
The impact of direct air carbon capture on climate change - _Microft
http://cognitivemedium.com/dac-notes
======
jarvist
I'm not sure if this article hammers home the key point: extracting carbon
from the air always takes more energy that was gained by burning the fossil
fuel to make that carbon. This is inevitable due to the entropy cost of de-
mixing CO2 from the air, and from the limited efficiencies of thermal power
generation (~33-40% for a coal power plant, perhaps 20% in an internal
combustion engine), and limited efficiency of the carbon capture technology.

So it only makes sense to spend energy on sucking CO2 out of the atmosphere,
once you've already de-carbonised everything which you possibly can.

Maybe it has a future role (>2050? >2100?) to start using excess low-carbon
energy to take CO2 levels back to their pre-industrial level, or to constantly
offset hard-to-decarbonise technologies such as air travel.

~~~
Robotbeat
Not objectively true, as plants and even rocks grab CO2 out of the air pretty
efficiently. From a thermodynamics standpoint, you can burn fossil fuels at
50-70% efficient (50% is not uncommon), and the actual theoretical lower bound
of CO2 direct air capture is ~20 kJ/mol,[0] or about 1.7MJ/kg of elemental
carbon, compared to 33MJ/kg for burning elemental carbon (same as high grade
coal).

(Burning methane is even better as it releases much more energy per unit CO2
i.e. ~860kJ-per-mole-of-CO2 vs anthracite's ~400kJ.)

And as others have said, rocks actually are able to _exothermally_ absorb CO2
permanently. It's possible to speed this up by grinding rocks to a powder,
placing in water with a catalyst.

...none of this is to say I support relying on direct air capture and just go
ahead and burn fossil fuels. We need to keep that in the ground and transfer
the whole civilization to non-fossil fuels, otherwise if some populist jerks
wer elected, they could just order the expensive direct air capture program to
stop (can't do that if you're already transitioned to clean energy and all
your wellheads and drills and coal mining equipment are rusted or melted down
for scrap).

Source: [0]
[https://www.researchgate.net/publication/257177020_The_therm...](https://www.researchgate.net/publication/257177020_The_thermodynamics_of_direct_air_capture_of_carbon_dioxide)

~~~
xbmcuser
With solar prices hitting negative rates for some periods in a day capturing
carbon and converting into burnable fuel will probably start making sense in
the next few years.

~~~
svara
As long as there's still fossil fuel powered transportation, it would make
more sense to use that excess power to charge batteries, since that converts
electricity into motion more efficiently than taking the detour through
synthetic burnable fuel.

~~~
xbmcuser
Destroying fossil fuel powered transportation then replacing them with
electric would actually produce more carbon. All new transportation should be
electric but the already running transportation if can be run on captured
carbon would result net carbon decrease.

------
spodek
Not a word about the most effective, cheapest strategy: reduce emissions?

Most Americans could reduce their emissions by 75% while _improving_ their
standard of living by buying less junk, wearing a sweater in the winter,
eating more healthy, and other low hanging fruit that will make them more
active, healthy, connected to their communities, etc.

Reduce consumption by half. There, I just saved us $300 million.

How is reduction not our top priority and activity??

~~~
shartshooter
Because it’s also the least effective strategy. The reality is getting
_nearly_ everyone to change their behavior just isn’t gonna happen.

Even if everyone in America went vegan, showered once a day and biked
everywhere wouldn’t change much with impoverished countries coming out of the
third world. If you can’t get them to change then it doesn’t really matter.

Big problems require big, comprehensive solutions. For that you need
government to function effectively regulate, make climate bills countries can
stick to.

We already have the tools we need to get climate change turned around but we
don’t have the _political_ will.

~~~
seminatl
Wait. Does the average American shower more than once daily? Is water
consumption/heating for showering even a measurable component of GHG
emissions?

------
btilly
I would have liked to see
[https://projectvesta.org/](https://projectvesta.org/) commented on in the
article.

They claim to be able to sequester carbon by scattering olivine rock in an
active and warm coast. The cost of the rock is $25/ton now, with the prospect
of $10/ton in the future. Plus whatever it costs to break it up and scatter
it.

That makes it at an interesting price point if it works as advertised.

Even more interesting to me is that the absorption happens in the water.
Meaning that it can counteract ocean acidification near the coral reefs that
are the most vulnerable.

~~~
tekstar
I believe this type of project is referred to as geo-engineering, which is a
bit more controversial as it's typically assumed that the side effects are
somewhat unknown.

