IAMA Climate Scientist who studies ideas to directly cool the planet to reduce the risks of climate change, known as solar geoengineering, and I think they might actually be used. Ask me anything.

So, what is the most promising technique (cost, acceptance, control) ?

There's been lots of proposals, many of which don't make much sense and only a couple that do. People proposed mirrors in space (very expensive!), desert albedo geoengineering (which I showed would shut down the monsoons), and cirrus cloud thinning (unlikely to actually work).

The leading proposal is stratospheric aerosol geoengineering. It would mimic the cooling effect of volcanic eruptions. They add millions of tons of sulphuric acid to the stratosphere (about 60,000 foot up), producing a global layer of haze that persists for a couple of years. We could do this artificially with high-altitude jets at a cost of a few billion dollars per year and offset all future warming.

The other proposal is marine cloud brightening. Here the idea is to spray up sea-salt from the ocean surface into low-lying clouds and whiten them in the same way that ship tracks do. This is only applicable in some places but is being seriously considered as a way to save the great barrier reef.

The leading proposal is stratospheric aerosol geoengineering. It would mimic the cooling effect of volcanic eruptions. They add millions of tons of sulphuric acid to the stratosphere (about 60,000 foot up), producing a global layer of haze that persists for a couple of years. We could do this artificially with high-altitude jets at a cost of a few billion dollars per year and offset all future warming.

The question I have about this is: have the effects of the dimming and subsequent reduction in light for plants/algae photosynthesis ever been modeled? I feel like there's zero chance this won't have downstream repercussions.

The 1% reduction in sunlight will have some impact, but it's likely small compared to the large fertilization effect of CO2 and the impacts of climate change. There's also some research that suggests the haziness would boost productivity

What if for argument sake it all went wrong? Then what? Just curious btw not trying to argue

Have you seen snowpiercer?

Yes, it's really good. There's no risk of a snowpiercer scenario though. There's no reason to try and freeze the planet and if you did and society collapsed then the cooling effect would only lasts a few years anyway.

Oh man, the conspiracy theorists would had the stratospheric aerosol geoengineering.

Stratospheric aerosol geoengineering, which would spray stuff from aircraft, happens to overlap with the chemtrails conspiracy theory. This has led to some geoengineering researchers getting death threats. :(

I would have presumed that reflective mylar could accomplish what mirrors would at a fraction of the weight, cost, and complexity. Why is a solution like this not on your short list?

"Mirrors in space" is a crude way of putting it. Here's a proposal from 2006that gives a practical, if expensive, way of doing it.

I always wonder about the unintended side effects of something so massive like that. How would you mitigate those types of effects?

Stratospheric aerosol geoengineering is the leading proposal and it has some side-effects. This idea would create a global haze of tiny "aerosol" particles. It's goal is to offset the climate changes from global warming and it looks like it would be pretty good at that, though it may lead to reductions in rainfall in some places. If we copy volcanoes and release sulphuric acid it would have some side-effects:

- To offset 1C of global warming, which is roughly the difference between where we're heading currently (2.5 - 3C) and where we'd like to go (1.5C), would require a reduction in incoming sunlight of about 1%

- However, the tiny particles would scatter light making the sky about 4% hazier. This means solar PV would generate 1% less power and concentrating solar power would generate 5% less.

- It would affect the ozone layer, perhaps delaying the recovery of the ozone hole by a few decades (which is recovering from its minimum in the 90s). Though, as it scatters light it may actually reduce the amount of UV reacing the surface.

- It would add to the acid rain problem, perhaps adding 10 million tons of sulphur on top of the ~100 Million tons we emit today as a by-product of burning fossil fuels.

All of these side effects may be reduced if we use a different type of particle,like calcite, but sulphur is the devil we know and we know from recent volcanic eruptions (Pinatubo 1991) that it's side effects wouldn't be that bad.

Would the reduced sunlight have an effect on photosynthesis? Like would it hurt crop yields and such?

The 1% reduction in sunlight will have some impact, but it's likely small compared to the large fertilization effect of CO2 and the impacts of climate change. There's also some research that suggests the haziness would boost productivity

Wouldn't masking the effects of ghg buildup by reducing their thermal impact potentially enable governments and industries to further delay cutting emissions while issues like ocean acidification continue to worsen?

Your right, solar geoengineering only masks the warming effect of GHGs and does little* to address their build-up. It takes the warming out of global warming, but GHGs and CO2 in particular have direct effects that won't be addressed. These include ocean acidification, plants becoming more productive and water-use efficient (which is not all good!), and impacts on atmospheric circulation including a suppression of rainfall, that would all persist.

