“Crazy” climate tech: enhanced rock weathering, solar geoengineering and direct air capture


One day I’ll know how to write shorter titles instead of a list. It is not today though. 

As the title suggests, we are going to zoom in on three climate techs: enhanced rock weathering, solar geoengineering and direct air capture. We will examine whether:

  • these technologies can become important levers to fight against climate change and environmental degradation
  • they are just distractions from the more serious solutions that no one wants to address because they would ask us to change our way of life quite radically. 

Before we start, I think it is important to remind ourselves that technologies are one of the levers in tackling climate change, biodiversity loss and environmental degradation, but they should not be the one and only solution, nor the most important one. 

As we have learnt throughout recent human history, one technological solution can potentially lead to many unwanted side effects that will need more technological solutions to fix the messes

One example could be the introduction of invasive Asian carp in the Mississippi River. They were introduced to the U.S. in the 1970s to “control algae, weed, and parasite growth in aquatic farms and as one form of sewage treatment”. Yet these captive fish escaped into the Mississippi River basin, reproduced at an incredible speed and – this may sound far-fetched – they ate everything in their way.

As illustrated in the book Under the White sky (Elizabeth Kolbert), to fight against this invasive species, the authorities and the U.S Army tried many solutions such as putting up fishing nets, poisoning the water, and throwing flying knives to kill the carp when they jump out of the water to clear debris from their gills.

Eventually, they settled with electrifying a part of the river that leads to the Mississippi basin. The science here is that when a fish swims in this electrified water, “its nose is experiencing one electrical voltage, and its tail is experiencing another. […] It’s the current flowing through a fish that will shock them or electrocute them. So a big fish has a big voltage difference from its nose to its tail. A smaller fish doesn’t have that much distance for the voltage to cover, so the shock is smaller. […] The good news is that Asian carp are very big fish.”

In other words, “in order to fight monsters, we created monsters of our own.”(*wink at Pacific Rim*)

electric barriers in the Mississippi river
An electric barrier built across the Chicago Sanitary and Ship Canal (Source)

This does sound like a desperate measure to protect the native ecosystem of the Mississippi basin. Indeed, there are a lot of signs put up to protect humans wandering around that electrified part of the river. One must wonder what would happen to other animals who cannot read those signs…

Alright, let’s go back to climate tech. 

What is climate tech? What is cleantech? What is Greentech? What’s the difference between them?

meme climate tech, clean tech, gren tech, ecotechnology
Climate tech? Cleantech? Greentech? Eco-technlogy? WHAT?

Simply put, “climate tech” is any technology used to mitigate global greenhouse gas emissions

Meanwhile, the scope of “cleantech” is a bit larger: it refers to any technology that helps reduce environmental damage or improve environmental quality. “Greentech” and “eco-technology” are used as synonyms of “cleantech”. (By the way, cleantech and greentech must be written without the space so that they look cooler).

With this in mind, in this article, we will only focus on technologies that are labelled as climate tech, used to reduce global greenhouse gas emissions. Indeed, I have to stress it again here: the most efficient lever to reduce greenhouse gas emissions is not to emit them in the very first place, by phasing out fossil fuels, revamping agricultural and industrial systems, uncoupling economic growth with resource consumption and emissions, etc. 

Alright, brace yourself, we will look into crazy, mind-boggling climate tech, and you’ll be able to judge for yourself if they are going to help us to “cancel the apocalypse.” (*wink the second time at Pacific Rim*)

Enhanced rock weathering: putting rock powder on a large surface to suck up emissions

If this is the first time you’ve ever heard about enhanced rock weathering in your life, fret not, it is totally normal. This is such a new possible technology and theory, yet it is based on a process as old as the Earth itself: the carbonate–silicate cycle

This illustration shows you how this process looks:

I’m no chemist, so there is no way I’m gonna be able to explain this illustration to you and to myself. So I’ve made another: 

A simplified version of the carbon-silicate cycle
A simplified version of the carbon-silicate cycle (Source: Waste is Failure of Design)

Basically, silicate rocks are exposed to the weather and broken down into clays, soils and smaller rocks. These things react with CO₂ in the air as well as water to produce new minerals such as bicarbonate (HCO₃⁻). And these minerals go out to the rivers and oceans. 

