Volts podcast: Dr. Ye Tao on a grand scheme to cool the Earth

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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transcript)


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transcript)


Text transcript:


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


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