Antony Funnell: The eruption of Mount Pinatubo in the Philippines in 1991 was an incredible event. So large and powerful was the volcanic outpouring that it actually changed the weather.

News report: Only hours after personnel began their exodus to Subic Bay, the mountain erupted for the first time. Minor eruptions throughout the week set the stage. Wednesday's 40,000-foot mushroom cloud could be seen for miles, and the San Miguel communications complex received what could now be termed a relatively light sprinkling of ash…

Antony Funnell: That mushroom cloud and others over coming days pumped huge amounts of ash into the stratosphere. The sky not only went black over the tropical island of Luzon, but the temperatures on the ground began to fall.

Hello, Antony Funnell here, this is Future Tense.

The eruption also got some scientists thinking about a little known concept called geo-engineering, essentially the use of technology to deliberately manipulate the climate in order to counterbalance the negative effects of global climate change. Their thinking went like this; if we could mimic the way in which Pinatubo cooled the Philippines, by artificially pumping the atmosphere full of sulphates, could we mitigate the warming of the planet caused by greenhouse gases?

Stephen Gardiner: It used to be seen…you know, a couple of decades ago it definitely was seen as extreme and not to be contemplated at all by anyone serious, but now we are seeing major reports from scientific bodies in the United Kingdom and the United States. Germany has a research program and so on. And there are a lot of worries that are expressed by most of the people involved, but a fair number of those people think that given the persistent failure of conventional climate policy reducing emissions and adaptation, that we might be pushed into contemplating geo-engineering some time this century and maybe in 20 to 30 years, as soon as that.

Antony Funnell: Stephen Gardiner, a professor of philosophy and an ethicist at the University of Washington, and he's just finished a visit to Australia where he's been speaking about geo-engineering and some of the many complications around its possible future deployment.

This isn't the first time we've looked at geo-engineering on this program. When we last gave it attention back in 2010 it was increasingly the focus of serious scientific and political debate. It was being talked about by many as the ultimate technology fix for a climate quickly turning sour. But back then, I have to say, it seemed largely theoretical. So what's changed in the last four years?

Clive Hamilton is a professor of public ethics at Charles Sturt University and he's also the author of an authoritative book on geo-engineering called Earthmasters: Playing God with the Climate.

Clive Hamilton: Geo-engineering can be defined as the deliberate large-scale intervention in the climate system designed to counter global warming, or just to offset some of its effects. It covers a range of technological schemes, some are relatively benign, but the more ambitious ones would effectively see humanity mobilising its technological power to seize control of the climate system, the climate system as a whole. Some proposals sound like science fiction, but some of the more serious schemes actually require no great technical feats. Two or three of the leading ones rely on readily available technology and could be deployed within months. And those leading big-scale schemes include ocean iron fertilisation and sulphate aerosol spraying, each of which now has a substantial scientific commercial constituency.

I think the interest in geo-engineering goes well beyond theoretical interest. I mean, there are some scientists of some eminence calling for the deployment of geo-engineering in the form of sulphate aerosol spraying right now. And so certainly the initial surge of enthusiasm for geo-engineering has now plateaued, continued scientific work proceeds. What we are waiting for is for some kind of political break to occur which will open the floodgates for political discussion of geo-engineering.

Antony Funnell: And do you think that's far away?

Clive Hamilton: Well, I was predicting that the fifth report of the IPCC may have been the opening of the floodgates because it for the first time evaluated geo-engineering as a possible policy response to global warming. And there were some forces pushing very hard for a strong endorsement of geo-engineering in that report, particularly Russia. But others were more cautious.

The major nations, in fact all nations, their political leaders are loath to start talking about geo-engineering is a response to climate change because of course they would instantly be accused of shaking their responsibility, sort of abandoning plan A, that is cutting greenhouse gas emissions, for this plan B, geo-engineering. But I think that something will happen sometime soon where a significant political leader will stop talking only in private about geo-engineering, and we know on Capitol Hill in Washington and even in Canberra senior politicians are privately talking about geo-engineering. But once one of them starts talking in public about geo-engineering, then I think that will open the floodgates.