How much CO₂ can the rock weathering process sequester? So far, we know that “the weathering of silicate rocks is a net sink for atmospheric CO₂ (Berner, 1992)”, which means “one mole of CO2 is being sequestered for each mole of calcium silicate mineral weathered.” 

This is a natural geochemical process that has been here since the dawn of time, and it can go on for thousands or millions of years. 

Yet, we don’t have thousands of years to wait on the warming planet. Scientists have found ways to cut this period to two years: grinding silicate rocks into a fine powder, thus increasing its surface area and its contact with CO2.” That’s why the technology is called “enhanced rock weathering”, in which we essentially accelerate the carbo-silicate cycle

So, where are we going to put this silicate rock powder? On our farms! 

I’m sorry what?

Research has shown that this powder could improve agricultural yields, improve soil health and replace synthetic fertilizers. Mineral nutrients such as calcium, potassium and magnesium can help create healthier soils. There is nothing new under the sun: farmers have been amending soil with rock minerals for centuries.

Another application of enhanced rock weathering can be used in the case of soil degradation from acid rain, as shown in a 12-year study conducted in a New Hampshire forest. Acid rain, as discussed in a previous article on agriculture, happens when nitrous oxide (N₂O) from excess nitrate synthetic fertilizers meets with sulfur dioxide (SO₂) emitted from the use of fossil fuels. Applying dissolved silicate and calcium could help alleviate the acidification of the soil.

Here’s the demonstration of the practice in the world’s largest experiment (20 hectares). Initial results suggested that “adding basalt and wollastonite, a calcium silicate mineral, increased corn yields by 12% in the first year”.

What if this rock power goes to the river and into the ocean? Does it create any weird effects? On the contrary, just like in soil, bicarbonate ions in the ocean “make the water less acidic”, which can help reduce the effect of ocean acidification. Indeed, a small amount of rock powder is not enough to reverse the dire situation of ocean acidification we face today, but at least it does not add up to the problem. 

So far, this enhanced rock weathering sounds like magic. I understand that you need to hear the downside. So, what is the potential of rock powder if we scaled it up to a global level? It is estimated that “adding 10-30 tonnes of silicate per hectare per year to two-thirds of the world’s most productive cropland could take 0.5-4bn tonnes of CO2 out of the atmosphere per year by 2100.” 

The other problem is, the world emits about 34bn tonnes of CO2 per year. Indeed, we can’t expect rock powder to absorb the whole of our yearly emissions, but when comparing 0,5 to 4bn tonnes sequestered vs 34bn tonnes emitted, something doesn’t quite measure up. 

There are also several logistical concerns regarding enhanced rock weathering:

  • Grinding rocks into power requires a LOT of energy. Ideally, renewable energy should be used to grind rocks to minimise extra GHG emissions. 
  • Transporting the powder to the site also requires energy. As seen in the video clip above, the powder is spread using a truck using fossil fuels. Cleaner transportation methods must be studied to not emit extra GHG emissions.
  • According to a recent study by a team of German scientists, to remove 1bn tonnes of CO₂ through “enhanced weathering”, approximately “3bn tonnes of basalt would have to be mined, crushed and transported.“ And while this is a very large amount of rock to mine, grind and ship, the authors noted that “it is less than global coal production, which totals 8bn tonnes per year.”
  • Also, the cost estimates of this technology are uncertain at the moment, but so far it is estimated to be $52-480 per tonne of CO2 sequestered, more expensive than $39-100 per tonne of CO2 sequestered by bioenergy with carbon capture and storage (BECCS), cheaper than $125-335 per tonne of CO2 sequestered by a large-scale direct air capture plant. These costs are all projected to fall in the future. 
  • I couldn’t find the price of enhanced rock weathering as fertilizers to compare with that of synthetic fertilizers (the latter, by the way, has doubled since 2021 and this may promote sustainable ways of growing crops). I’ll update this once I find the relevant research. 

So, if you were a policymaker or a green investor, will you invest in enhanced rock weathering as a potential climate tech? 

Don’t decide yet, you still have a couple of other choices.

Solar geoengineering: let’s engineer the hell out of the climate crisis

Please take a small break and drink some cold water, before going on yet another wild ride of climate tech. 



