credit: carina via flickr/cc license

The Promise and Perils of “Solar Radiation Modification” to Mitigate Climate Change

The Paris Agreement set a target to limit global warming to “well below 2 degrees, but preferably to 1.5 degrees celsius compared to pre-industrial levels.”  However, if present trends continue the world is set to blow past those international targets.

This has lead scientists, the policy community and ethicists to consider strategies on climate change that assume the Paris Agreement targets will not be met in time.  This includes the technological innovation called “Solar Radiation Modification,” which can include the injection of aerosols into the atmosphere to essentially block heat from reaching the earth.

And to that end, my guest today, Janos Pasztor has done some important work on Solar Radiation Modification for global governance and climate justice. He is the executive director of Carnegie Climate Governance Initiative and we kick off discussing what me mean by a global warming overshoot scenario that may necessitate the use of this potentially controversial Solar Radiation Modification Technology.


Apple Podcasts  | Google PodcastsSpotify  | Podcast Addict  |  Stitcher  | Radio Public 



Transcript lightly edited for clarity

What is Temperature Overshoot and Why Does it Matter?

Janos Pasztor [00:02:50] I think in order to understand overshoot, we need to look back a little bit and say that global mean temperature has in fact been fairly constant over the last few thousand years but more recently, as a result of the climate crisis, what we have seen is a substantial increase in global average temperature, and we’re now about 1.2 degrees above historical average. Now this is an average and in different parts of the world at different times, you get sometimes more, sometimes less than the average. For example, at the high latitudes, like in the Arctic region, the average temperature is usually twice as much as the global average so if we’re at 1.2, the Arctic region is more like three. Now there is global consensus through, for example, The Paris Agreement that the global temperature should not rise above 1.5 to two degrees centigrade. And the reason why this level was selected is because scientists feel that beyond that, the world may end up with irreversible impacts. More recently, governments are talking about 1.5 degrees, not the range of 1.5 to two, but simply 1.5.

Mark Leon Goldberg [00:04:09] That’s what they call the High Ambition Coalition coalescing around the 1.5 target, right?

Janos Pasztor [00:04:14] Exactly. Yes, exactly. But there has not yet been a formal intergovernmental agreement to say that now we’re aiming for 1.5. So that’s the situation now why should we be worried about this? Because 1.5 doesn’t look like so much or 1.2, the current level. But the fact is that the current impacts are already pretty bad. When you look around the world, you see forest fires, floods, excessive heat in many places—many impacts are already clearly visible. And what the scientists are telling us is that at 1.5 degrees, it will be much worse. Even that little difference from 1.2 to 1.5., the impacts will be much worse. This is what we saw in a recent report in fact, just at the end of February, the Intergovernmental Panel on Climate Change, the IPCC, in its sixth assessment series, has just published a so-called working group two report which talks about these issues. What this report also says that when we reach 1.5 degrees and maybe beyond it will be increasingly difficult to adapt to those temperatures. And yet we must also recognize that the current trends are actually likely to take us to above 2 degrees centigrade, maybe somewhere between two to three degrees centigrade. And then scientists are saying we can expect catastrophic impacts in many different parts of the world, particularly those who are vulnerable, either vulnerable people or vulnerable ecosystems. So sorry for this long background, but overshoot means that the global average temperature goes above some agreed limit, which in our case is the 1.5-degree goal.

What do global climate trends show? How can governments manage the impending overshoot of 1.5 degrees?

Mark Leon Goldberg [00:06:03] But at current levels, if current trends continue, not only will we overshoot 1.5, but we will more likely than not overshoot 2.5 or even three degrees.

Janos Pasztor [00:06:16] Well, you’re right about that, that the likelihood is going to be more like over 1.5 degrees. So, overshoot is anything above 1.5, including at 1.5, so the point I’m trying to make is that once we’re in an overshoot scenario, i.e., more than 1.5 degrees, the world really has to find ways to start managing the risks of the overshoot in a more structured way than just to simply say that we’ll do some adaptation, and we’ll see how we survive. First and foremost, that means much more radical transformative emission reductions and carbon dioxide removal. But we know that this will take time and the window is closing on us to maintain the temperature at 1.5, as I said earlier, it’s likely that will go higher. So, we have to look at what else the world can do to manage these risks and of course, adaptation is one. But again, the same IPCC report that I just referred to says that there are limits to adaptation because up to a certain temperature level, you can adapt, but then it goes beyond. It’s simply impossible to adapt. So that’s when other issues can come, other options can come and may need to be considered, such as the somewhat controversial solar radiation modification or as some people call it, solar geoengineering.