And I know for certain from very reliable sources that state, that is the State Department in Washington, is quite concerned that the climate change negotiations at the Conference of the Parties in Peru this year, or more particularly the crucial Conference of the Parties in Paris next year, 2015, will be derailed by someone throwing the geo-engineering hand grenade into the negotiations, and it is possible that all hell could break loose because it will undoubtedly be an extremely divisive issue. So the State Department in Washington is now developing a strategy to deal with that eventuality should it occur.

Antony Funnell: And research is still continuing, isn't it, research and modelling on the various types of geo-engineering that may well be put into practice at some stage.

Clive Hamilton: Yes indeed, the research continues at ever-gathering pace in the United States, China has now nominated geo-engineering as one of its research priorities in the earth sciences, Russia is quite gung-ho about it. And in Europe there is quite a lot of research going on as well, partly to counter the push of techno-optimists coming from the United States. And there's gathering pressure from scientists and commercial supporters of geo-engineering science to permit and embark on significant experimentation of a range of geo-engineering schemes. So there's a lot happening, not only in the labs, on the computer screens, but out there in the actual world as well.

Antony Funnell: As I'm sure you've realised by now, Clive Hamilton, is no fan of geo-engineering. And the truth is that not many people—even those enthusiastically promoting it—see it as a desirable course of action. They see it as a 'necessary evil', that's the term that's often used.

David Keith is a well-known Canadian environmental scientist. He's a professor of applied physics at the Harvard School of Engineering and Applied Sciences. He concedes it's a contentious issue, but he's one of those who believes it's now time to embrace geo-engineering, that it makes sense, despite the risks.

David Keith: This topic gets steadily more and more attention, attention in both directions; people who think with deep conviction that it shouldn't even be considered and that it so risky or fundamentally against their ethical values that we should touch it, and others who feel it really might be very useful in managing the climate risks. But what you can certainly say definitely is there's much more attention, it's measured by everything from scientific papers to Google hits.

In terms of what's actually new out there for science, I would say if there's one thing it's increasing understanding that it might actually work, albeit with risks. That it might actually on a region-by-region basis be able to really slow down the rate of climate change through most of this century.

Antony Funnell: And you would say, would you, that the serious money at the moment is on solar geo-engineering as opposed to any other form?

David Keith: Yes, the answer I gave was just about solar geo-engineering, these ideas that you could put some very fine reflective layer, say, in the stratosphere that would reflect away a little sunlight and it would partially compensate for the climate change caused by the build-up of greenhouse gases.

Antony Funnell: I know that you've said that you'd like to see the science of geo-engineering move beyond computer modelling to small-scale testing. What progress has been made on that front?

David Keith: No progress in terms of actual tests or even in terms of clear government funding programs that would enable such tests. A fair amount of progress in terms of bottom-up interest by scientists in trying to figure out what such tests could actually accomplish while still having very low risks, and I've been among a handful of people trying to actually figure out what we could do in a relatively low cost, low risk away that would tell us something meaningful about how well geo-engineering might work and what its risks might be.

Is not at all obvious that if you increase the amount of CO 2 in the atmosphere and you attempt to partially, as a band-aid, reduce its climate impact by reducing the sunlight, it's not at all obvious that that should work at all because there are really quite different…what climate scientists call climate forcings. And many of us, including me, actually argued 15 years ago that it really wouldn't work very well, that even if you correct the global temperature you wouldn't correct temperatures on a regional basis or also correct precipitation.

And now a series of studies have shown that while it certainly isn't perfect—this, like any band-aid, isn't perfect—it can really do something to reduce the changes in both precipitation and temperature on a region-by-region basis.

Antony Funnell: Now, let me just stop David Keith there for a second, and let's have a bit of a 'what do we know so far' moment. We know that geo-engineering is increasingly being viewed by governments as plan B in their effort to deal with global warming, even if they're not publicly speaking about it yet.

We also know that politically the issue is coming to a crunch, as Clive Hamilton suggested. On top of that, we understand that while there are many scientists and organisations working on geo-engineering research, actual field testing has been limited, if not negligible to date, at least for solar geo-engineering.

