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Comment by VeejayRampay | Hacker News Reader

It's nice that we're looking to alternative ways to capture and store atmospheric CO2, but at time it also does look like we're working too hard to replicate a system that does that already (and has for a long time): plants.

Or does it mean that the time of planting trees and preserving forests is over now and we have to do it another (most often less efficient) way?

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The problem with plants is that they do not sequester CO2 permanently; plants grow, die, and decompose, releasing carbon back into the atmosphere. Trees certainly work as a buffer in the sense that carbon in plants is carbon not in the atmosphere, but the amount you could hold is tiny in comparison to the amount that must be sequestered back in order to make a meaningful change in atmospheric and oceanic CO2 composition.

Nonetheless, plants have important benefits, since they alter the local climate by changing the albedo and perspirating. Perspiration of plants in jungles helps to create clouds and regulate humidity, and would help to counteract some of the negative effects of climate change.

>Trees certainly work as a buffer in the sense that carbon in plants is carbon not in the atmosphere, but the amount you could hold is tiny in comparison to the amount that must be sequestered

Is it? Let's do the math.

Absorbing the 350 teratonnes of human emitted carbon[1] over the 8.4 billion hectares of Earth's non-tundra / non-desert land surface area[2] works out to... 42 tonnes per hectare. If we can green deserts[3] that drops to 30 tonnes.

That's 30-40 trees per hectare, at 1 tonne per tree.[4] Or 3 kg per square meter of soil carbon, the equivalent of 25-35 cm of topsoil. More likely some combination of the two. Soil carbon is stored up to 40 meters down by deep rooted plants.[5]

Most of our land management is via agriculture, so agriculture seems to be the only lever long enough to make a dent. Practically this implies transitioning from soil destroying tillage to soil building cover crops, long-distance imported fertilizer to in-situ fertility produced by soil organisms, and ecologically unstable monocultures to resiliant polyculture, agroforestry, and rotational grazing systems.

The "gotcha" question is not whether we can replace our existing agriculture with these systems. The question is whether we can replace our existing agriculture with itself. Any unsustainable system is, by definition, not a viable replacement for itself.

[1] http://petrolog.typepad.com/climate_change/2010/01/cumulativ....

[2] http://cnx.org/contents/TWFXbERo@1/The-main-biomes

[3] https://www.youtube.com/watch?v=2xcZS7arcgk

[4] http://cabiblog.typepad.com/hand_picked/2011/06/ever-wondere....

[5] http://www.soilquality.org.au/factsheets/organic-carbon

Note that big farmers have already replaced "soil destroying tillage" with "soil building cover crops". Farm news is full of stories about early adopters 10 years ago bragging about how they are now building soil organic matter with a corresponding reduced need for fertilizer. The big farmers recognize the impact this has on the bottom line. Your mid sized farmers see that extra $10/acre in fertilizer as a cost of business and don't realize they could reduce it.

Unfortunately "long-distance imported fertilizer to in-situ fertility produced by soil organisms" cannot work if food is exported off of the farm. Every gram of food taken off the farm includes some micro-nutrients - various minerals that are required for life that have been removed from the soil and taken elsewhere.

Agreed, we're making a lot of progress on this front!

>Unfortunately "long-distance imported fertilizer to in-situ fertility produced by soil organisms" cannot work if food is exported off of the farm.

It's not like there's a shortage of rocks (where soil bacteria and deep rooted plants harvest and dissolve micronutrients) or air (the source of carbon, as well as nitrogen fixed by rhizobium bacteria in root nodules). Soil tests only look at dissolved nutrients, not those yet to be released from the minerals in rock, which range in size from bedrock to clay. This is detailed in the video I linked.

But it certainly helps if you recycle human waste into fertilizer, rather than just releasing those nutrients into waterways (and ultimately, the ocean) or landfills. The key is to close the fertility loop while also interrupting the fecal-oral route. Thermophilic composting or biogas digesters can do this on a small scale, and systems like those used by Milorganite can do this on a city scale.

Isn't soil basically just decomposed organic matter, i.e. a big carbon store? What fraction of a plant's carbon goes into the soil vs. into the air?