You've hit on one of the biggest issues. By reducing the overall threat from climate change it could reduce the incentive to cut emissions quickly. However, I don't think that's a great reason to avoid thinking about an idea that could reduce the risks of climate change. I mean that's the main reason we are cutting emissions in the first place.

(*) - by lowering temperatures it would actually prevent the melting of the permafrost and the degradation of soil carbon which are expected to add considerable amounts of CO2 to the system, on top of what we are emitting.

How do you raise funds to make the change happen? Does it rely on governments or charities or crowd funding or private companies?

This is all still at the idea phase, and it's an idea we'd want to be really sure of before we do anything. So far the research is mostly focused on the consequences and implications and is probably about equal parts spare time / informal, government-funded, and philanthropically funded. Here's a 2018 overview of research funding

Edit - noone has tried crowdfunding, but I'm considering it as a means of supporting outreach activities on this.

What's something that people think makes a difference when in fact, it's kind of a waste of time?

What's something that people could do tomorrow that would make a genuine and meaningful difference that people blow off?

At this point are you comfortable with the science that the benefit of solar far outweighs the cons? How about EVs?

Plastic straws - trivial

Not eating meat - large contribution to personal emissions

Solar power is fantastic and the pros far outweigh the cons, same with EVs: https://www.carbonbrief.org/factcheck-how-electric-vehicles-help-to-tackle-climate-change/

What if we had all the robots vent their exhaust in the same direction at the same time, moving the planet slightly farther from the sun?

Or we drop a giant ice cube in the ocean every few years!

Is there any chance that news of promising geoengineering techniques might encourage the public to do less towards climate change? Obviously the answer is to use it in combination with all the other things being done, but some people will use any excuse they can to avoid change.

Yes, I think this is a real possibility. It hasn't materialized yet, but it's a big worry for many of us in the field. However, I think fossil fuel interests already have plenty of better arguments they can make to delay efforts and I think they know that promoting this would generate an enormously negative reaction.

What do you think of the MIT space bubbles plan?

They don't say how many tons of stuff they'd need to get to orbit. That's where it lives and dies. Getting stuff to orbit is SUPER expensive. If their idea is really mass efficient, then maybe.

Can you please reference a source?

https://senseable.mit.edu/space-bubbles/

If we were wildly successful at reducing albedo by injecting reflective particles into the upper atmosphere - enough to stop or even reverse warming - what would that mean for c02 in the oceans? Would there be additional effects from the build-up of greenhouse gas even without temperature change? Also - could temperature change alone be enough to restore AMOC circulation?

It woudn't have a very big impact on CO2 concentrations. However, it would reduce the melting of permafrost which is expected to release CO2 and methane as it melts. Colder waters are somewhat better at absorbing CO2 so solar geoengineering would increase the fraction of CO2 stored in the ocean. The net effect on ocean acidification would depend on which of those two factors is larger.

The Atlantic Meridional Overturning Circulation, which drives the gulf stream, is slowing down due to climate change. The warming and the freshening (more rainfall) of the North Atlantic reduces the formation of the cold, salty brine that sinks there and drives the circulation. It seems likely that solar geoengineering would reduce that change.

If we raised the albedo of all man made structures (paint roads, parking lots, roofs etc white, or cover them in white sand) - would that move the needle at all?

Globally, not really. However, it could make sense on a city-level. In fact, I think several cities have policies to do this kind of thing.

There's a large "urban heat island effect" that makes London and other cities much warmer than the surrounding countryside. Part of that warming effect is due to the fact that urban spaces are much darker than natural vegetation.

What’s your take on CO2 capture?

It's looking promising, but there are much cheaper things to be getting on with like installing heat pumps and insulation.

There is some debate on whether particulate matter in the upper atmosphere-- from airplane exhaust-- is beneficial or harmful for climate change.

One side says the particulates "seed" high altitude clouds which act as a blanket, trapping heat against the earth at night, when temperatures would normally be cooler.

The other side says the particulates work to deflect heat, as stratospheric geoengineering is hoped to.

What is your position on high-altitude airplane exhaust?

I believe the net effect of contrails is a warming and it's a big part of the total effect of aviation on global warming.

The covid shutdowns provide a natural experiment that this study uses to calculate its impact

Personally, which RCP scenario do you think we're most likely to be on by 2050? Do you think RCP 3.4 is possible with solar geoengineering?