And finally, we know that while there are different forms of geo-engineering, it's really that solar geo-engineering—spraying vast amounts of sulphate aerosol into the atmosphere in order to reflect the heat of the sun—it's really that form of geo-engineering that's increasingly coming to the fore. And one of the reasons why, is cost.

David Keith again:

David Keith: Yes, it's cheap. I think there's a fair amount of consensus that simply doing solar geo-engineering would be very cheap, perhaps 100 or 1,000 times cheaper than cutting emissions, but of course it doesn't do all the things that cutting emissions do in the long run, it can't manage all the risks. And the fact that it's cheap is both good if we decide that we have to use it to partially reduce risks, but also bad because it allows in principle very small states without maybe a lot of forethought to just go ahead and try it. So the cheapness allows unilateral action in a way that could be very dangerous.

Antony Funnell: And it could lead even to wealthy countries deciding, do you think, that they don't need to cut emissions, that this could be a solution that could save them the economic and the political pain of going down an emissions cutting path?

David Keith: That's one of the greatest concerns, and I think the fundamental reason that there was for years a taboo about talking about this was the idea that if we talk openly about the fact that this might partially reduce the risks of climate change, that people will lose their incentive to cut emissions. But I think it is in fact not ethical to say that that is a valid argument against doing geo-engineering because there are in fact quite different decisions humanity faces.

If we want to manage the very long-term climate risks, we must bring emissions down towards zero. But that won't help people in the next, say, half-century very much. If we want to reduce climate risks significantly in the next half-century, solar geo-engineering may do that partially, with its own risks, but the idea that just because there is some risk compensation if we don't do something is really quite unsound.

Like most people, my first reaction was, ick, this seems ugly, it seems exactly against the way my instinct says we should fix the problem. But I believe we should go beyond instinct and look really carefully at what the science tells us and what the trade-offs that we face really are. And in doing that now over two decades I've come to believe not that we should rush to do it, I don't think that in fact, I don't think we are ready to make the decision yet, but that we should take it seriously because there seems like a real possibility that it could substantially reduce risks for ecosystems that I love and for people, especially the most vulnerable people in the world, over the next half-century.

Antony Funnell: Canadian environmental scientist David Keith.

Now, Professor Keith spoke there of a taboo when it comes to talking about geo-engineering, and that's something that geo-engineering opponent Clive Hamilton has also picked up on. In his book Earthmasters he writes about environmentalists in particular deliberately choosing not to debate the topic. And that, he believes, has been to their detriment. So why have they adopted that approach?

Clive Hamilton: Yes, there are a range of reasons. The main one is that we don't want to talk about it because we don't want to give geo-engineering oxygen. Another reason I've divined talking to major US NGOs is that; look, it's not on the table yet, we don't foresee it being on the table anytime soon, our resources are stretched so why would we devote resources to getting on top of it and starting to lobby?

My argument is that everyone, and particularly environmentalists, inevitably will have to come to grips with this issue because it is not going to go away. And therefore rather than be caught flat-footed, NGOs and many other people should become aware of it, understand it, think through the political, scientific and ethical implications, and take a position. And we are seeing in the international debate, whilst the NGOs have stayed away from the issue as if it were an infectious one, we have seen some nations of the south, particularly a grouping coming from South America and Southeast Asia, starting to take it moves in international fora, in particular the convention on biodiversity, to ban or severely restrict research into certain kinds of geo-engineering.

So internationally there are forces starting to position themselves for a debate that will definitely come. And I'm pretty sure that it's not just the US State Department but the foreign affairs departments of pretty much all major countries now monitoring this issue and taking positions, just as the military institutions are in some of the countries of the world…the CIA for example is currently undertaking an evaluation of geo-engineering and its implications.

Mike Hulme: We have reduced the discourse of climate change to this question of global temperature, and that the solar radiation technologies play into that very reduced way of thinking about what the risks and dangers of climate change are. So it fits with this very reductionist notion of what the problem of climate change is. The problem of climate change is not a problem of global temperature. The problem of climate change are the risks and dangers that are presented to people and the things that matter to them, and that happens at local and regional scales.

