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In this episode, Dr. Ye Tao discusses his vision for combatting climate change by using fields of mirrors that reflect solar radiation.

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David Roberts

Geoengineering — using large-scale engineering projects to directly cool the Earth’s atmosphere — is an intensely controversial topic in climate circles. On one hand, such schemes strike many people as dangerous hubris, interfering with large-scale systems we don’t fully understand, risking catastrophic unintended consequences. On the other hand, there is good reason to believe that even a wildly successful program of decarbonization will not be enough to avoid devastating levels of heat in the atmosphere.

Dr. Ye Tao was early in his career as a researcher at Harvard’s Rowland Institute, working on nanotechnology, when he became gripped by the problem of climate change. As he dug into the research, he concluded that even rapid decarbonization — especially insofar as it reduces the aerosol pollution that temporarily cools the atmosphere — would leave the Earth roasting in levels of heat hostile to most life forms.

As he reviewed available options for carbon capture and geoengineering, he realized that none of them were safe or scalable enough to do the necessary cooling work in time. So he came up with a technique of his own: mirrors.

The MEER project — Mirrors for Earth’s Energy Rebalancing — is a nonprofit established to advance Tao’s vision, which involves covering some mix of land and ocean with fields of mirrors. The mirrors would reflect solar radiation, and thus heat, back up out of the atmosphere. If 10 to 15 percent of developed agricultural land could be covered with mirrors, Tao has calculated, it would return Earth’s heat to safe preindustrial levels, providing a range of local benefits to agriculture and water in the meantime.

It’s a brash idea, somewhere between crazy and obvious, and I was excited to hear more from Tao about why he thinks it’s necessary, how it would work, the materials that would be required, and how the MEER framework changes the way we view carbon dioxide in the atmosphere.

Alright. Ye Tao. Welcome to Volts. Thanks for coming on.

Ye Tao

Yeah, thanks for inviting.

David Roberts

Ye I have to confess when I first invited you on the pod, I had not yet really done a deep dive into into the MEER Project, and I was just sort of thinking, "Oh, a bunch of mirrors. How novel. That sounds fun. Let's talk about that." But I've spent a while now digging in and listening to more of your presentations and reading more, and there's really a lot going on here. There's a lot going on here. The mirrors are at the end of a sort of chain of reasoning that in many, many ways contradicts conventional wisdom about climate change.

So I do want to get to the mirrors. I'm excited to talk about the mirrors, but let's do a little background building first. So I want to start with, it seems like the key to understanding your whole framework here is the distinction between CO2 and heat. We sort of conflate carbon and heat. When we talk about climate change, what's the problem? It's more carbon, and carbon causes heat. How do we reduce heat? We reduce the carbon dioxide emissions. We sort of have those coupled in our mind. And you say it's important to decouple them. So talk a little bit about why we need to keep them conceptually distinct, and then also decouple them in terms of the physics of the system.

Ye Tao

Okay, yeah, that's a good place to start. It's true that we created this problem by emitting CO2, and it's important to shut it down as quickly as we can manage, practically. And in the Earth system, everything is basically linked. So it's only natural that when you perturb one important component to a very significant extent, such as CO2 concentrations, you should expect some downstream consequences — and the most urgent of which is overheating of the planet. And heat is really the driver of weather patterns and precipitation patterns. So when you have excess thermal energy that's really different from the state Earth was before the CO2 perturbation, that you can expect downstream extreme events and also perturbation to the biochemical cycle.

And if we look at the responses of different organisms and plants, insects, and mammals, and how they respond to individual perturbations in CO2 versus temperature, universally they really suffer when temperature gets ramped up to a few degrees above their normal temperature niche values. But in terms of CO2, essentially most species, like 90% plus or more, are actually not perturbed really by the current increase in CO2 levels. So basically, we initiate this avalanche by burning CO2. But the real environmental stressor that's really creating havoc are a combination of overheating and the resulting drying of land and moisture.

David Roberts

So what we talk about as the effects of climate change are the effects of heat, basically, our heat playing its way through the system. And is it safe to say then that we care about CO2 in the atmosphere more or less only as it relates to heat? Only insofar as it brings more heat, right. Because in and of itself, as you say, it's not, I mean, I'm sure there's some level of concentration that's dangerous, but the levels of concentration we're talking about are not dangerous in and of themselves. Is that fair?

Ye Tao

Well, we'd have to be a little bit more careful and include a timeline. I would say, like in the near future, next 50 years, assuming that we're emitting and growing economy on current trajectory, then the predominant parameter is heat. That's going to basically shut everything down before we're able to continue. But if we were, somehow, we're able to manage to prolong this fossil fuel economy then by the 2070s, 2080s, ocean acidification would then also become a potentially dangerous environmental stressor for marine ecosystems. But the logic is that it's very highly unlikely for society, or civilization, to really survive to that point on our current emission trajectory.

Therefore, we really need to focus on both decarbonizing safely and also dealing with heat. So I mentioned that we initially started this heating process by turning up CO2. And that there are many parameters in Earth system are interlinked. But it's logically just not correct to say that the best way is to use this single CO2 knob to address the heat or moisture. There are other knobs that are higher leverage, essentially, for the same input in resources, energy, and time. And we're stressed on all those fronts. There's much better ways to address the most imminent danger of environmental overheating than looking at conventional CO2 or methane mitigation.

David Roberts

Right. So CO2 is the knob that turned heat up, but it's not necessarily the ...