Countries have told us what they'll aim to do by 2030. In the UK, Germany, USA, etc. they will cut emissions rapidly and aim to achieve net zero by around 2050, China aims to get there by 2060, but in the rest of the developing world emissions will keep rising over the next 10 years and likely continue doing so for a while after. The net effect is that emissions will be roughly the same as today in 2030. Beyond that it's hard to say, but I'm pretty confident that emissions in 2050 won't be higher than today, but I doubt they'll be lower than half what they are today.

In technical terms, I think we'll likely be somewhere between a 4.5 and 3.4 scenario.

Following the plot of Neal Stephenson's latest book "Termination Shock", Could a private citizen accomplish this? Legally and financially speaking

No, not really. In fact, I spoke to Neal Stephenson about this and he agreed it's unrealistic, but makes for a good story.

https://www.challengingclimate.org/1873533/9859141-neal-stephenson-on-solar-geoengineering-and-termination-shock

Given all the climate science, you think as a society we should put most of our efforts into prevention or adaption efforts to fight climate change?

We need to do both. Every ton of CO2 adds to warming and so the problem will only stop getting worse once we stop that. However, further climate change is inevitable and we need to adapt to it.

I believe that in rich countries, cutting emissions should be a higher priority, whereas poor countries should focus on themselves first and work to adapt to climate change.

During the proposal phase of these ‘solutions’, is there a discussion or better yet a plan if the solution has unintended consequences?

For example, doping the atmosphere, you listed some expected side effects. If they are stronger than anticipated or have side effects not expected, is there a way to undo the solution?

Based on how little we still understand about the complexity of the global climate system, I have strong skepticism regarding these types of solutions, aside from the ‘get out of jail free’ card that this tech will give carbon emitters

Good question. When it comes to unknown unknowns or unintended consequences, I find it useful to think about which domain will they occur in. For stratospheric aerosol geoengineering, there's basically 2: Fast, chemistry effects in the atmosphere, and slow, climate effects. Changes in chemistry will be detected very quickly as these processes will kick in as the materials are added and should be readily detectable, so if something weird is happening we should pick it up and be able to abandon the effort before much has happened. When it comes to climate, these effects materialize only slowly so we can't really test it before we do it. However, as the impacts of climate change itself are huge, any unintended effects of solar geoengineering would also have to be huge to rival them.

For stratospheric aerosol geoengineering we have the natural experiment of major volcanic eruptions. As these do roughly the same thing that we'd do they give use a great way to test our models and some real-world constraints on what's possible.

Realistically, what are the political/financial barriers for large scale geoengineering

I'd say the biggest barriers are:

- financial / techncial - to do stratospheric aerosol geoengineering you'd need to develop a new, high-flying jet that can reach the tropical stratosphere, build hundreds of them, and fly them from multiple airbases at different latitudes (longitude doesn't matter). Only the big powers have the technical capability, resources and access to do it.

- Youd' need a good justification - whoever would do this would want to be sure it makes sense before they spend tens of billions of dollars developing the kit. That presumably means that you'd want to spend billions of dollars studying it first to be sure.

- geo-political - Any power which tries to change the global climate using these ideas is going to attract a lot of attention from other nations. Any nation, except perhaps the superpowers, would be threatened or sanctioned if they tried this without broad support.

Do we stand a chance?

Texas has water restrictions in place. Everything is crunchy and barren. Water levels in lakes and rivers are plummeting. And the last three record breaking historical highs have happened in the last week.

Does this and can this save us, and what company do I need to send my resume to to make a difference?

I don't believe we are doomed. Climate change is a very serious challenge and in some places it will be the biggest challenge they face this century. While climate change is making many weather related disasters more intense, the world is substantially more robust than it was a century ago. In fact, the number of people dying in disasters has fallen by a factor of 10 over the last century, despite populations tripling or more.

I don't know much about texas but it's much wealthier than most places so I'm sure they'll be able to cope, even if adapting to climate change means abandoning some important things.

How do you deal with the anxiety that comes along with an area of research like yours?

Personally, I'm not anxious. This is likely a combination of my naturally sunny disposition, my familiarity with the issue, and my understanding that the past was a substantially worse place than the present. Climate change is a tragic situation, no doubt, and will make the world shittier, but there are developments that are making the world less shitty that are likely to continue.

Climate risks result from a combination of hazards (e.g., floods) and the exposure and vulnerability of societies and ecosystems to those hazards. The same hurrican hitting Haiti and Miami will have a much more devestating impact on Haiti. As more of the world moves out of absolute poverty into poverty, and from poverty to getting by, etc. we are becoming less vulnerable to climate change.