~~~
yifanl
They're targeting a pilot within the next 5 years on a single beach, which
should help towards figuring what side effects exist.

They also note there exist naturally occurring green sand beaches
([https://en.m.wikipedia.org/wiki/Papakolea_Beach](https://en.m.wikipedia.org/wiki/Papakolea_Beach)),
though those are tourist spots and probably haven't been deeply studied.

------
dv_dt
If you're going to continue to burn fossil fuels, it seems better to burn it
in a plant that inherently captures the carbon then trying to wrangle it back
after it's release. The interesting part of the Allam cycle for power
generation is that supercritical co2 is the working fluid for the turbine, and
when you burn the fuel it increases the mass in the closed circuit. Both the
size and the efficiency of the plant also purportedly improve with the Allam
cycle too.

[https://en.wikipedia.org/wiki/Allam_power_cycle](https://en.wikipedia.org/wiki/Allam_power_cycle)

[https://www.netpower.com/technology/](https://www.netpower.com/technology/)

~~~
pfdietz
That would be true, if the power plant has high capacity factor, and if it
stationary, and if it is located near a place where the CO2 can be
sequestered.

But if you (say) have peaking turbines that are intended to take over when
renewables or short term storage are not available, they may have very low
capacity factor. It could be economical to have them release the CO2 into the
atmosphere, then steadily scrub that CO2 back out again, especially if that
scrubbing could be done in a location with extremely cheap solar energy (like,
say, Chile).

~~~
dv_dt
I'm for pursuing both options really. There are likely solution areas where
both would be a win. And we really know not enough about the end direct cost
of either until sufficient numbers are built out - and we should build out
both to at least 10x what the prototypes do. The real problems are
governmental policy, and then financial policy to get the attention and
scaling going on any of these solutions.

------
whytaka
Michael Nielsen, the author, also wrote a multi-part intro to neural networks
([http://neuralnetworksanddeeplearning.com](http://neuralnetworksanddeeplearning.com))
which really cleared up for me the inner-workings and mathematics of machine
learning quickly but without skimping on details.

I'm very excited to read what he has to say here.

------
40four
I've been interested in these types of technologies lateley.

> _that many people are extremely pessimistic about climate change. They can’t
> imagine any solution – often, they become mesmerized by what appears to be
> an insoluble collective action problem – and fall into fatalistic despair._

More and more, I find this description matches my thoughts on climate change.
I'm really beginning to think the problem might require building carbon
capture solutions on a huge scale. We might have to engineer our way out,
because it doesn't appear we are slowing down emissions fast enough.

~~~
DanTheManPR
We are geoengineering already, so we are going to have to deliberately
geoengineer our way out of the problem.

~~~
40four
>we are going to have to deliberately geoengineer our way out of the problem

Agreed, I'm really starting to think this will be the only way.

------
jacknews
Fast-growing trees, which are then burnt to charcoal (and some energy), which
is then put in the soil as biochar. Could be very cheap/low-tech and at the
same time improve soils.

~~~
ph0rque
Or, buried wholesale as part of a Hügelkultur.

~~~
jacknews
yes this could be even cheaper, though I'm not sure if perhaps the co2 is
released quicker as the trees decompose- charcoal can keep the carbon locked
up for centuries.

Either way, these methods greatly improve the land-use efficiency of growing
trees for carbon capture/storage, as it is stored in the soil over many years,
not only in the living trees. "putting coal back in the ground" as it were.

------
WalterBright
Just plant trees. They're cheap, solar powered, and convert CO2 to building
materials.

~~~
adrianN
Start by protecting existing forests. We're still losing rainforests ever more
rapidly.