Ye Tao

Only knob that we have.

David Roberts

Or most efficient knob for turning it down. And you go beyond that to say, that even if we switched to 100% renewable energy tomorrow, you think we would still pass heat thresholds, that would be devastating. Explain that a little bit.

Ye Tao

So currently Earth is on a heating trajectory, and when something is heating, that's because there's more thermal power or more heat that's been put into the system than is coming out. So let's say somehow we could selectively just shut down emission of greenhouse gases, while somehow maintaining economy going, the Earth will continue to heat. The reason is if you make a measurement of how much sunlight is coming in, and how much IR radiation is going out, currently, there is a 1.5 watts per meter squared of power net energy input into the Earth system. So essentially the past emission debt, even in the current state has not been fully paid.

So the Earth will continue to heat up, even if we were to shut down. And I need to explain a little bit what this 1.5 watts per meter squared means. So "watts" is a unit of power, basically how much energy gets passed through per unit of time. And "per meter squared" is an average value that scientists, climate scientists like to use to get some common metric. So basically, you have LED at every square meter of land surface on Earth, that's currently how much heat is coming in continuously.

So to translate this power into an eventual equilibrium temperature, we have to multiply by a factor that converts this weird unit to a degree unit. And that factor has a value that's roughly one. So it's very convenient. So for every watt per meter squared of radiative forcing or this heating power per square area, we can expect at equilibrium a temperature increase of about one degrees. So therefore, we should expect another 1.5 degrees of temperature increase at equilibrium, if we were to just shut down further damage at this point. So that's point number one.

But this 1.5 degrees will not realize instantaneously. It's going to take some time, years, decades, to centuries to realize. And there's different components, different part of this 1.5 will manifest itself over different length scales, but overall, we're looking at order one-degree increase.

So that's assuming that we could somehow selectively shut down CO2 emissions. But when we burn fossil fuel, there are other pollutants that are co-emitted, which includes these aerosols.

David Roberts

I love this. I've been waiting for someone to say something. I've had this question idly in my mind for a long time, and I was so glad that you answered it in your presentation. And it's such a fascinating irony, I guess you'd call it, or paradox or something, and I'm glad to have it measured. So I just want to put a pin in this. So you say if we're burning coal, we're sort of steadily burning coal. And part of what that is doing is putting aerosol pollution in the air, which is blocking some of that solar radiation.

So to some extent offsetting the heating of the atmosphere. And if we stopped burning coal, those aerosols fall out of the air quickly. Unlike CO2, they quickly fall out. So whatever heating they were blocking would very rapidly make its way in. So I guess what I want to ask is, would that more than offset whatever reduction in heat you get from the reduction of CO2?

Ye Tao

That's an excellent question, and let's go into a little bit of semi-quantitative detail. So I previously mentioned that even overlooking this temporary cooling effect, the Earth is currently experiencing a heating power density of 1.5 watt per meter squared. So this quantity is called the Earth's energy imbalance, basically how much surplus heat we're getting right now. And this value has been fluctuating around 0.7 to maybe 1 watt per meter squared in most of the past 10, 20 years. Except for more recently. In the recent few years, it really went up to maybe 1.3, 1.5, even like last year, based on the most recent measurements.

So I won't speculate on why recently there has been an increase in this heating power. Okay, let's leave that Earth energy imbalance aside for a moment and address how much additional heating is currently masked by these aerosols. So the latest IPCC, if you really delved into the technical parts, they put the number at about 1.2, 1.3 watts per meter squared. So it's an important number to remember, 1.2 to 1.3. So essentially, let's now assume that in addition to shutting down the CO2, we also shut down all the aerosol emissions, which comes naturally anyways. We would then induce a Earth's energy imbalance, which is no longer 1 or 1.5, but that number plus 1.2 or 1.3, which brings the total energy imbalance to most likely around 2 watts per meter squared, or somewhere slightly above that.

And if we then translate this heating power to an equilibrium temperature increase, it will be like more like two degrees Celsius.

David Roberts

And that's on the timescale of the aerosols going away, like by when?

Ye Tao

Okay, so the fraction that will be added when aerosols fall out, the 1.2, 1.3 watt per meter squared, that fraction, half of that would be realized very quickly, within a couple of years. So recently, I gave a presentation summarizing a dozen peer-reviewed papers that came out since the first batch of COVID lockdowns. So COVID, despite all the inconvenience it created and all the havoc it created, offered climate science a rare opportunity to really assess and confirm this warming that's hidden by aerosols.

David Roberts

Right. Because we stopped emitting them pretty abruptly.

Ye Tao

That's right. And we know exactly when the measures or rules were put in place. So it's a sort of very controlled experiment.

David Roberts

Right.

Ye Tao

And there's a lot of most paper, I think all the paper, experimental measurements confirm that, say, in the area of East Asia or China, there was temperature increase over land of about 0.5 degrees just over the very short weeks to months of the 2020 lockdowns.

David Roberts

Right. That wasn't even a year, right. That was a matter of months. And there was an immediate rise in heat in the area.

Ye Tao

Yes. So when we talk about this global average temperature increase, you have to average over the oceans and land. But of course, the primary driver in that process will be land, because it's the one that's the lowest heat capacity. And that's a component that also responds most instantaneously to an increase ramping up in heating power. And then, this land temperature increase will then drive atmospheric circulation patterns, which bring the warm air to the oceans and also bring the oceans up to temperature. So it's to be expected that the fastest response component is land surface temperature.