In most soils the carbon is eventually released by the decay process (through decompositor organisms), though some generally stays sequestered (witness terra preta for instance). Some soils like peats and taiga are strong sinks as they prevent complete decay of organic material, and thus release of the carbon (until they're burned away).

By burying a plant, you could consciously make that fraction very close to 1. This is a way to fertilize the soil for future plants, and is called hugelkultur.

Hugelkulture doesn't involve burying the plants very deeply though - I suspect that it's shallow enough that CO2 that's released during decomposition can easily make it back to the surface.

Most the CO2 from fossil fuels comes from ancient bogs, where plants were prevented from decomposing for long enough that they could eventually turn into materials like coal and petroleum. In essence, they were a result of taking plant matter _out_ of the biosphere, which is sort of the opposite of hugelkultur's goal.

Hugelkultur is intended primarily to act as a long-term (5-20 year) fertilization and water absorption mechanism, so that other plants planted on top of the mound grow better.

In that context, you will have a net-positive CO2 absorption (or, a net-negative CO2 release into the atmosphere).

Biochar is a possible method to permanently store the CO2 captured from plant matter.

Playing devil's advocate here, water vapor is an incredibly powerful greenhouse gas, even more so than CO2.

I was hoping that someone would mention biochar. Heating your house using the leftover heat from the process of creating biochar could be carbon negative.

I agree there's potential in its use, but what I'm afraid of is 1) the high nutrient requirements needed to grow the biochar at a scale useful to offset global warming, and 2) Biochar is basically coal, which could be burned and converted into CO2 again.

>the high nutrient requirements needed to grow the biochar

We seem to have forgotten that natural forests are incredibly productive, and don't need artificial fertilizer. So we have a proof-of-concept. How do they do it, and how can we emulate those processes?

Spoiler alert: soil (along with the root action of plants) is essentially a flat biological nanomachine that breaks down solid rock and fixes nitrogen, manufacturing fertilizer in-situ. https://www.youtube.com/watch?v=x2H60ritjag

Of course the logical way to do this is not to create some vast new land use category ("carbon forests" or similar), but to transition our largest current land use category -- agriculture -- from a carbon-releasing to a carbon-sequestering mode. It also helps to increase biomass per hectare in suburbs, by transitioning our current low-carbon-density lawns over to a biome that buffers substantial amounts of carbon.

This is the fundamental insight behind Permaculture btw, which has been working on figuring out exactly what this looks like. It's a hard problem yes, but one with existential importance for humanity.

>Biochar is basically coal, which could be burned and converted into CO2 again.

...so don't do that. :) It's it obvious that burning coal also needs to stop for effective climate mitigation?

In this application, density matters. Biochar is extremely low density, and high in surface area, which makes it an ideal soil amendment which buffers rainwater and provides microbial habitat (not to mention raw carbon for building into soil biomass). By contrast actual coal is nearly worthless in this application.

Bury it back. We seem to have huge cavities from used-up coal mines. We could refill them.

I have a new answer for the Fermi paradox. Any sufficiently advanced civilization will develop an extreme "leave no trace" view for ecological reasons.

They refill coal mines, plant trees where there were once cities, and silence radio emissions so that everything appears to be in its "natural" state.

"Any sufficiently advanced civilization is indistinguishable from nature."

Love it!

Yes plants die. But don't they also multiply automatically? Doesn't that address the issue?

Sure, but space is the limited resource over which they compete. Smaller plants that can't draw enough resources die or succumb to pests. It's much like animals that have a large number of offspring given their high mortality rate.

Wood can be preserved for centuries, and be very useful as a construction material during that time.

Or you can sink it in the Baltic, where nothing consumes it.

We pull almost all of the CO2 we burn from coal and oil, which were basically underground carbon reserves. To replace all of that CO2 with plant matter would take an immense amount of nutrients, which have to come from somewhere. Then there's the chance that the plant matter will turn to coal or oil again, meaning it may be used again. By turning the CO2 directly into carbonate, you both remove the need for nutrients and turn the CO2 into a form that is both incredibly stable and not useful for any energy purposes, lessening the chance that it will make its way back into the atmosphere.