What is solar radiation modification?

Mark Leon Goldberg [00:07:42] So let’s discuss that because given the likelihood, frankly, that overshoot is a probability, that the international community, that governments around the world will not take the requisite steps necessary to keep temperatures under that 1.5-degree global average and will overshoot it by a substantial degree. These other options may become more and more prominent, more and more relevant in the coming years, and one that you’ve identified is solar geoengineering. Can you explain first, what is that? What do we mean by that?

Janos Pasztor [00:08:21] OK, so solar geoengineering and we use a different term, we try to use the terminology of the Intergovernmental Panel on Climate Change, Solar Radiation Modification.

Mark Leon Goldberg [00:08:31] Solar Radiation Modification. I will banish solar geoengineering from my lexicon forever.

Janos Pasztor [00:08:37] Good!

Mark Leon Goldberg [00:08:38] We shall refer to the former. Go right ahead.

Janos Pasztor [00:08:41] Now solar radiation modification or SRM for short have different techniques, but they all involve the change of the reflectivity or albedo, as scientists say, of the Earth, of the surface of the Earth to reflect some of the incoming sunlight back into space and thereby cooling the planet. So, there are different ways of doing that. There are basically three main families of techniques. The first one is so-called ground-based albedo modification, and that’s the very simple, traditional things like painting roofs white, traditionally that has been used in many places. It keeps places cool locally, but it is not something that one can apply globally. But there are also nature-based solutions there, such as different plants have different kinds of leaves and different reflectivity, so it is possible to select certain trees that may reflect more sunlight back into space and thereby also cool the local areas. But ground based tends to be generally local. Then there is something called marine cloud brightening, which is more of a regional approach and in that technique, one takes seawater and sprays it into the sky near the coastline, and that forms clouds. And when clouds form, that forms a certain shade, and it reflects sunlight back into space and thereby cools the area underneath it. The Australian government is currently experimenting with marine cloud brightening to try to save the Great Barrier Reef, using this method as one of a number of options that they’re looking at.

What is stratospheric aerosol injection? Could it help lower global temperatures?

Mark Leon Goldberg [00:10:26] So just to be clear, the marine cloud brightening, this exists currently? Does the Australian government have pilot projects ongoing or is this like a technology they’re working on developing?

Janos Pasztor [00:10:37] It exists in an experimental, I don’t know if pilot project is the best, but they are experimenting with actual ships, actually spraying stuff into the sky. So, in that sense, it exists, but it’s definitely at an experimental level and it is not being rolled out in any way at this stage. And by the way, that’s true for all the solar radiation modification methods, but I’ll come to that in a moment. The third family of techniques, which is the one that is being the most researched and most talked about is stratospheric aerosol injection. It’s a very complicated phrase, but what it means is that you take materials that you spray into the lower stratosphere from airplanes or balloons, which once up there, they’ll get mixed up and spread out through the whole globe, those particles will reflect sunlight back into space and thereby cool the planet. This one exists only in computer models, not even in experiments yet and scientists feel fairly sure that it would work mainly because they are natural analogs. When a volcano erupts, you get a lot of the same materials that scientists are thinking about putting into the stratosphere. They are also thrown into the atmosphere along with the rocks and the Big Bang and everything else. But it was possible to measure during major volcanic eruptions such as the 1981 Mount Pinatubo eruption in the Philippines, that after the eruption, the global temperature went down by about half a degree for almost two years. So, the scientists are saying we can do this better without the Big Bang and the rocks. We just do it more efficiently so that’s the basic idea of stratospheric aerosol injection.

When could these climate technology solutions be implemented?

Mark Leon Goldberg [00:12:47] On stratospheric aerosol injection: as you say, it’s being modeled with computers. Is there a sense in the scientific community that if they wanted to sprint ahead and do this, how much longer would it take? Are we talking like decades away or are we talking about just a few years away from implementation?

Janos Pasztor [00:13:13] So the scientists who are more heavily involved in this exercise in terms of modeling and so on, would say that if there were to be a coordinated international research program to figure out everything that we don’t know about this technology, this technique, it will take about 15 years before the world could be ready to start thinking about deployment. You know, we are somewhere in between the range that you mentioned.

Mark Leon Goldberg [00:13:46] Yeah, it’s not something that’s part of science fiction. It’s achievable in the not-so-distant future.