This is not to say that this isn't a serious problem and it will likely really screw over vulnerable people, particularly the poor in the Tropics, but there are hopeful signs and there is a lot we can do to make the world more resilient.

Back to anxiety, I also believe that if I'm wrong and things do seem to be turning towards the apocalyptic, I'm confident that solar geoengineering would be developed and deployed and that it is likely to greatly reduce those risks.

Does the new L1 bubble shield proposal from MIT actually change the risk profile meaningfully, or is it mostly hype that ignores major issues?

Also: do you have a rough estimate of the cost difference between that and the best stratosphere proposal?

They don't give a cost and they don't say how much mass they need to get into space. Getting stuff into space is super expensive, so I don't think its going to be practical.

Thanks.

Follow-uo: are there any promising options to make the stratosphere idea more reversible? (And do those have cost estimates?)

Any particles that we add to the stratosphere would fall out over the next couple of years, so it's perfectly reversible. One issue that all forms of solar geoengineering face is that if you were offsetting decades of warming and suddenly stopped then you'd get most of that warming back over the next few years. This is referred to as a "Termination Shock" and we'd want to avoid it.

How fast can this hit the ground, scale up, and start making a real sizeable difference?

A manhattan project type effort could get this going in 5 years, but before such an effort is started whoever is launching it would want to know it's a good idea and that'll take years and years of research to figure out. I think it's highly unlikely we'll see it before 2035, 2050 may be more realistic.

Would any proposals help with ocean acidification too?

Not really, though there would be a modest effect from the reduced permafrost melting which otherwise adds CO2 and methane to the system as the plaent warms

Technology enabled ideology to destroy our biosphere. How can we be certain that new technology won't just be subverted again by the underlying ideology and once again used for profit at the expense of the global ecosystem?

Is it wise to continue to develop new technologies without first attempting a revolution in how we think about our relationship with the world? Don't our historical attempts at interfering with ecosystems warn us of the dangers of such a strategy?

Well, it's complicated. Many technologies reduce our impact on the environment. Without the enormous increases in crop yield, we'd have needed an enormous increase in crop area to feed the world: https://ourworldindata.org/crop-yields

I don't think we have the time to wait on a revolution in human values and culture to address climate change. We need to focus on de-carbonizing the economy, adapting to climate change, developing carbon dioxide remocal technologies, and thinking about solar geoengineering. We don't know enough to jump in and deploy solar geoengineering at this stage, but the threat from climate change is serious enough that we shouldn't take options off the table without very good reasons.

Yet without a cultural revolution, we succumb to Jevon's Paradox, where increases in efficiency reduce costs for business owners, which means they expand operations, and overall resource consumption increases.

So long as profits are the central guiding value of our society, I don't see a technological solution. Technology will only continue to serve the interests of wealth consolidation.

I worry about what this push for technological solutions is going to entail for our descendants.

Well, I don't know. We're seeing a decoupling of CO2 emissions from economic growth in several developed nations.

https://ourworldindata.org/co2-gdp-decoupling

Who's going to profit from the geoengineering projects, and who's going to pay the price?

In terms of profit, there's not much to be made. An aircraft manufacturer will be paid to build a couple hundred aircraft, but besides that there's not much. Far less than those companies that will develop machines to capture CO2 will be paid.

It seems like most places will see less climate change, but those who'd like it warmer will be worse off and some places may get drier.

Hi. Thanks for taking the time to do this.

Is there talk of a feasible way to shield Antarctica from the sun? Such as some kind of sun shield satellite?

Antarctica is already very reflective, so the benefits of just reflecting light over it would be muted. however, there are some ideas to intervene to affect the flows of ice into the ocean. These include pumping out some of the water from beneath the glaciers that lubricates the ice flow, and putting up giant plastic screens to keep the relatively warm ocean waters from reaching the underwater ice faces.

You said in another comment that the suggested idea is spraying aerosols into the stratosphere every few years to limit warming.

This kind of sounds like the bit in Futurama of "dropping a huge block of ice into the ocean every now and then, thus solving the problem once and for all!" "But-" "ONCE AND FOR ALL!"

So basically how do we ensure that this doesn't just get used to kick the can down the road for yet another generation to deal with?

We have to keep cutting emissions of CO2. None of these ideas would remove the need to cut emissions and the problem will only get worse until we eliminate CO2 emissions.

What is your opinion on other kinds of geoengineering projects like the ones mentioned below?