Plant nutrients are minerals, primarily nitrogen, potassium and phosphorus, in the base form of inorganic compounds or salts. When a plant dies it decomposes and the minerals are released and "recycled". Certainly that's how fossil carbon got to be stored in the first place (by growth of plants) so obviously the availability of nutrients in soils was naturally adequate to support the deposition of carbon.

Carbonates are among the most common minerals on earth, particularly as calcium carbonate in its many forms. Calcium carbonate is slightly soluble in water and subject to degradation in acidic environments. While hardly an impervious carbon dioxide store, that's a benefit in that its easy degradation makes it an extremely useful mineral supporting essential infrastructure industries.

IOW sequestering carbon as carbonates doesn't imply the CO2 is inaccessible but simply not reduced to an elemental or hydrocarbon form readily usable as an energy source. It's a trade-off between storage in an easier/quicker non-energy form or a protracted/difficult-to-implement energy-source form. Worth considering that in geological time the carbonate vs. carbon storage pools will probably "even out" since both are clearly mutable.

Exactly. We have pulled an unnatural amount of "usable carbon" to the surface, which, even if it becomes a part of a natural, stable, cycle, will leave us with a higher net amount of CO2 in the atmosphere. We can only go back to "natural" CO2 levels through unnatural means, unless we are willing to measure time on a geological time scale (the millions of years it will take to replace oil reserves from the swamps of today). So until then, we would still be dealing with an acidic ocean and a greenhouse atmosphere.

>We can only go back to "natural" CO2 levels through unnatural means

Ok, but let's be careful not to exclude the middle here. "We got here by mining (an industrial activity), therefore we can't use plants in any part of a carbon sequestration chain (even one that also involves industrial activity)." Trying to use this argument as a blanket ban on plants becomes little more than an appeal to sympathetic magic.

The only thing that matters is how much CO2 a technique can buffer (annual production x time constant), not whether or not it uses plants at any stage. Plants already have enormous annual production, but for economic/thermodynamic reasons it's hard for purely factory-based techniques to achieve sufficient scale. It becomes a money sink both up-front and operationally, respectively because A) factories are expensive, and B) hard thermodynamic constraints mean that it's at a fundamental competitive disadvantage compared to any typical [reminder: energy consuming] factory.

> therefore we can't use plants in any part of a carbon sequestration chain (even one that also involves industrial activity)

Not sure where your logic is coming from here. I am not saying we shouldn't use plants, but I am saying that even if we let forests retake "all the land," the stable CO2 level would be a bit higher than pre-industrialization, and it would stay that way for a long time until dead plant matter returned significant amounts of carbon to the deeper parts of the crust.

Therefore, using other methods like the one in the article are necessary if we want to reduce CO2 levels.

>let forests retake "all the land,"

I agree, a hands-off approach is insufficient. We would need to actively manage those forests (which is just as unnatural an activity btw), using intelligent design to improve upon the carbon density possible solely from blind natural processes.

Big industrial thermodynamic sinks don't scale (and imo never will), simply because they can't economically compete with conventional energy consuming factories. An approach is needed that sequesters carbon while also producing sufficiently valuable goods to society (ie probably not rocks). Food is one possibility, and can avoid carbon futility since in perennial systems the annual food yield is a small percentage of the total carbon stored in the biome.

I've been doing preliminary research on what kind of high-density trees grow reasonably fast in different climates. If the wood has a high enough density it will sink in water without treatment. Wood that has been submerged can take 100s of years to decay. Hence it might be possible to lock away a lot of carbon and give us some breathing room, by repeatedly clear-cutting and reseeding forests and sinking the logs. Even without high-density wood, it might be worth the effort to treat the timber so that it will stay sunken. I did some estimates previously that suggest the amount of land area that would have to be dedicated to this to reduce atmospheric CO2 is not unreasonable.

Why sink when you could dehydrate it in the desert? Rot needs water.

Part of the equation is do what makes the most sense locally. So sure, if you are closer to desert, that's the way to go.

If you are close to the desert you probably don't have forests though. Tree need a lot of water, as things get dryer the land transitions to grassland before desert.

Of course mountains are often a factor. There are deserts at the base of forested mountains. The mountain takes all the rain.

Wonder what that would do to the desert over time. If it could reclaim some desert land it would be wonderful.

Plants don't usually store CO2 long term. You have to do something with them after they grow, or else they decompose and put the CO2 right back into the air.