David Roberts

Right. So where does that leave us by 2050? Say we switched to renewables tomorrow and just had the sort of legacy, 1.5 per watts per meter, and then the additional 1.2 that we would get from dropping aerosols out, what temperature, global average temperatures that put us at in, say 2050.

Ye Tao

Yeah, thank you for bringing me back to answering those questions. But now let's remember that the aerosols are masking 1.3 watts per meters squared So essentially, as we decarbonize, we'll lose that component. And now let's just remind ourselves of how much our annual emissions is adding to this heating power. So I'm quoting some presentations, I had to track down the source, but our annual CO2 emissions at about 0.06 watts per meter squared of heating power. So over 20 years, 0.06 times 20 gives you roughly about 1.2 watts per meter squared, which just happens to be comparable to how much aerosols are masking.

So in a very simple model of decarbonization, linear decarbonization, from now until 2040 something, we would have avoided creating 1.2 watt of per meter squared of heating, but at the same time, we would have unveiled or unmasked about 1.2. So the two at this point, just magically happens to balance out, which allows us to have very high confidence of the heating trajectory of the Earth system from now until 2040, 2050s. So the two-degree mark will most certainly be surpassed in that decade. And that will happen regardless of what we do on the emissions front. Because of this coincidence of the annual heating contributed by current emissions and how much is currently masked if we continue to have this emissions.

David Roberts

You never gave me a temperature for 2050. Is three possible?

Ye Tao

In my personal opinion, I think that will be quite difficult to reach due to the thermal lag and things in the system. Like for such a gigantic system, things move slowly. And if you just look at, disregard all the underlying mechanisms, just look at the temperature versus time data, the slope of that changes very slowly. So there's polynomial projections generally tend to work pretty well for these massive systems.

David Roberts

But the point is we are definitely going to pass the threshold we have deemed safe, I guess. Is that the tooth threshold anymore? I don't know if safe is the right way to describe under that, but over it certainly unsafe.

Ye Tao

Yes, we have functionally passed the two-degree threshold that's touted as being safe, and because of this predictable trajectory. And also most people have no understanding of the underlying dynamics and maybe just assume that temperature is proportional to current emissions, then it perhaps enables some very few policymakers who may have a scientific understanding to really perpetuate this, essentially, a lie to the public that we can somehow get temperature under control just based on conventional mitigation. It's not really the case.

David Roberts

Okay, so this brings us around to we need to deal with heat in some more direct, faster way than via CO2, certainly than via CO2 reduction in emissions. So one obvious question is what about CO2 removal? What about direct air capture of CO2? This is, sure you're aware, very hot right now.

Ye Tao

Yes.

David Roberts

Do you think that could accelerate the drawdown of CO2 fast enough to counter this rise in heat?

Ye Tao

No. Before we really start to look at any particular solution, I think we need to really dive and find the core of the challenge, the core of the problem. So the problem is energy imbalance of the Earth system. Meaning there's net power, net heating power coming into our home planet. And we need to be quantitative because this is a very important problem. So quantitatively, the heating power that's heating Earth is roughly 1000 terawatts. A "terawatt" is ten to the twelve watts, which is 1,000 billion. So we have roughly 1 million billion watts heating the Earth system, 1000 terawatts.

Okay. Now we're humans, and we think we can modify our environment, but to do any modification, we need to use our machinery, our technology. And our machinery and technologies are powered by energy. So let's see how much energy we have available. The whole of humanity in 2020 was using a power of 18 terawatts. Okay, so the problem of overheating is 1000 terawatts. And we have 18 terawatts of mostly fossil fuel combustion heat to deal with the problem. What does that mean? That means we need to have a cooling system that's 1,000 over 18 times 100% efficient, which is roughly 10,000% efficient.

So just to put things in perspective, for an air conditioning that most people are familiar with, for every unit of electrical energy you feed it, it can move about three or four units of heat from one side of the wall to the other side of the wall. So it's only a coefficient of performance of three or four. But here, to move heat from inside the biosphere, the atmosphere outside into space, we need a coefficient of performance of 100. So that's drastically more efficient than just any typical technology that we are aware of.

David Roberts

So where does that leave us?

Ye Tao

So that basically means, in order to have a chance of stopping global warming, the particular process that you invent needs to have a minimum theoretical efficiency that's much, much larger than 100. Why is that? Because it's not possible to use all of our energy to just tackle climate change, because most of the energy goes into also feeding the population and keeping us warm. So then the question is — this is an unsolved question and I think we're starting just to discuss answers to this question which is — so realistically what fraction or percentage of the 18 terawatts is humanity able to devote to tackle something like climate change?

So there is no answer to that that I'm aware of. And leading thinkers in these fields have not really been alerted to the importance of finding that number, because the MEER framework is not widely known yet.

David Roberts

That wouldn't be a physical limit, though, would it? I mean, the limits on how much of our energy we're willing to devote to that is not. That'll be a social constraint, won't it?

Ye Tao

To a certain extent, with the assumption that somehow social opinions and the societal trajectory could be arbitrarily curved. But there are underlying mechanisms that we are simply not aware of, or we don't fully understand. And there are also physical limits to how much fossil fuel extraction, let's say, if that's the power that used to solve this problem, and how quickly we can build solar panels. There are some kinetic barriers to how much we really can. But of course, these things needs to be investigated in the process of finding how much energy really we are able to devote to this process.

