator Guide

Created by Olivia Burek, Alyssa Farkas, and Aaron Krol, with thanks to Sarah Hansen and MIT Open Learning


The following questions can be used to encourage your students to reflect on, extend, and apply what they’ve learned from the podcast episode. Re-use and remix them as writing prompts, discussion guides, or ideas for project-based learning in your classroom.


Critical Thinking

  • Consider Mr. Pazstor’s question: “Who should decide whether or not we should even consider this technology?” In the past, who has made this type of  decision about issues that may affect huge numbers of stakeholders across the entire planet? (You might consider, for example, the new national boundaries created at the Paris Peace Conference after World War I.) Who should be involved in the decision-making process regarding geoengineering? How can the process be made fair, so that all regions and stakeholders are given an appropriate voice? How might power dynamics between different countries or interest groups play a role in the process? What factors should be considered when debating the implementation of this technology? 
  • Think about how the two types of geoengineering that Mr. Pazstor discussed, carbon dioxide removal and solar radiation modification, differ. Ethically, how do the two methods compare? Does either method generate more of an ethical dilemma than the other? If so, why? What kinds of side effects might each of the two strategies produce? How should these be factored into decisions about the use of geoengineering in general, and about the use of one type over the other? 
  • Mr. Pazstor mentions that stratospheric aerosol injection may be one of the cheapest technologies to deal with climate change. What are some possible short-term consequences of this? And long-term consequences? What are the most important factors to consider when weighing geoengineering against other strategies to prevent climate change or to adapt to a changed planet?


  • Research how the idea of geoengineering came about. Who has typically advocated for it? Who has typically been hostile to the idea? Has weather or climate control ever been implemented before? How, and on what scale? 
  • Research entrepreneur Russ George, who decided to create and undertake his own geoengineering experiment. What exactly did he do, and why? What kinds of environmental effects came about from his experiment? And social effects? What ethical questions does his experiment raise? What is your opinion on geoengineering by individuals or small groups of people?


  • What did you know about geoengineering prior to listening to this podcast? After listening, how effective do you think it could be? Is it worth a try, or is it too risky? 
  • Why do you think climate activists have not been more focused on geoengineering as a possible climate policy? How does geoengineering work alongside, or conflict with, other types of climate action? Do you think geoengineering will become a more or less prominent issue in the future? Why?


  • Debate: in favor of geoengineering vs. opposed to geoengineering


Need additional open educational resources related to the topic of geoengineering? You may find these free teaching materials from MIT OpenCourseWare (ocw.mit.edu) helpful:

Seminar in Environmental Science
Level: Undergraduate
This course, taught by Professor Daniel Rothman, is an introduction to research in the field of environmental science with a specific focus on geoengineering, stressing the integration of central scientific concepts in environmental policymaking. Educators have access to the syllabus, reading list, assignments, and a selection of final papers written by students.
Ecology I: The Earth System
Level: Undergraduate
This course, taught by Professors Edward DeLong and Penny Chisholm, covers fundamentals of ecology, considering Earth as an integrated dynamic system. Educators have access to the syllabus, reading list, lecture notes, assignments, and five student-written research proposals describing pilot projects for assessing various Earth-system-scale geoengineering technologies.
Solving Complex Problems
Level: Undergraduate
This course, taught by Professor Samuel Bowring, revolves around a central challenge: solving the large and complex problems necessary to sequester enough carbon to stop the steady increase of atmospheric CO2 and to stabilize it. Educators have access to the syllabus, reading list, and course assignments.