> Plants don't usually store CO2 long term.

That's not true, a stable mature forest is a long-term carbon store, the release from decomposition being offset by capture by new growth.

And depending on the underlying soils it may be a net sink until it's clear cut and burned away (e.g. peat swamps as in south-east asian islands).

The point is that a stable forest neither absorbs nor emits net carbon, so if we want to reduce/reverse the rate at which carbon in the atmosphere is growing we need an ongoing net carbon sink. Solid C02 storage can potentially provide this.

> The point is that a stable fotest neither absorbs nor emits net carbon so if we want to reduce/reverse the rate at which carbon in the atmosphere is growing we need an ongoing net carbon sink. Solid C02 storage can potentially provide this.

Growing forests are carbon sinks, until the forest stops growing (and it becomes a carbon store)...

Yes of course, but unlike solid storage, there isn't nearly enough feasible areas to grow forest for a long-term solution.

I would (non sarcastically) like to see the numbers behind that.

Human carbon emissions are currently about 10 billion tons annually (10 Gt/yr), which equates to about 40 Gt/yr of C02.

http://www.wri.org/blog/2013/11/carbon-dioxide-emissions-fos...

Total carbon stored worldwide in biomass, dead wood, and soil is about 640 Gt.

ftp://ftp.fao.org/docrep/fao/010/i0105e/i0105e04.pdf

Of the 550 Gt of carbon humans induced into the atmosphere since 1870, 390 Gt was emitted directly (through burning, cement production, etc), and only 160 Gt was through deforestation and other land use change.

I think the statement you replied to was referring to each individual plant: the forest can capture carbon for thousands of years potentially, but each tree captures carbon for not much more than its lifetime.

> I think the statement you replied to was referring to each individual plant

That's a nonsensical argument and quite literally missing the forest for the tree.

Peat is a great long-term storage for atmospheric carbon [1].

[1] http://www.ipcc.ie/a-to-z-peatlands/peatland-action-plan/cli...

You mean like eat them?

No, eating a plant turns it into CO2. Our / animals' bodies burn the sugars (which were the store of C) into co2 and energy, using the original o2 produced by the plant to convert that co2 into those sugars.

It's more meaningful to reason about co2 storage in terms of area dedicated to plants, than the plants themselves.

Cutting them will indirectly release the carbon. Making plants into building materials or cabinetry keeps the carbon locked.

Though even cutting it to firewood has zero sum long-term CO2 balance as long as the forest itself sustains.

s/cutting/eating/ ?

Reforestation is good in regions that used to have forests. But using rocks might also work in ardi regions where freshwater is a limited resource (I assume they can just use salt water to pump CO2 into the rocks).

And you can't just plant forests everywhere, for example china experiences issues with its Green Wall, where the trees soak up so much water that it causes the ground water level to fall.

Its not either or at this point, you need both (as many as possible) solutions. In some regard CO2 storage solutions are better because you can make use of lower priced real estate like ocean floor vs growing plants and forests which take away real estate that can be used for human habitation and agriculture. Also CO2 storage is more stable in time. Like 100 years from now, people might just choose to cut down the forests and just release all that stored carbon back.

For $15/US resident/year (on average), you could sequester all the carbon you produce that year by having 150 trees planted in return for your donation: http://shindyapin.tumblr.com/post/141034501197/climate-chang...

Please do research into whatever organization you choose to use.

Some of the carbon offset organizations that plant trees are having a hard time finding people and land to do the work, since cash crop trees tend not to be good carbon collector/stores, poor farmers tend to forego the pay-for-trees to be able to grow cash crops.

I don't know the specific organizations, but I have heard that this can be a complication issue.

Donating to smaller charities tends to go to more specific projects, like these:

https://www.cooleffect.org

https://www.coolearth.org

https://carbonfund.org/projects/

http://www.edenprojects.org

It'd be great if any of these had published progress reports (not to say they don't but I haven't read them). Seems like you could fake one of these pretty easily if you tried.

REVISION: If true, seems like it would feasible for the US, but unclear how regions like Africa & Asian would do the same. Any ideas?

Below is the original comment with correction for accounting error.