But just as an analogy, people have calculated what fraction of current power needs to be devoted to renewable infrastructures to fully decarbonize it, become running mostly on renewables by say, 2050. And that figure falls between, say, 0.5% to maybe 5% of current total energy consumption. But even that single-digit percent investment seems to be difficult at this point. And most of the world is not aware of this Earth energy imbalancing problem that will guarantee global warming yet. So it's not even in discussion. So we would be very, very optimistic in thinking that somehow we could manage to put, say, 5% of our energy consumption to tackle this heat problem or global warming at its core.

So that corresponds to roughly one terawatt of power out of 18 terawatts. And if that's the case, we need what we call a heat rejected on investment or cooling return on investment. We need this ratio to be a couple of 1,000 or 2,000.

David Roberts

Right? How do you get the most heat out of the system per ...?

Ye Tao

Unit input in energy and the materials.

David Roberts

Per energy expenditure.

Ye Tao

But it's easy to measure things, well, it's possible to convert things at least to the energy base on first inspection, before you even consider the material analysis. So we can apply this framework, or this minimum requirement criterion, to analyze, say, the likes of carbon capture, direct air capture, and won't find that such methods are short of what's required by an order of magnitude or more. Which basically means if we were to invest all of our energy consumption, 18 terawatts, into the process, we would barely really just manage to capture, contemporaneous or contemporary emissions.

And it's obviously not possible. So it's essentially an industry that's created that can turn a profit on small scale, but its capacity is only capable of, in the very optimistic sense, address its own emissions in running the process and creating all the absorbents and all the factories that's needed to make it run. So it's a very ideal exemplification of capitalism, basically creating a need out of nothing and asking consumers to pay for it and branding it in dishonest ways.

David Roberts

Okay, we got to get to the mirrors eventually, so I want to cross a few other things off the list. This is our framework. We have X amount of energy available to tackle this problem. And the way we need to approach it is: how do we get as much heat out of the system as possible per unit of energy we expend? What about these other geoengineering ideas? Like what about sulfur particles in the atmosphere, or cloud seeding, or kelp? Have you gone through the geoengineering catalog and tried to figure out what can and can't reject the most heat?

Ye Tao

Yes, we have basically done a more or less comprehensive analysis of all the proposals out there. And I'm also part of several discussion groups online that the members of which are basically leaders and principal investigators in different startups and companies, or nonprofits, each fostering different techniques and approaches. For example, Stephen Salter is a professor, retired professor, from University of Edinburgh, that I visited actually in person, studied vetting for two days to really understand the latest thinking and design for marine cloud brightening. So I can say that I have a pretty comprehensive understanding of the limitations and capabilities of different approaches.

So you asked about solar radiation management, and the only two that's currently being talked about include stratospheric aerosol injection, and there's a marine cloud brightening.

David Roberts

This aerosol injection, which let me just interrupt briefly, the aerosol injection, which would ironically be furiously attempting to replace the aerosols that are falling out of the atmosphere as we're reducing coal burning.

Ye Tao

Yes, it's an attempt to perform something similar, but there is important distinctions. So the aerosol that we create from coal burning, they don't go very high up in the sky because they are sourced at the ground, and they're transported by atmospheric circulations in the troposphere. So troposphere is the lower part of the atmosphere, up to a height of about 10 km, so roughly 10 miles in some cases, and thinner on the poles, but it's roughly flight altitude, cruising flight altitude, and much above that, it's called the stratosphere. So the two layers don't really mix very well, which means when you inject particles in the lower part, they fall up much easier, so they're less stable.

But if you put things up high in the stratosphere, they stay up much longer on the order of a couple of years, maybe sometimes more. So one of the thinking about why inject into the stratosphere is because it makes the particles more stable, which means you don't have to inject all day, every day, 24/7 because the next rainstorm or precipitation events would have wiped out all your reflectors. So that's why people are thinking about putting them up in the stratosphere. The problem is that we do not have a full understanding of the chemistry or physical transport or nucleation, cloud nucleation, properties of the different particles that are being proposed.

We do know that sulfuric acid nanoparticles, or droplets, will contribute to ozone depletion. So that's one known risk. What's not really been studied fully is when these particles eventually fall out. So the way they fall out is they get injected, say, in the tropical latitudes, and they get transported by stratospheric circulation to the poles, and they ring out over the poles. So when they ring out over the poles, they could potentially seed cloud over the poles. So if it's the summer, polar summer, then great. They're promoting some cloud formation, so shielding part of the polar water from being heated up by sunlight.

But because the residence time is over a couple of years, so they will also potentially fall out during the winter. And when they do seek cloud during the winter, it's like the cloud acts as a blanket. So they prevent freezing. They could potentially prevent freezing of the Arctic during the winter. So clouds, you can conceptualize that basically as a barrier for energy passage. So which way it's impeding the flux of energy depends on the net vector, or where the flux is going. So in the summer, there's more coming down, so they have a cooling effect. In the winter, there's more energy going out by radiation than they would have a keeping warm, warming effect.

And since we do not have the microphysical understanding fully of cult formation over the Arctic, in the event of a large quantity of aerosols raining down there, we do not really actually know the sign of the impact, local impact, in the Arctic.

David Roberts

And that's, I think, a specific version of a more general point, which you said before, which is just, "We don't understand the risks of these things well enough to be doing them." So this is what sort of sponsored your search for a simpler, more direct version of geoengineering. Which brings us to the mirrors. Your proposal, to put it as simply as possible, is to cover a decent swath of the earth's surface with mirrors, and the mirrors will reflect solar radiation back out into space. And with sufficient mirrors, we could reject enough heat to bring the global average temperature down into a safe range, even if CO2 remains high and even rising.