First of all, it is important to learn about a notion called volcanic winter

  • when a volcano erupts, it put sulfur dioxide (SO2) into the stratosphere
  • this sulfur dioxide gets oxidized on the scale of weeks to sulfuric acid (H2SO4)…
  • this sulfuric acid starts making particulate matter, aka concentrated sulfuric acid droplets, usually smaller than one micron…
  • these droplets – or aerosols – stay in the stratosphere on a timescale of a few years, and they scatter sunlight back into space…
  • the result is lower temperatures, fantastic sunsets (and on occasion, famine). 

So, if we fixate on the “lower temperature” part of this volcanic winter process, we are stepping into the territory of solar geoengineering, which seeks to “reflect a small fraction of sunlight back into space or increase the amount of solar radiation that escapes back into space.“

There are a couple of techniques, as presented below:

Solar climate intervention methods
Solar climate intervention methods (Source)

Let’s go through these techniques one by one: 

1. Surface albedo enhancement

Proposals for this technique span a wide range, from growing crops that reflect more light or engineering crops to reflect more light, to clearing boreal forests in snow-covered areas (which means less forest!); from covering large desert or ice areas with reflective materials to whitening mountaintops and roofs with white paint (?!).

2. Increasing the reflectivity of marine clouds

According to this scheme, a fleet of ships (very likely, run by fossil fuels) would be dispatched to the Artic Ocean to shoot very fine droplets of salt water into the sky. The salt crystals are theorized to increase the cloud’s reflectivity, thus reducing the amount of sunlight striking the ice. 

Shooting salt particles into the cloud
Shooting salt particles into the cloud (Source)

3. Increasing the amount of stratospheric aerosol 

This means: an aircraft goes up to the stratosphere and scatters tiny reflective particles such as sulfate aerosols, calcite, calcium carbonate or even diamond where they could reflect a small fraction of sunlight back into space

Concept art for a SAIL - a Stratospheric Aerosol Injection Lofter Aircraft
Concept art for a SAIL – a Stratospheric Aerosol Injection Lofter Aircraft, in the thread r/BiosphereCollapse on Reddit (Source)

Yet, since these particles could drop back down after a couple of years, they’d need constant replenishing. If the SAILs (Stratospheric Aerosol Injection Lofter Aircraft) flew for a few decades and then stopped for whatever reason – a war, a pandemic, or unhappiness with the results, the effect would be like “opening a globe-sized oven door”. 

All the warming that had been masked would suddenly manifest itself in a rapid and dramatic temperature rise, a phenomenon that’s become known as “termination shock”. I don’t understand the chemical explanation of this phenomenon, but it sounds terrifying with an already-warmed-up planet. What I do get is that once deployed, this process must be continued at all costs. That sounds like a terrible perpetual contract that will follow you well beyond your death. 

4. Space-based method

This technique is a bit friendlier, and it has to do with space! Basically, it is the deployment of objects quite far in space that can block or reflect sunlight away from the planet – it’s a sunshade for the planet. 

Without going through the detailed calculation, in short, in order to reduce the sunlight we receive at Earth’s surface by 2%, “we’d have to stop approximately 2% of the sunlight headed towards Earth at or near the L1 Lagrange point”. 

Scientists have come up with 2 ideas to accomplish this: 

  • placing an enormous constellation of 16 trillion small mirrors at L1 Lagrange point to deviate the sunlight on its course to Earth
  • placing a (series of) large space lenses in orbit at L1, refracting sunlight away from Earth. 
space lens
This illustration, with wildly incorrect distance scales, shows the principle of a space lens. The basic function of a space lens is to mitigate global warming, refracting sunlight away from the Earth. The actual lens needed would be smaller and thinner than what’s shown here, and could be accomplished with a large array of small lenses instead of one enormous one (Source)

The only thing scientists haven’t solved is that 1) this sunshade technique is extremely costly at the moment (several trillions of dollars) and 2) the solution is temporary and will need constant maintenance, as “without any intervention, they will drift away and out of their ideal positions on timescales of just a few years.”

As much as I love anything space-related, if I were a policymaker, I would spend these trillion dollars on more plausible solutions on Earth. 

5. Decreasing the amount of high altitude cirrus cloud. 

Alright, what is cirrus cloud? 