_________

$15 per person per US person[2] per year does not sound like a lot, but in sum per year it's a massive amount of money; amount would be $4,847,228,805.

For example, per person using the 2014 net collections[1] of the US's net tax collections divided by the population estimate for July 2016[2], the US revenue per person is $8,000.

[1] ($2,690,755,432) https://www.irs.gov/uac/soi-tax-stats-collections-and-refund...

[2] (323,148,587) http://www.census.gov/popclock/

On the spreadsheet, money amounts are in thousands of dollars.

The US tax charts are reported in thousands, so 2.6 trillion / 323 million = 8k per person, not 8

Thanks, missed the "Money amounts are in thousands of dollars" - corrected the comment above.

What do taxes have to do with it? What I'm saying in my blog post is if you want to do something about your personal CO2 emissions and you live in the US, you could donate $15/year to sequester all of them (if you don't live in the US, you would probably need to donate less than $15 to sequester all your CO2 for that year, but you would have to do the calculation yourself).

Edited my comment to reflect this accounting error, revisit the comment to see the correction and related revision.

At the point you're spending billions in sum in a country for a reoccurring & necessary theoricially non-profit service, it would make more sense to do this via the government; yes, I get it's not a requirement, assumes government is functions efficiently, etc.

It might theoretically make more sense to do it via the government, but you can do this right now without waiting for the government.

If that's all it would cost, I would gladly donate $45. $15 for myself and $30 for my parents.

This is the second year I've been donating $100 for my family of six, and a bit more on top of that. (Sorry if this comes off as bragging; my intent is to show that I am putting my money where my mouth is.)

Just realized your username, checked site for updates, and posted the most recent update here, "AutoMicroFarm: My YC Results, AutoMicroFarm Product Development, Moving Forward"

https://news.ycombinator.com/item?id=13457660

Thanks for posting an update - if the titles not right, just post a comment and I'll update it.

Thanks saycheese! I posted that blog post to HN myself a few days ago, but it did not get any traction. :)

Agree, in the context of the annual budget of the US, seems like this is possible at scale, but feels like this is too simple of an answer; looking into it.

Your first link, the numbers are in thousands of dollars so the correct amount is $2,690,755,432,000 nearly 3 trillion dollars.

Thanks, corrected the error.

It doesn't sequester the carbon for very long, though --- the carbon lifecycle of a tree is, what, decades? It consumes carbon when it grows, and then it releases it again when it rots. So it's not really a long term solution.

We burn oil to produce cheap energy and we get CO2 as a byproduct.

If you want to reverse the process you need some energy, so what would be the point of burning the oil in the first place?

If we want to reverse the CO2 we released by burning all these fossil fuels, at some point we'll need to essentially "unburn" them - and yes, that would necessarily involve "paying back" all the energy humanity got from burning these fuels.

We'd only need a large amount of energy if we want to turn it back into a high-energy compound like oil or coal. The method described in the article has CO2 turning into calcium carbonate, which does not need an energy input (in fact, it releases energy in the form of heat)

The energy could be from wind, solar -- in fact it might be an ideal use case for those sources if the process can be done intermittently, i.e. whenever the wind is blowing or the sun is shining.

Or you could envision large carbon sequestration plants powered by on-site nuclear.

> Or you could envision large carbon sequestration plants powered by on-site nuclear.

I'm not sure I understand, you're suuggesting that we

1. Burn oil to produce energy (and CO2 as a byproduct)

2. Use the energy to do X

3. Use non-fossil energy to get rid of the CO2 we created during step 1.

When we could just do:

1. Use non-fossil energy to do X

Am I missing something?

Transport.

Fossil fuels are incredibly energy-dense and convenient to transport and work with, while renewables aren't. There's plenty of transport systems that are utterly reliant on fossil fuels and couldn't be converted to renewable energy. Carbon sequestering would allow continued use of these while staying carbon-neutral.

That seems like a very circuitous and inefficient way to avoid electrifying transport. Batteries are hard, but they're not that hard (as Tesla's rapid progress is demonstrating).