I have two Questions One regarding this article.

https://bgr.com/science/mit-scientists-think-theyve-discovered-how-to-fully-reverse-climate-change/

Idea from what I've read is putting some kind of silicon 'cloud' out in space that can block some radiation from the sun. I feel like that's in your wheelhouse, asking pro/con in your opinion.

Part 2 question in regard to stimulating the diatoms in the ocean in order to increase O2 production. (I understand it's slightly outside solar geoengineering) but given your feild I think what you have to say is interesting

https://www.scientificamerican.com/article/fertilizing-ocean-with-iron-sequesters-co2/

Any insight would be helpful. What's a more viable option at this time. Cost effective etc.

Thank you for your time

Anything involving lifting stuff to space is going to be super expensive. It might be a cleaner alternative to stratospheric aerosol geoengineering, but much harder to do.

I don't think we need more O2, capturing carbon would be nice, but any kind of ocean fertilization idea needs to be very carefully considered as it will have large ecosystem impacts.

If we found a way to put the Sulfur Dioxide we already produce into the stratosphere instead of the atmosphere could we prevent future warming without any side effects of creating addition Sulfur Dioxide?

Not directly, but this was the argument that Paul Crutzen (Nobel prize for ozone loss science) made when he suggested people should start taking this idea seriously. our emissions of sulfur dioxide are a big part of our pollution problem, but they have a cooling effect. If we eliminate this pollution, we will face greater global warming. By substituting their cooling effect by deploying stratospheric aerosol geoengineering we can have cleaner air without the extra warming.

Hello. How do you feel about technologies aimed at carbon neutrality for current products, like gasoline from carbon capture?

Also: What scares you most about the technology they may implement vs: not using it?

Well, when it comes to ideas to cut carbon emissions the more the merrier. Generating aviation fuel from carbon capture seems one of the best ways to decarbonize that sector.

How slowly would a project need to be implemented? I imagine quickly deploying whatever geoengineered solution we land on would have shock effects to the environment if the average global temperature were significantly lowered from one year to the next. Would we have to implement our solution slowly, by small percentage points of the full intended effect, over years or decades?

If I were recommending how to do this, I'd suggest several years of very modest deloyment to see what happened, and then scale it up over several more years to start having a cooling effect, before going after your deployment aim, e.g., halting further warming.

If another 30 years were to go by without a change in our current direction, what is the most extreme action we could take for immediate effects? Basically what is our last resort if we're unable to do everything we SHOULD do and want to do?

Stratospheric aerosol geoengineering

So we have abandoned any actual work on mitigation at this point and are fully on the techno-hopium train aren't we?

Nope. no-one in the field sees this as a substitute for cutting emissions.

In the field sure, but the politicians and business interests? They see this as just cart Blanche to not change a thing.

They *might* see it that way, but very few have made that case. I'm also confident that everyone working on climate change would argue vehemently against that view.

What are your thoughts on MEER?

https://www.meerreflection.com/

It seems to be getting hyped quite a lot. I think it might have some potential on the local scale, but it is very unlikely to do much on the global scale as mirrors are just too heavy and expensive.

There have been some post about seeding the oceans with iron or volcanic ash to boost plankton and algea growth in order to sequester carbon with their biomass. The scientist Russ George claimed it would be the solution to all our climate problems but thats pretty dubious and so is the video I referenced below. But I do feel hopeful there is truth to idea.

Other reports have come out saying that there would be an effect but it would not significant enough to shift the needle on temperature rise, due to other factors.Though, there was some mention that it could be one contributor to helping to deal with climate change.

Do you see seeding the ocean with iron or volcanic ash as a part of the overall solution or some fringe belief that need not be considered?

Links below:

Freethink (Youtube) : The highly controversial plan to stopclimate change: Russ George

The Royal Society of Chemistry: Seeding oceans with volcanic ash could be new tool to tackle climate change

MIT News: Seeding oceans with iron may not impact climate change

I think this is only likely to have a small carbon benefit, but would only do so by having a big ecosystem impact. It's a little like irrigating a desert, this would make the desert more useful, but would push out the existing species.

Couple questions:

• OP mentions your focus is on cooling the planet. Do your efforts and ideas account for what could happen if we cool things too much?

• Would you consider (solar) geoengineering to be a relative of terraforming?

The level of cooling would be a choice, so there isn't really a great risk of over-cooling if you scale things up slowly. If it's a little cooler than you thought, you can add a little less to the atmosphere, and vice versa.

Well, I think making Earth more habitable would be a hell of a lot easier than making Mars even remotely habitable.