Is that a fair summary?

Ye Tao

Yes. The idea for using mirrors, which is a local light management, or reflector device, is very important because these challenges are interconnected. Shortage in food that's coming down the line and the droughts. And local communities are the one that's bearing the brunt of the impact. If we can not only tackle the global problem, but primarily have a very strong local impact, then it's a process that can be tested on small scale, and that can be potentially implemented out of the volition of the local population communities and in a naturally organically, democratic way in its testing.

David Roberts

Let's talk about then what would I mean, obviously, the global effect of reducing global average temperatures is to everyone's benefit, but what would be the local effects that you could sell a local population on, of creating big fields of mirrors?

Ye Tao

Okay, so we have preliminary data from the summer season of 2021 to put some numbers on the expected impact. So in our very small mirror field in New Hampshire, Plymouth, New Hampshire, during the months of July, which happened to be very wet. Despite high soil moisture during the measurement period, we could measure up to ten degree Celsius temperature reduction in the regions underneath a single mirror, that's as small as 2 by 2 feet.

David Roberts

If you're talking 2 by 2, the directly shaded area is going to move around all day. So it reduces temperature in the whole area of soil?

Ye Tao

That's right. So the shade, as you mentioned, it swipes over a region which is on the order of five or 10x the surface area of the mirror itself. And over that region, you can have order degrees of cooling at the surface. And a few degrees can really make a huge difference between complete crop failure to an excellent harvest. So, for example, for every day that your crop spent over 30 degrees Celsius, you can expect a drop of about 1% in yield. And studies generally have only analyzed data that's not too many degrees above 30. But this year, for example, in India and Pakistan, people experienced 40, 50-degree days over weeks.

So these extreme weather events and their impact on crop, we just don't really have enough data to really put a number on it. But most likely it's not going to be linear. So maybe for every degree over 40, it's more like 10% drop or even more. So if you can somehow manage to reduce local field temperature by five degrees to ten degrees, we can more or less locally just delay these devastating impacts.

David Roberts

So is the idea that the mirrors are ... tell me what this looks like. Are the mirrors over the land on, like, stilts or something? Or how would you, I mean, if you have a field of crops, where are you putting your mirrors to get this effect?

Ye Tao

Yeah, so those parameters are currently being investigated in a more extended field experiments in Concord and Plymouth, New Hampshire. So we're looking at the impact on soil temperature and moisture and the local air temperature, as a function of a coverage pattern and the coverage of fraction. So we're looking at between 5% coverage, up to 25%, 30% aerial coverage. And just based on how the Earth rotates, we know that the shadow scans along the East/West axis. So we are looking at configurations where we have columns of mirrors lined along the North/South axis and playing around with parameters of inter-column spacing, and also a bit inter-row spacing, at this moment.

You can have various designs for field-applied mirrors. You can have each, say, square or rectangular mirror supported by a single rod that's planted into the soil. So that's what we're using for its simplicity in our experimental measurements. But of course, you can also have an array of rods between which you can tie even a flexible polymer based reflectors, which would save how much glass mirror you need. And if different materials become limiting, then you can use ones that are readily available.

David Roberts

Isn't this something that PV people are currently investigating? I mean, agri-PV or whatever the heck they call it. Agrisolar?

Ye Tao

Yes, agrivoltaics.

David Roberts

Yeah, agrivoltaics. They're busy investigating these same questions, aren't they? I mean, it's somewhat similar.

Ye Tao

Yeah, there are similar questions that are being investigated, with the important difference that when you put PV panels, while you can provide local soil cooling and shading, you're actually increasing how much heat is produced inside the atmosphere. Because PV panels are extremely light absorbing and dark, so it would create a higher air temperature. So in regions that are already stressed by air temperature, if the temperature is the main stressor rather than moisture, then it would become a net negative sooner. In the case of mirror, the shading impact is similar, but it also has this air-cooling impact.

David Roberts

Right. And I'm trying to get a sense of scale. I don't know how to put this together in my mind. How much coverage by mirrors are we talking before you have a regional effect? Do you know what I mean? Like, if I'm on the next farm over, do I ever get cooler? Or are these strictly local effects? If we had half our square footage of our town covered in mirrors, would the entire rest of the town get cool?

Ye Tao

Yeah, there's actually some data, not from this field, but from the field of scientists, engineers trying to address urban heat island effect that provides some hints to the length scale, correlation length scale. And if you have a neighborhood that's significantly brighter than the neighboring one, then the cooling effect extends to, on the word of quarter mile, hundreds of meters around this area. So you can create essentially what are local oases.

David Roberts

Right?

Ye Tao

So that's the other interesting idea of mirror of this local solution because it potentially can create these local environments that are still habitable, even if the global average temperature has increased way beyond what's sustainable.

David Roberts

Right.

Ye Tao

So it's almost like essentially oasis in a desert. And I think it's an open scientific and engineering question as to whether such oases could be created and on what length scale, and eventually, like, what length scale of these habitable islands do you need to enable local biodiversity to persist? So these are interesting, multiscale, interdisciplinary questions that potentially we could answer once the mirror framework becomes mainstream.

David Roberts

And you envision mirrors out in fields or on top of buildings or over parking garages, or all the above?