Land transportation accounts for the majority of liquid fuel use, and much of that can be replaced by battery power assuming that battery costs continue to drop. I'd guess that battery powered airliners and long distance cargo ships will not become practical. Those and other transport applications particularly demanding of energy density account for a large enough residual of liquid fuel use that it's worth thinking about how to avoid fossil emissions from them. Synthetic liquid fuels made from non-fossil energy sources is one way to do it. (Biofuels are an option too, but plants are a lot less energetically efficient than solar farms, so you need a lot more production area for biofuel than synthetic fuel.)

>I'd guess that battery powered airliners and long distance cargo ships will not become practical.

We shall see. For whatever it's worth, Tesla's CEO disagrees. https://www.youtube.com/watch?v=0871VJfvD1c&t=57s

>I think all transport, with the exception of rockets, will go fully electric.

This is the most recent example, but he's been saying this since at least 2013. Surprisingly, he's also made it clear that he thinks this applies to ships and planes too. http://www.digitaltrends.com/cool-tech/elon-musk-electric-ai...

I do not think batteries will ever get a useful enough energy/weight ratio for airplanes. https://en.wikipedia.org/wiki/Energy_density Not only does jet fuel have a much better energy to weight ratio, but you don't have to carry the weight of your spent fuel. A battery powered airplane needs to get all its fuel to altitude while a fuel powered one has much less mass to get up (and stop when you get to the ground).

Ships probably will see batteries as an asset: they can place them in ideal locations for weight distribution/stability.

I think it's hard, yes. But I also think forever is a long time. ;)

You certainly can't get there by taking an existing aircraft, removing the fuel and replacing it with batteries. It's the same fallacy as the gasoline automakers make with electric cars, and it results in a worse vehicle design. The whole system has to be re-imagined from the ground up to exploit the advantages of electric propulsion.

Several of the design concepts for his proposed supersonic VTOL electric transcontinental commercial jet airplane have already been revealed:

* The plane would fly at high altitude, somewhere around 80,000 ft. Combustion airplanes have a 30-40,000 ft ceiling limited by the need to ingest oxygen. Due to the exponential decay of density with height this dramatically reduces drag, thereby reducing engine power and structural stress. Coincidentally this is also higher than almost all bad weather.

* VTOL is easier since electric motors have a better power:weight ratio than turbine engines. This eliminates constraints due to runway length and width, and means the wing can be more closely optimized for cruising. It also means smaller airports are possible, reducing gate fees.

* The wings also don't need to double as liquid fuel tanks, and don't need to handle different stresses when empty vs full.

* A high mass fraction of batteries compared to combustion aircraft (mid to high 70% range). Energy density at least 400 Wh/kg (which as you point out, is still much lower than kerosene).

* Eliminating the tail section in favor of gimbaling the electric fan, again reducing drag and weight.

* You also get about a 1% drop in weight compared to existing jets due to reduced gravity and centrifugal force.

A good video compilation of quotes is https://www.youtube.com/watch?v=erjdYiwoYAo

Batteries are still a long way from being useful for ships, long-haul trains and trucks, and large aircraft.

0. There's a lot of carbon in the air and we might want to get rid of it.

Yes, I was unclear. We've presumably got 100+ years of industrial carbon emissions to clean up if we want to get back to "pre industrial" atmospheric carbon. Plus ongoing emissions from transportation even if all electrical power is converted to renewable or nuclear.

I thought algae was far more efficient than plants?

It is, but where would you get the nutrients needed to grow the algae at a scale needed to offset global climate change?

There is research being done on iron seeding/fertilization of barren ocean waters [0]. In such places, iron is the limiting factor for algae growth.

[0] https://en.wikipedia.org/wiki/Iron_fertilization

How about (farm) waste water runoff?

This has been suggested before. Scale is still hard. I read an article in the UC Davis algae magazine (http://www.algaeindustrymagazine.com/department/education/we...) a while ago that talked about flooding a fairly large acre (hectare) parcel with water, growing a layer of algae on it, then burying the algae. (process flood, algae mat grows, drain/evaporate, and plow it all under, then repeat.) The algae decomposition process releases methane (worse than CO2).

only if we cannot capture methane. If we can capture it, we can run it through an engine and get the energy back. Most landfills are already doing this: it adds some extra profit to the bottom line.

I have no idea if this stores any carbon anymore though.

> The algae decomposition process releases methane (worse than CO2).

Under what conditions does this happen?

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