~~~
WalterBright
Planting more trees will reduce pressure to cut down existing forests.

~~~
adrianN
In the case of rain forests, they're usually not cleared for the wood, but to
open up farmland.

------
leemck
OK to shout Eureka when you figure this out:

I have a website where I explore the idea of "not emitting fossil fuel CO2."
www.lowco2america.com

Instead of thinking in terms of "cost of extracting CO2" I have sort of
stumbled on the idea of "recapitalizing America around social systems that do
not emit CO2."

My scheme has a payment of $394 per metric ton of CO2 not emitted. The payment
from govt. funds is a prompt no bank account required electronic transfer
payment. What it can purchase is a continuing free share of the electricity
generated by the workplace parking lot, or an electric car, where the car is
free is provided the driver carries 2 or 3 workplace commute riders. The car
runs with an average load of 1 driver and 2 or 3 riders. The payment can pay
for other things or be redeemed for cash, optionally.

The ancient Chinese Tao Te Ching poem Verse 80 describes a happy society that
might sound a little bit like an America that figures out how to live well
with 2 mt per person CO2 emissions, maybe in 40 years?

------
cagenut
I really like the way the author tries to ballpark orders of magnitude and
compare against known-budgetary-things for frames of reference. That said,
talk of 10/tonne is pure fantasy, the real band is between 100 and 1000, so
the analysis here is a full decimal place naive (of course, IMHO).

Just to contribute, another americanized version of the numbers: $100/tonne of
a carbon tax works out to about $0.87 per gallon of gasoline. So if you assume
carbon engineerings pilot plant estimates turn out to be right but on the
high-end, at $232/tonne that's an almost perfect $2/gallon.

Which raises an interesting point to ponder... if anyone were capable of
extracting carbon from the atmosphere at under $200/tonne... then all the oil
companies would almost instantly switch to only building those plants. Why
fight for drilling rights and production share agreement terms when air is
everywhere.

------
leemck
To rephrase this article: The impact of direct air carbon capture will require
enormous input of energy or enormous tonnage of materials such as limestone.

Another approach to reducing the human contribution to atmospheric carbon
dioxide is to have each person adopt a low CO2 emission life style.

Just like a massive carbon capture technology, enabling individuals to adopt a
low CO2 emission lifestyle is not a free proposition. How much to pay an
individual to implement a specific low CO2 life style? Gasoline (the high
emission variety 19.6 lb per gallon) at $3.50 a gallon produces a metric ton
of CO2 for $393.

More detail at:[https://www.lowco2america.com/2018/10/gasoline-co2-in-air-
wh...](https://www.lowco2america.com/2018/10/gasoline-co2-in-air-what-are-
some-of.html)

------
bamboozled
It's really nice to even see this discussed, I've been really interested in
this topic.

It's true, at some stage we're going to have to reduce the carbon we've
already injected into the atmosphere, so why not get started now. It's amazing
how little funding this has received.

I'd actually be interested in paying for this like any other utility, as
electricity prices get cheaper from renewable energy, I'd be happy to pay a
carbon capture bill to survive and breathe cleaner air. I'd also hope this
would be a temporary thing as we completely transfer away from fossil fuels.

Pay to clean up some of my own mess,makes sense.

------
gersh
I'd like to know the land use requirements of direct air capture technology.
Will it use enormous amounts of land? What is currently on that land? Will
this entail scalability issues?

~~~
DennisP
An estimate I've seen repeatedly is that they'll take about 1/1000 as much
land area as the same carbon capture with trees.

------
itcrowd
Very well written and balanced article. Thanks for sharing these insights.
Looking forward to another "tiny corner" of your explorations of these
technologies!

~~~
_Microft
It's not mine but if you're interested in more of the author, follow
@michael_nielsen on Twitter.

------
KludgyPerl
Agriculture can do DAC:

[https://terraton.indigoag.com/](https://terraton.indigoag.com/)

------
SomewhatLikely
Don't vehicles emit other greenhouse gases too? Or would the carbon cover the
overwhelming majority of effect?

------
ph0rque
You can do it to the tune of $15/person/year:
[https://automicrofarm.com/blog/2019/03/solving-climate-
chang...](https://automicrofarm.com/blog/2019/03/solving-climate-change-with-
trees.html)

------
ForHackernews
Does direct air carbon capture at scale even exist? Is there plausible reason
to think it will exist in the next few decades?

The whole article seems like "If nuclear fusion cost $100 per MWHr, but if it
only cost $10/MWHr..."

------
hypertexthero
We need to stop callin it “climate change” and start calling it ”climate
crisis”.

------
tathougies
Good analysis, but fails to take into account the storage costs of whatever
CO2 is sequestered (or the potential to offset those costs by selling the CO2
to whatever industry uses them).

~~~
mmanfrin
> storage costs of whatever CO2 is sequestered

CO2 is not spent uranium.

~~~
pjc50
No, but you do have to keep it somewhere where it won't leak back into the
atmosphere again any time soon. Which means deep underground.

------
iron0013
You know, I'm not sure I really need to hear from any more non-experts
thinking out loud anymore. We've had enough of that. I want to hear from
experts giving their carefully considered views.

------
dwoozle
If carbon capture is good then why do they encourage composting? Shouldn’t we
be taking that organic material and burying it somewhere?

~~~
baq
we should, preferably in shut down coal mines where the carbon came from, but
that takes time, money and fuel.