Antony Funnell: Mike Hulme is a professor of climate and culture at King's College London and the author of Can Science Fix Climate Change? A Case Against Climate Engineering.

He's a proponent of what's called 'the slippery slope' argument. That the nature of Earth's weather systems are so complex that any meaningful field test of geo-engineering would have to be done on a large scale, and once you've done that...well, in for a penny, in for a pound.

Mike Hulme: One of the reasons why this aerosol technology gains attention is that for some people they've argued that all one would be doing, all humans would be doing would be mimicking natural processes, because this is basicly what happens when a major explosive volcano erupts and injects huge amounts of debris, particularly these small sulphur dioxide molecules that coalesce into aerosols, it hides the stratosphere. So one could say that there are natural experiments that had been done whenever a big volcanic explosion goes off, and people often refer back to the 1991 eruption of Mount Pinatubo in the Philippines. So one could look at what happened in 1991 as an analogue and work out, well, this is what would happen if humans deliberately decided to basically recreate a major volcanic eruption.

The other major work that's being done has been nearly all conducted in computer simulation models, so numerous experiments done with different types of models to see what would happen if you did this, if you did that, if you did the other. But those are all reliant on the adequacy of these computer simulation models. We know from many decades of working with these models that they are deficient in many areas, particularly deficient in their simulation of local and regional weather, particularly around precipitation or tropical cyclones.

And anyone who would go ahead with their technology simply on the basis that—well, we know what will happen because we've tested this in our models—I think, again, are living in a crazy delusional world. These models are not reliable enough to act as a test bed for these technologies. We just do not know the full range of ramifications that would follow. And the only way to find that out…in the end…people talk about doing small-scale experiments with the atmosphere, but small-scale experiments are not the technology. The technology only works if it has a global effect. So the only way to test this out is to do it. So for me there is no distinction in the end between a research program and a deployment program. A research program, if it's going to do what a research program claims to be able to do, it has to end up being deployment, and for me that's a very dangerous pathway for a research community to proceed down.

Antony Funnell: If this type of technique was implemented on a large scale, what sort of damage could it cause? What sort of effects could it have on the regional temperature in certain areas of the world?

Mike Hulme: Well, it will have varying effects on surface air temperature, the temperature of the boundary where humans and the things that matter to them inhabit. The more concerning question for me is what happens to regional weather systems that bring wind and rain to people and places. And we know, both from the natural analogues of past volcanic eruptions like Pinatubo, we also know from all of the simulation models that have been attempted, that they show that you can get increased rainfall in many areas, decreased rainfall in other areas. You can in principle have suppression of the major monsoonal circulations of South Asia and of Africa.

Other studies have shown that once you start injecting these aerosols you may well find that you're increasing rainfall in some parts of the tropical world and decreasing it in others. And even if you take those models at face value, let's just say those models are in some sense accurate and precise, if that really is the case, then what is left is a decision to be made by some unspecified agents to decide well, okay, we'll go ahead and do this and we will put the aerosols in in such a way as to increase rainfall for Brazil, but the Africans will suffer because of decreased rainfall, or vice versa, we'll do it in such a way that Africa will get an increase in its rainfall but Brazil will suffer. These are zero-sum games that are just not amenable, I don't think, to the sort of governing principles that any sensible person would want to advocate for the world.

Antony Funnell: So there's no doubt you could have a significant effect. This type of technique could be effective but it would be very difficult to control and to predict what sort of effect it would have on various climate systems, as you say.

Mike Hulme: Absolutely, you would not know in advance, and also the problem then would be if you did implement the technology, let's say after five years there was an evaluation that was made to see what the consequence of this injection of aerosols had been, and let's just say that it had reduced global temperature by a few tenths of a degree, which in the end is ultimately what people seem to think they want to do…so one could even say it's been effective in reducing average global temperature by a few tenths, but how would you then establish whether it has actually been responsible for all of the different variations of weather and rainfall and tropical cyclones that have occurred in that five-year period?