Janos Pasztor [00:13:57] It is achievable. And, you know, it’s not science fiction because in fact, currently you can say something like this is happening, not intentionally, but because of human activity. Currently, fossil fuel combustion results in the release of aerosols at the ground level, mostly from power stations and also from cars. And in many countries, that part of their pollution related to the sulfur content of the fuel will have been scrubbed out, so it doesn’t go out into the atmosphere. But in many places, it still comes out as local air pollution and that pollution rises into the atmosphere and cools the planet. It is cooling the planet currently to about half to one degree centigrade. And the point of this is that when the big cities of the world where local air pollution hasn’t yet been cleaned up, but it soon will, once it’s cleaned up, then the temperature will jump by half to one degree. And so, it just means that the work is going to be even harder to deal with the temperature increases that the world is facing.

Why is solar radiation modification not a solution to the climate crisis?

Mark Leon Goldberg [00:15:15] So to the extent that overshoot becomes more and more likely, and as overshoot becomes more and more likely, options like stratospheric aerosol injection become more and more potentially attractive, it carries with it some profound ethical considerations which I know you have spent a lot of time thinking through. Can you walk me through some of the tradeoffs or ethical challenges that accompany solar geoengineering or better put it, solar radiation modification?

Janos Pasztor [00:15:52] Yes, I will try to do that but before going there, just one more important characteristic of solar radiation modification techniques. These techniques are actually not there to solve the climate crisis. The only solution to solving the climate crisis is to reduce emissions and remove carbon from the atmosphere. Those are the only two things that will actually eventually solve the problem. The challenge that we have is that those actions take a long time, and while that is happening, the globe is going to heat up, as we have discussed earlier. And so there comes scientists who say that, ‘well, if you use solar radiation modifications, such as stratospheric aerosol injection, you could keep the temperature rise to a certain agreed level while the world is reducing its emissions and while the world is decarbonizing, removing carbon from the atmosphere,’ so it’s not a solution, it’s more like a Band-Aid that you have to do while the concentration of greenhouse gases is reduced in the atmosphere…

Mark Leon Goldberg [00:17:07] It can theoretically buy you some time before you implement more sustainable solutions.

Janos Pasztor [00:17:11] Yes, but you have to be careful about that approach because when you say buy time, you could end up in the so-called moral hazard that people will say, ‘Oh, if it can buy us time, then we can continue to emit greenhouse gases. We don’t need to bother about emission reduction.’ So, we have to be super careful there because the priority remains emission reductions and carbon removal. Without doing those intensively solar radiation modification makes no sense. And then if you were to apply solar radiation modification without doing the massive emission reductions and carbon removals you commit to having to do that forever and that has its own challenges that come with it. Now you asked for some of the ethical and other challenges that would come or could come with the use of this technique. And there are plenty. In fact, the technology itself is not that complicated. The real hard issues are the governance, the broad governance questions. To start with, who should decide to do this? Now when you talk about stratospheric aerosol injection, even if you inject these gases at one particular location, the impact will become global. It is the most global action one could imagine, so it will affect everybody in every geographical location and unfortunately, not necessarily equally so one of the first ethical questions that arises is how does one deal with those who will end up being worse off? Even if it’s a small percentage, you know, if it’s just 5% of the people will be worse off, 5% of 10 billion people is a lot so how do you how do you deal with unequal impacts of stratospheric aerosol injection?

What are the ethical implications of solar radiation modification?

Mark Leon Goldberg [00:19:08] And what might be a harmful impact of this technology?

Janos Pasztor [00:19:15] So the way this technology would work is that it could reduce temperatures or reduce the growth in temperatures, either way, okay, but the problem is that even if the system works to reduce the temperatures, it cannot bring back the climate to what it used to be. Because the climate will have changed, things will have happened, so you will get all kinds of regional effects that could be quite different than the global average impact. You could get more rainfall or less rainfall in some areas. Now, for some people, that may be useful. You know, if you’re in the Sahel and you get a bit more rainfall, then you say, ‘Well, I’m happy.’ But if that means that in India, there will be less rain, then of course India will not be happy. So, there are these kinds of issues that arise, and any governance framework that one puts in place to make such a technology work will have to take into account these kinds of governance challenges that will arise that will need to be addressed.

How much would solar radiation modification cost? Who would pay for solar radiation modification projects?

Mark Leon Goldberg [00:20:23] Another sort of interesting wrinkle on the governance question is that I take it that this technology is not super expensive. We already have here in the year 2022, private individuals with their own space fleets, who knows what that will be 15 years from now. And it seems that one ethical consideration is like, who gets to do this?