------
acollins1331
Carbon capture is the dumbest and most expensive way to move forward. It would
be cheaper to just turn every coal plant into a solar farm then it would be to
capture the carbon out of the air so why even bother. Oh yeah, corporate
interests.

~~~
sinuhe69
True. Especially if nature already has the best direct carbon capture
technology since hundreds millions of years for free: trees!

~~~
ncmncm
Plants convert at most 2% of incident light into chemical energy, and spend
only a fraction of that binding carbon.

Trees are cheap but need a lot of space and water. People are cutting down
forests because they want to use the space for something else.

Ocean surface algae also collect solar power and carbon, and there is little
demand for ocean surface for other uses. Algae are limited by available trace
minerals -- cheap ones.

~~~
acollins1331
Iron seeding of the oceans to increase producer activity is currently being
done but on large enough scales to sequester enough CO2 to make a difference
it's basically impossible.

~~~
ncmncm
Where is it being done, and by whom?

The only one ongoing I know of is Sahara dust being (naturally) blown out to
the Atlantic ocean. Otherwise, just talk. Somebody who did an experiment had
his results suppressed, crudely, with a false narrative promoted in its place.
Why that was seen as necessary, and how it happened, seem even more
interesting than the experiment.

------
leh_chmp
This argument is so naïve that I had to create an HN account (downvote ready
comment for dissing HN commenters). Do note that I am not dissing the author.
He did claim a lack of expertise, but I am sad to see the comments trying to
analyze the directly presented facts than being detail driven. E.g. I saw some
reference to Allum's process of reusing CO2. What it skips is the fact that it
barely effects efficiency, but certainly sees that is better than excusing. I
still don't understand how $ among is used to measure environmental impact is
a relationship people can think is easy measure. Maybe because short term
thinking is rewarded better, hence the success of capitalism (I'm not
pro/anti, but that's the root of the philosophy). I am assuming that people
understand that Carbon capture doesn't resolve environmental changes. It
simply offsets a part of it - the global warming aspect. A LOT of impact is
straight up coming from pollution/contamination of water and soil, recurring
costs of restructuring landscapes, causing earthquakes to floods and
terraforming from receding coastlines, destruction of habitats, leading from
contaminated species to complete destruction is food sources. The cascading
effect of environmental damages is like paying a loan. As humans we are known
to be overconfident of "I can fix it". But remind me historically when THAT
had worked? Almost in all cases, it had been "I can forget this". Except in
this case, I think if we had to expend that sort of money to "solve the
problem", then we might as well just find a new planet to squander. In 50
years, we would have spent trillions of dollars unanimously and probably got
to Mars

[Edit] typos

------
basicplus2
Would love to know how many Trees/Algea farms/plants generally would need to
do the job

Also growing plants and converting to fuel is exceedingly cheap for diesel

And before anyone gets worried about food prices going up.. it takes a
surprisingly small amount of land mass to cover currect sneeds in energy,
sorry no references no time..

------
scarygliders
Here goes for further downvotes...

The entire edifice of this "human caused climate change" _hypothesis_ rests on
the premise that carbon dioxide is /the/ control knob for this planet's
temperature.

There is zero proof that this is true. Zero. So if I were you, I'd be very,
very cautious before going ahead with capturing CO2, by any method.

It's way too early for this sort of thing. Vastly more research is required
before taking a potentially disastrous decision to try to reduce the amount of
CO2 - a gas which Earthly vegetation /needs/ in order to survive!

~~~
shawnb576
Ugh, I shouldn't feed trolls...

1) AGM has hit the gold-standard of proof, it's not an open question at this
point, and CO2 is the primary driver along with other GHG [1]

2) What exactly are the "potentially disastrous" consequences of going back to
300ppm, roughly where we were for 10k years?

[1][https://www.reuters.com/article/us-climatechange-
temperature...](https://www.reuters.com/article/us-climatechange-
temperatures/evidence-for-man-made-global-warming-hits-gold-standard-
scientists-idUSKCN1QE1ZU)

~~~
scarygliders
Being called a troll for questioning a false premise amuses me no end.

Have you ever read any of the other side's information, or do you solely read
Reuters and other "CO2 is the demon!" mainstream media sources?

~~~
ratboy666
Thanks for your comments. A bit of fresh air. Really, I don't think that
demonizing CO2 is the objective. Demonizing oil and other petrochemicals seems
more likely. I think we are in a CO2 drought -- we know the planet (including
corals) had an explosion of life at the 700+ ppm CO2 level.