It looks like this:

Cirrus clouds
Cirrus clouds – short, detached, hair-like clouds found at high altitudes. (Source)

Alright, what does cirrus cloud ever do to us so that we have to“kill” it off to cool down the planet?

It never does anything to us, but the argument goes like this: clouds, in general, both reflect sunlight (which is good for a warming planet) and absorb warming infrared radiation (which is bad for a warming planet). But cirrus clouds absorb more infrared radiation than reflecting sunlight, which results in a net warming effect. If we thin or remove them, we would reduce their heat-trapping capacity. 

And how do we thin cirrus clouds out? We inject particles into the upper troposphere to reduce the number of cirrus clouds. 

With what? Very likely with a transport device run by fossil fuels. Cheers!

Direct air capture: sucking emissions out of the air and burying them deep in the ground

You might say, “okay those previous ideas are super wild. Can we please go back to the more familiar ones please?” 

One of the most talked-about climate techs is indeed Direct air capture (DAC), and other variations such as Carbon capture and storage (CCS) or Bioenergy with carbon capture and storage (BCCS).

If we look at the bigger picture, CO2 removal is essential – it’s already built into the calculations of the IPCC. One thing we must clarify though, CO2 removal includes many different techniques, some of which have nothing to do with technologies such as the growth of organic matter (e.g. planting new trees) or the storage of removed gas permanently in different forms (e.g. preserving pristine forests, fighting against permafrost thaw, etc.). 

Yet, somehow in our public imagination, CO2 removal is the synonym for an active action of sucking emissions out of the air. 

meme elon musk tree

But no matter, let us examine Direct air capture, a process that goes like this: 

  • large fans draw in air from the atmosphere
Climeworks’ first commercial direct air capture (DAC) plant, based in Hinwil, Switzerland
Climeworks’ first commercial direct air capture (DAC) plant, based in Hinwil, Switzerland (Source)
  • filters which contain engineered chemicals concentrate CO2 from the air
  • the filter material is heated to release the captured CO2 into storage units, while filtered, CO2-free air is released back into the atmosphere. 
  • Here’s how the geological storage looks: 
geological storage from Direct air capture
One type of geological storage includes injecting carbon dioxide underground into certain types of rock. These rocks then will be buried deep into the ground and stored there forever. (Source)

According to the International Energy Agency (IEA), there are 18 direct air capture plants operating worldwide in 2022, capturing almost “0.01 Metric ton CO2/year”, and “a 1 Mt CO2/year capture plant is in advanced development in the United States.” By 2030, DAC might be scaled up to capture almost “60 Mt CO2/year”. Just a reminder: the world emits about 34 billion tonnes of CO2 per year.

In terms of cost, as seen before, the range of costs for DAC varies between $125 and $335 per tonne, depending on the technology choice, low-carbon energy source, and the scale of their deployment. For comparison, most reforestation costs less than $50/tonne


Climate tech is indeed a fast-growing industry, which surpasses $16.9 bn in 2022. Whether this is just another playground for Wall Street investors to make money, or there is a genuine techno-optimism in tackling climate change, one cannot deny 2 important points:

  • First, climate tech still bears many uncertainties in terms of potential, cost and side effects. 
  • Second, there are other existing solutions, both tech-related and non-tech, that can drastically cut off emissions. 
    As put by Elizabeth Kolbert in the book Unter the white sky, “to stay under 2°C, global emissions would have to fall nearly to zero within the next several decades. To starve off 1,5°C, they’d have to drop most of the way toward zero within a single decade. This would entail, for starters: revamping agricultural systems, transforming manufacturing, scrapping gasoline and diesel-powered vehicles, and replacing most of the world’s power plants.”. These levers that Kolbert listed are already available to us. We just lack a collective political willingness to make the transition. 
    Likewise, as discussed in the book “No Miracles Needed”, Professor Mark Z. Jacobson of Stanford University explained how today’s available technologies can already halt emissions, allowing us to switch away from using fossil fuels to using renewable sources.

Indeed, planting and preserving forests, reinventing agricultural and industrial systems, and adapting our lifestyle to a less-waste approach cannot bring as much money to investors and the economy as this blooming climate tech industry does.

So, if you were a policymaker, what would you do? 

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