Janos Pasztor [00:20:53] You’re absolutely correct. One challenge of this technique is that it is relatively cheap. The more recent studies seem to indicate that of the order of 10 billion dollars a year, you could actually implement a global stratospheric aerosol injection program. That is a lot of money for you and me, but it’s not a lot of money when it comes to global climate action. When you think about the cost of emission reductions and other mitigation activities, you’re talking about trillions of dollars annually. Now if you were to do solar radiation modification, you wouldn’t do it instead of emission reductions, you would have to do it in addition to emission reductions. But as you said earlier, the fact that it’s just a few billion dollars, there are quite a few individuals who could actually do it themselves. And you know, they may want to save the world, and one billionaire or one or two billionaires could come together and say, we’re going to put all our money to save the world and we’re going to start doing this. The challenge is that they wouldn’t break any rules because there are no governance frameworks that that either prohibit the use of this technique or which would guide the world on how to implement such techniques in some kind of multilaterally agreed fashion. So it would be quite challenging to see how individuals who are wealthy, who would want to do it—and even if it’s not just themselves, but they could get together with a few countries, let’s say a few small island countries who are desperate because  even a 1.5°C temperature rise is going to flood their islands, their countries will disappear, so they’re desperate and you could envisage a scenario where such countries get together with a few wealthy individuals, and then it’s the countries who do it. Then again, it’s a question of international relations, but those countries wouldn’t be breaking any rules. These are the kinds of questions that the world needs to figure out before considering seriously these kinds of techniques. Some people say that this technique is ungovernable. Well, I’m not sure if it’s totally ungovernable, but it surely will be quite difficult to actually work these out. Our track record in the world is not very good at good solutions, which lead to climate justice and other justice in the world. So, these are really serious questions that need to be addressed because if there were to be unilateral actions by countries or individuals, that can result in very substantial global security challenges. And frankly, as we see the world today, we don’t need any more geopolitical security challenges added to what we already have.

How could the UN be involved in the governance issues of solar radiation modification technology?

Mark Leon Goldberg [00:24:17] So, given that that this technology is still many years away, what opportunities do you see exist for appropriate governance of solar radiation modification? Does the United Nations or the United Nations Environmental Program or other multilateral forums provide an opportunity for thinking through the kinds of governance questions that would be required should this technology eventually be deployed?

Janos Pasztor [00:24:51] In theory, a number of UN entities have some kind of limited mandate to address some parts of these issues, and some have also addressed some parts of these issues. We need to start with the Intergovernmental Panel on Climate Change, the IPCC, which has provided information about these techniques in its past and its current reports, and it will probably continue to do so in the future. The UN Environment Program is a place where there were already some discussions about the governance of carbon removal and solar radiation modification three years ago, and there was a resolution that was submitted by some countries at that time, there was no consensus on that, and maybe at some point in the future that will come back. So, there are rules for many of these different entities. UNESCO has done some work has been doing work on the ethical issues related to solar radiation modification. But what is really missing is a kind of an overview of how the world is going to address this issue of temperature overshoot and what the implications are for different UN entities and for, of course, UN member states and for the world as a whole and that is the role that could be played by the UN General Assembly. The UN General Assembly is the place where, of course, all the countries have a seat and a voice but more importantly, the General Assembly can address in a transdisciplinary manner issues that cross boundaries because whether or not one thinks about stratospheric aerosol injection, this is not just about climate, it’s not just about environment, it’s also about health, it’s about geopolitical security issues and so on and so forth. So, one needs to have a broad look and the UN General Assembly could frame this issue and provide some overarching guidance to the world on how to address it, how to learn about this technique, how to understand it better and give guidance to the different entities in the UN system and, yes, other inter-governmental bodies, too, to address the issue from the perspective of their mandates and their interest. And then we have a situation where we can start moving forward and we will understand and learn better about this technique. Eventually the world can get ready for some decision making that will need to take place. Not today. The decision making doesn’t need to take place today. Today what one needs to do is learn and understand and encourage conversations. But the time will come in a few years from now maybe, it’s not clear, depends how well we’re doing on emission reductions also, but the time might come when there will be pressure for decision making and the world needs to get there. It will require quite a bit of learning, understanding and that can be achieved through conversations, putting these issues on the agendas and so on and so forth.

Mark Leon Goldberg [00:28:12] Well, you know, I hope for it. We’re advancing the conversation a little bit today through this episode. Thank you. Thank you so much for your time. Super interesting.

Janos Pasztor [00:28:21] You’re welcome.

Mark Leon Goldberg [00:28:25] All right, thank you all for listening. Thank you to, Janos Pazstor, that was really interesting, and I think a really important insight into policy debates and ethical debates, frankly, that will become very much the fore of conversations in climate policy circles in years to come. Thank you. All right. We’ll see you next time. Bye!