Ye Tao

Yeah, all of the above and more. So another project we have ongoing this summer is to look at water-saving potential when you float mirrors on top of water bodies, let's say reservoirs. So Deutsche Welle, the DW, German television, just released a video, or documentary, about heat, the recent heat stress in Pakistan and India. And they mentioned that about 60% or 70% of the fresh-water gets lost during a distribution system because they're flown in, like, canals or aqueduct that's open top. So just imagine if we had covered that with mirrors to reduce the evaporative loss and conversion to latent heat, we could potentially significantly alleviate urban water stress.

And our experiment from last summer already qualitatively demonstrated that water saving impact. And this year, we have added new string age sensors to monitor the weight of the little bins and buckets that we use to simulate a water body to more quantitatively understand how much water we can save in the process. So it's saving water and also cooling the planet at the same time. So it's like multiple benefits.

David Roberts

Here's another question I'm sure you get from every audience you talk about this with. I'm trying to imagine a city or just any large swath of land that is close to completely covered in mirrors, and it just seems like flying over that would be dazzling. I mean, I don't know if there would be heat reflecting up or light in people's eyes, or is there any danger at all in covering the ground with mirrors in terms of, like, the airspace above it?

Ye Tao

Our experimental site in Plymouth, New Hampshire is right beside the municipal airport. And the administration really looked into the problem and concluded it's not really a problem. Why is that the case? So even in the highest coverage that we would realistically deploy, which is around like say 20% of land surface area, we at most would increase basically ground albedo by about 0.1 or 10%. So what the pilot would actually see is, okay, there is the sun in the sky which is providing say 100% of the downwelling short-wave radiation. And then from this mirror field from below, it would add maybe 10%, 20% percent of what's coming from the top-up.

And because the mirrors are not going to be precisely controlled in direction up to 0.001-degree precision, the different beams of light from each individual devices will go in every which direction, more or less scrambled. So the pilot will not really see a coherent image or reflection even from the mirror field.

David Roberts

So the beams won't come together at any point. So there wouldn't be any heat either, I guess then.

Ye Tao

Yeah. So there's no concentration of radiation energy in space, so no birds will notice it. So we have watched the birds landing on these mirrors, and also turkeys going through the fields. They are not really concerned because to really get them to point in the same point demands a lot of engineering, and that's the focus of many different companies, just to how to create such focal point reliably.

David Roberts

So I've talked with several of them. Well, let's talk about the simplicity, then, because that brings us to the subject of materials, which is a huge piece of this. One of the things you say, one of the sort of premises of the project is, "We need to find a solution that can reject as much heat as we need to reject using materials we have available to us, currently." So that sort of excludes any sort of fancy fabrication or engineering or rare materials or scarce materials. So talk about what mirrors are made of, and how much of that stuff there is.

Ye Tao

Okay. So that's a very natural flow of things. So first of all, we have to establish that energy-wise mirrors can provide that leverage. We won't go into details today, but yes, we have established that that's feasible. And next is do we have enough material to construct all of them? So the initial stages of the project we had focused on considering soda lime glass as the main material that goes into both the supporting structure and also the planar reflector, because the technologies already exist, and we essentially buy from commercial suppliers, currently, for our field experiments. And the advantage of glass in this application is that they essentially don't degrade.

And the ones that we have also even survived minor hailstorms from last year. So we are pretty confident — and also snowstorm. So we're pretty confident that, in most parts of the world, these things can last for decades, at least to centuries.

David Roberts

The glass can last. But isn't the reflective surface somewhat more vulnerable?

Ye Tao

Oh, so we just thinking about that problem, we have designed our prototype to be such that the reflector layer is sandwiched between two glass layers, top and down, so that they are protected by impenetrable glass from chemical intrusion. Of course, there's still some work to be done for edge ceiling, but that's a minor engineering material science development that's totally manageable, given enough resources.

David Roberts

And you're just talking about "glass" glass, right? Plain old glass. We're not talking about any special bulletproof or industrial or whatever.

Ye Tao

No, we're just relying on solid lime glass, which of course is not as clear or transparent as, say, high-quality, pure fused silica. But for the extra, say, two 3% transmission, you would have to increase your expenditure by orders — that doesn't make sense. For something like this, we just use what's mostly readily available in abundance — so the lime glass.

David Roberts

And there's no conceivable shortage of lime glass?

Ye Tao

No, actually, that's something I need to point out. So our initial thinking was, "Yes, we do have enough reserves in soda lime glass to implement the full project out of glass, and to basically stop further global warming. We can do that. We do have both the energy and the material to do that." The energy consumption for a all-glass framework is 3% of global energy consumption. So which is, again, in the slow single digit, which is optimistically feasible.

David Roberts

Annually?

Ye Tao

Annually ... well, I mean, it's a power consumption, so it's 3% of annual energy consumption.

David Roberts

And you're talking about just manufacturing mirrors.

Ye Tao

Manufacturing glass and mirrors, and transporting and implanting them. Because most of the energy is used in the melting process, the rest is basically negligible because the melting process is the most energy-intensive step. So the bottleneck for a all-glass solution is not in the reserves for making the material, or in the energy needed to power its manufacturing, it's actually in the speed at which we can make glass. So it turns out that we need slightly more than an order of magnitude higher annual glass output than currently exists, in order to do this. So that's a huge problem.

David Roberts

Right.