You'd have to have, again, a perfectly accurate and precise attribution system to be able to head off the sort of claims that I suspect would then very rapidly follow from one country to another to say, well, we've had three years of drought following your injection of sulphate aerosols, this is clearly because you've been doing the injection. How would you be able to head off those sorts of claims in international law without a perfect scientific attribution system? And we do not have a perfect scientific attribution system, period. And we are not going to have one for local and regional weather for the imaginable future.

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Antony Funnell: We may not have a perfect scientific attribution system, as Mike Hulme mentioned, but we're also missing any system of international governance that could help regulate how ge-oengineering is eventually applied, if indeed you accept the idea that its application is all but inevitable.

Clive Hamilton again:

Clive Hamilton: At the moment, if we're talking about the big geo-engineering schemes like sulphate aerosol spraying or ocean iron fertilisation, there is no international law effectively covering it. I mean, people have tried to bring it into the convention on biodiversity and the London convention on ocean dumping, but if we are looking at sulphate aerosol spraying there is actually nothing, no legal prohibition on any nation or even a billionaire with a Messiah complex sending up a fleet of planes now to start coating the Earth in a layer of sulphate aerosol. There is a significant anxiety that this could happen.

I mean, look, we ought not to get carried away. If some Dr Evil decided that he or she were going to control the world's weather, even a Dr Good who thought that since the world community can't get its act together I'm going to go and save the world…I mean, you could imagine that if someone like that did attempt to influence the global climate the pressure would be very intense, and if they didn't stop then they'd have their plane shot down probably. But it does emphasise the point that there is a lot of work to be done on international regulatory instruments. And no one is really sure where it should go. My own view is that what needs to happen is that there needs to be a new protocol to the framework convention on climate change governing the research into impossible deployment of geo-engineering schemes. But that's a minority view at the moment. And most nations really don't have a view on it.

Antony Funnell: But even attempting to have any form of regulation can in itself be problematic. For his part, Mike Hulme says he understands the reasoning behind pushing for governance protocols, but he says opponents of geo-engineering who seek to rein-in the concept by developing such protocols also risk validating the legitimacy of geo-engineering through their actions. Once again, the slippery slope argument: formal regulations will quickly lead to field testing which will quickly lead to deployment.

That's also a concern shared by Rose Cairns, a research fellow at the University of Sussex, who's affiliated with the Climate Geoengineering Governance Research Project in the UK.

Rose Cairns: If you are attempting to do engineering at a global scale you are effectively having to create an enormous global infrastructure in order to carry out these projects, and that would be effectively impossible to dismantle later on, even if you wanted to. And it would be associated with all sorts of political commitments, it would be another generation of jobs and all of these kind of things that come along with creating a global industry. So it would have its own momentum and it would it be effectively a form of lock-in that would be very, very difficult to change. And these kinds of lock-ins also raise various issues about democracy, because once you've started this big global climate engineering project, effectively there is no opt-out. So once these things go another step down the line towards deployment, issues of whether or not one thinks it's a good idea become immaterial because it's impossible effectively then to opt out. You are within a globally engineered climate, whether you like it or not.

Antony Funnell: And in that sort of scenario it's very hard then to stop, isn't it, it's very hard to mount an argument to have the funds I guess to campaign against the entity that is created through that initiative.

Rose Cairns: Very, very much so, yes, and I think that that's why it is particularly important for us to take stock at this point and to think about those kinds of issues that often aren't talked about and to say, well, once…if we were to start doing these kinds of things it would be very difficult if not impossible to go backwards. And irreversibility is a very important consideration for governments.

Antony Funnell: Rose Cairns from the University of Sussex, ending our program today.

So is the deployment of geo-engineering technologies inevitable? Certainly a growing number of scientists, academics and politicians think it's increasingly likely. As Clive Hamilton mentioned earlier, the next UN climate change conference is to be held in Peru, and that could provide the next opportunity to see just how much traction the idea has gained amongst international leaders. That conference, by the way, begins on the first of December.

You've been listening to Future Tense. The co-producer for this particular program was Jennifer Leake. The sound engineer Peter McMurray.

Until next week, cheers, and goodbye. I'm Antony Funnell.