Ye Tao

So that's why we started recently to think, "okay, we cannot really expect humans to really coordinate to such an extent that we just decide to ramp up one particular industry by ten times. What — can we do something in the meantime to still keep the project going and also keep it readily scalable?" That's when we start to consider replacing the planar reflector part, using reflectors based on PET, polyethylene terracethalate, thin film plastic. The advantage of this material is that you can make thin films that are very thin but still tensile, quite stable over multi feet length scales, and they're stable even down to thicknesses of a few microns.

So when there are a few ten of microns, they are already very robust. So even though the energy intensity for making these polymers is roughly one or two orders of ... higher than making glass for the same volume, but because you can really make the polymer film is much, much thinner than you can make glass. Glass needs to be a few millimeters in thickness to be stable, whereas these can be 100x thinner and still be stable. So the energy penalty, by a factor of ten, is more than compensated for, by using less material of the polymer.

And these polymers, they degrade mostly via oxidation and weathering due to UV radiation and the photo-activated processes in the atmosphere. But if we can protect the underlayer using the reflector layer, that should largely attenuate the process. So there is the possibility, but enough research to make these films much more environmentally stable. And if they can last for more than five years, based on our calculations, the system would be able to deliver the energy rejected or cooling return on investment ratio of 1,000 or 2,000 that's required for the process to be viable.

David Roberts

Yeah. And I would think if we globally decided we suddenly needed to be manufacturing enormous quantities of reflective surfaces, I would imagine there's lots of innovation to be had there, just in terms of materials, in terms of scale and processes and everything. If it ever got going on that scale, I'm sure there would be ways to bring down material costs.

Ye Tao

Yeah, I'm sure. So we need to mostly just alert people to this seemingly simple but actually quite versatile framework. And we certainly have enough pet for the process. So we have been looking into how much goes into landfills, and it turns out that what's currently going into landfills, which is roughly 20 megaton per year of PT plastic, that amount is more than sufficient to implement the whole project. And how much aluminum cans that are going to landfills is 7x more than what's needed to implement the mirror framework. Right now. The only remaining puzzle is still this glass part, because it's still our understanding that the part that interfaces with the soil needs to be made of glass for chemical durability and zero-emission requirements, and currently rejected or buried glass bottles, wine bottles, champagne bottles, and container bottles is at 150 megaton per year. And that's only sufficient for about 10% of mirror needs.

So finding a sustainable material, for making this support for the reflectors, is a current challenge. So we're looking at other systems, like, maybe pressure-treated bamboo that's more durable, or some sort of composite that combines recycled, upgraded, reused materials. So that part is an ongoing research, but we're getting very close to being able to finance the mere framework in terms of energy material, using what's currently discarded, the resources in landfills.

David Roberts

And you mentioned too, moving manufacturing over to being — because currently, I guess, glass manufacturing is mostly fossil fuel. You've talked about trying to drive that with solar.

Ye Tao

Yeah, that would be quite ideal, and it's certainly feasible. So it's already been demonstrated in 2018 by research group Paul Schur Institute PSI, close to Zurich in Switzerland. But the solar program there got shut down like a couple of years ago for reasons that I don't understand. But it's certainly possible, and if we can harness that — but anyways, I don't think energy is anything of a concern. What's needed is really policy and understanding. Like methane emissions, fugitive methane emissions from landfills, more or less, is sufficient just, if properly channeled for furnaces to make glass for the mirrors.

That alone is sufficient for the process. So it's a combination of if we can solve several problems at the same time.

David Roberts

One thing that I wanted to ask, sort of straightforwardly, is it seems like one of the implications of this research is that it is better to put up a mirror than to put up a PV panel. And it is better, as a matter of fact, to manufacture and put up mirrors than it is to manufacture and put up renewable energy. And you could even say that if we rejected enough heat with mirrors, CO2 would not be nearly as urgent a problem, and transitioning from fossil fuels to renewables, would not be nearly as urgent of a problem. Is that all fair?

Ye Tao

No, that's not correct. I think the conceptual distinction to make is that energy provisioning and global warming are two separate challenges. Energy provisioning is try to make the 18 terawatts that we're currently using carbon neutral. Global warming management is how to get rid of the 1000 terawatt of heat. So they're on completely different scales of challenge. In a sense, the renewable energy challenge is even easier, I guess, because it's also like at the more advanced stage of discussion compared to the global warming excess heat management problem. Again, here there's a natural tendency to link the two problems because energy provisioning created the problem, therefore, we have to solve the global warming problem by addressing energy provisioning. But that's not conceptually correct.

David Roberts

Well, I guess what I'm wondering is if we have this knob, this relatively cheap knob that we can turn to turn down heat, why do we care if our energy provisioning is carbon intensive?

Ye Tao

Well, I mean, there is some limit, eventually, of physiological intolerance to CO2 that we know. So yes, it's a few decades down the line, but we know that the fossil fuel industry has been successful in the past decade. So who is to say that they won't continue to be successful, if we don't counter them with as much determination as we have shown, at least in the activist and academic fields. So we certainly need to decarbonize that. There's no question about that. So these are two separate problems.

David Roberts

Got it. And so as a final question, and thank you for sharing so much of your time. I guess I'd like to know — all this right now is really early. I mean, most of it is just sort of noodling and thinking about it and conceiving and trying to model it and work out the math. How do you envision, or do you envision, it starting to translate into reality, and then I guess, secondarily, how big would it have to, I mean, how much surface area are we talking about before we start feeling global temperature effects from it?

In other words, like how big of a head of a steam does it have to get before we start getting global payback from it?

Ye Tao

To more or less keep the climate at current levels, we need to implement these refactors over maybe 15% of currently used agricultural land.

David Roberts

That's a lot.

Ye Tao

And it doesn't have to be just land that's currently cultivated. Yes, it's a lot. However, we remember that when you put them into the land you most likely will actually increase per area yield. Then it feels more manageable. And because these agricultural fields are already snatched surface that's highly engineered, there is a little concern for biodiversity impact. And if you can provide also local cooling shade and more moisture, it might actually foster some local rebound of insect population and the soil microbes. And it's also entirely possible that at high enough coverage, one could expand arable land into currently area that's currently too hostile for agricultural work.

David Roberts

Like de-desertification? Wait, there's got to be a better way to say that.

Ye Tao

Well, yes, it would contribute because water is usually the limiting resource. So in some borderline regions, where if you just had a few on average half a millimeter per day of net water accumulation, which could be afforded by the demure rays, then you could convert some of these areas into new habitable zones. And there's evidence for that in megaprojects taking place in China, both under the concentrating solar power plants and also their large-scale PV fields. That previously barren land is now producing grass and becoming grassland, that sheep herders are leveraging and duck herders are leveraging to produce protein for the local population.

David Roberts

What about the economics? We should mention that MEER is a non-profit and run by volunteers, and it's all open source, and this is all — nobody's going to make money from all this. But at the same time, it's hard to imagine something spreading over the entire globe unless it makes money. So is the effect on, if I'm a farmer, is the effect on my crop yield sufficient to pay for the mirror? Do you know what I mean? Would it be an economic transaction for me, or is there an element of government needed, or is it philanthropic in the end, or is there an economy to be made here?

Ye Tao

So we have not done the economics assessment for that problem. But it's something that we have thought about and will performing in the future, mainly because we have not fully obtained the full impact of the parameter space of moisture and temperature and air temperature perturbations. It's only when we have those figures can we then look at the growth functions of different crops and their light requirement, moisture requirement, to start performing that analysis. So our ongoing experiment this year and next year in the field to get those very basic radiation perturbation temperature moisture data is quite necessary to enable that assessment.

But we do have precedents that's already in the field. Many people use, or farmers, use shades or like sort of greenhouse, but really structures covered by partially transparent white plastic in order to reduce how much light arrived at our crops. Because in some most lower latitudes, below 40, solar noon is basically too intense for most plants to survive, really, especially single canopy crop field. So naturally, there's a need to reduce how much light comes down. And farmers have been willing to buy these plastic-based sheeting to cover their crops, and we don't expect the mirrored version to be much more significantly, more expensive.

So, for example, if you look at PET sheeting on Alibaba before and after metalization, metalization is the process of putting on thin layer of metal to make it like a mirror. The prices differ by maybe 10%, 20%, because most of the cost comes from the polymer production and the film manufacturing, by process of thermal and blowing them and cutting them and rolling them. So it seems like just at a qualitative level, changing the current partially transparent white shading to a reflective film, maybe with different ways to put them up, shouldn't be a huge change in what some farmers are already spending to keep their land arable.

David Roberts

So you can imagine a market, and I guess also it's obvious, but worth pointing out, that heat solutions, solutions to heat are going to be much more in demand in coming years than they are now. So I imagine the problem of shading crops will become more acute as time goes on as well.

Ye Tao

Correct.

David Roberts

And people will be looking for solutions.

Ye Tao

Yeah, and also not only heat protection for crops but also for humans. And one of our projects is a humanitarian project trying to deliver these affordable mirrored sheets, or mirrored tiles, for implementing on roofs to help people in Pakistan and India, and parts of Africa, so that they can actually survive during these extreme heat events.

David Roberts

Right. I would imagine it would do an enormous amount to just keep a single structure cool. I mean, that's like life or death difference.

Ye Tao

Yes, a couple of degrees. Sometimes it just said one extra degree. That's really the last straw that crushed the camel.

David Roberts

Alright, well, thanks for coming on and talking about this. It's fascinating. So what's the next step? You guys are doing some early research. Is there next big milestone?

Ye Tao

Next milestone is, basically, include getting more concrete and precise data in the field and also demonstrating or testing cooling in urban heat island settings, and more or less just an educational effort. Because even among people working in this domain of climate mitigation, only a very minor minority are really scientifically trained, and engineering trained, in a multidiscipline fashion that they are able to think from this more top-down perspective. So sometimes people are really excited about their own projects, for example, carbon capture, that they know all details about how the sorbent works, the kinetics of those processes, but they have not had the chance to really zoom out and see, "whoops, even if everything were to work 100%, as I expect, it's still not enough to really tackle the Earth energy imbalance."

So really teaching people about what's the core problem, we're trying to confront, is one of the future focus over the next year. So we'll be updating our websites with these educational texts. So a lot of time is actually spent trying to translate university-level basic science writing into 8th-grade compatible writing material. And sometimes it's creating more time sync than we like to spend.

David Roberts

I know that struggle. Alright, well, thanks so much. Thanks for taking the time, and I'll be following the project.

Ye Tao

Thank you.

David Roberts

Thank you for listening to the Volts podcast. It is ad-free, powered entirely by listeners like you. If you value conversations like this, please consider becoming a paid Volts subscriber at volts.wtf. Yes, that's volts.wtf, so that I can continue doing this work. Thank you so much, and I'll see you next time.