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My favourite solution to this is to use some of the pyrolysis products as fuel - if you burn and release 20% of the carbon captured by the plants to power the process of burying the remaining 80% the process is still carbon negative overall, and you have a nice to use hydrocarbon fuel that can more-or-less slot into existing machinery.

The biggest problem is the scale of it - to make a significant dent in global co2 you need to be pyrolysing a lot of wood - getting towards entire-earth scale managed forests.

I also think that compared to some pie or at times mirror in the sky terra engineering projects "plants for the rescue" look more realistic at this point.

>The biggest problem is the scale of it - to make a significant dent in global co2 you need to be pyrolysing a lot of wood

The giant scale and use of land is one thing. But increasingly in many places the limiting factor be it for agriculture or forest or biomass plantations is water. While forests and vegetation have more than just a sponge effect, we should keep in mind that a scorched dry forest or a field burns easily. One may look at it as +/- net zero (what burns was absorbed by the plants we planted), it may be safer to go for high biomass yielding plants we can cut preferably more than 1x a year. In the case of fire only the carbon absorbed in the last say half a year would be released. And nasty plants such as Arundo can re-sprout after the fire. Or in a case of a prolonged drought given the right equipment one can just cut it down and get rid of the danger.

*Edit*: cut one "While" too many

Stupid idea of mine: can we start burying our paper rather than recyling it? It means every sheet of paper requires cutting down more trees, and hence putting more trees (indirectly) into the ground. If you then re-plant those trees you capture more carbon.

I presume the paper doesn't add enough to create soil and just rots.

This is actually the logic for just burying plastic: it doesn't degrade on any important timescale. Acts as a carbon sink, and keeps it out of everything. Winning all around.

Not if you got the plastic using fossil fuels and extra energy. Which is the case for most of the non-degradable plastic. Add to it that we are nowhere close to replace various types of plastics with materials obtained from non-fossil fuels.

Obtained from cellulose https://en.wikipedia.org/wiki/Cellulose_acetate does decompose fairly quickly in the soil.

But paper is pretty effectively recycled and trees aren't the only input - transport, water, and heat at the plant.

>But paper is pretty effectively recycled and trees aren't the only input - transport, water, and heat at the plant. Exactly. Moreover 1ha of Arundo produces 20-50t or more dry mass per year packed in 100mx100m area. Granted, not harvested at 0% humidity, less dense than paper. Collecting 50t of recycled paper from the containers in the city probably needs more energy for transport.

There isn't enough arable land and fresh water to meaningfully address climate change in the time necessary. Algae farming with sea water might be a good alternative if we could address disposing the the algae without emissions.

This is the critical flaw in betting mostly on trees to remove CO2 from the atmosphere.

To get to the now-unlikely target of +1.5°C by 2100, the need is on the order of 6 billion tons of CO2 to remove each year by 2050[1]. A mature tree can capture only around 22 kg a year[2], so removing 6 billion tons would require planting 270 billion trees each year. To get a sense of the magnitude of the effort, there are an estimated 3 trillion trees on Earth today; we'd need to plant just as many in only 11 years.

[1] https://www.mckinsey.com/capabilities/sustainability/our-ins...

[2] https://www.eea.europa.eu/articles/forests-health-and-climat...

270B trees @22kg/year, right?

You cut them down each year and replant, or assume that there are no trees locking up 22kg CO2/year for more than 1 year?

Better yet: you burn the plants for energy, then sequester the conveniently high concentration CO2 from the smokestack and do with it whatever you'd think would be smart to do when burning fossiles.

About the Science article: my quick skim stumbled over the word "regenerate", which tells me it's not about some material suggested for permanently binding the carbon, but about a tool to get from smokestack-level CO2 concentrations to even higher levels?

> The low tech solution for scrubbing C02 from the atmosphere is to get more plants absorbing it and prevent the plant decomposition back to CO2 or even worse to methane.

Bring back moors. Moors can sink a shitload of CO2 - and there have been a lot of moors de-watered over the last centuries to gather peat and agricultural land.

The downside is you have to convince or pay off a lot of farmers who have farmed the former moors for just about the same timeframe.

Yes, moors would help. I remember that during some floods in Europe one of the ideas floating around was to construct large polders which will be flooded as needed. No clue if catching up flood waters that would be enough to turn such polders into carbon sink.

There was some documentary about a German farmer keeping his grasslands in a moor-like state by rising the water table lowered by drainage. This did work well for him in the times of the draught but in general if I remember correctly it did lower his income.

>Supposedly if we fertilize patches of the oceans the dead algae will nicely sink to the bottom not to be release CO2 for centuries.

This is not true. Russ George is and perhaps always will be a grifter.

https://en.m.wikipedia.org/wiki/Iron_fertilization

Uh, the experiment log on that page is actually moderately encouraging. The lesson, particularly from the EIFEX experiment, appears to be that it works great provided there's adequate silica for diatoms. No reference to Russ George required.

> if we fertilize patches of the oceans

Don't we do it already with wastewater streaming down from fields, pipes, rivers...?

Yes, it is called eutrophication and is a huge pollution problem. The dead algae that drops to the ocean floor get eaten by bacteria and through that depletes the oxygen, resulting in hypoxic dead ocean. No fish and no plants, which in turn kills biodiversity both in and outside the water.

Even if the goal was to store CO2 and we didn't care about anything else, the method has additional problems. With nothing living in dead zones except for algae, the methane gas produced by decomposing dead algaes has a high risk of rising to the surface.

Yes and no. Meaning: depositing fertilizer close to the shore in shallow waters causes toxic algal blooms and suffocates everything. One needs deep, cold waters so the sinking organic matter is not decomposing rapidly.

And yes, if the winds blow the Saharan dust over large oceanic surfaces algae do grow in otherwise "desert" waters and some of the generated biomass does sink deep.

One aspect these iron fertilization experiments have ignored is albedo. Leaving any sequestration on the table, and just focussing on keeping the albedo of equatorial oceans low for as long as possible has the real potential to avoid absorbing massive amounts of solar heat into the system. That doesn't solve the co2 problem, but because you can negate the feedback loop aspect of the problem, and perhaps even make natural sequestration occur faster if you lower temperature enough. One thing I haven't been able to figure out from the data from the experiments, is how long these blooms last. The tonnage of fertilizer and the size of the bloom, yes. Also, the experiments were done in eddies mostly to isolate the effects. So an open equatorial ocean experiment would be needed. Along with better local temperature monitoring. Some satellite imagery to verify albedo would be a plus. As far as ballpark numbers, if the bloom stays equatorial, you would need about 1.5e9 USD per however long a bloom lasts in order to maintain an albedo that would initiate snowball. That is scaling linearly up from the area affected by previous experiments vs their costs.

From German Wikipedia the albedo of water changes a lot with the angle. Oceans already are "dark" when hit by sunlight at +45degs angles. So it may not be that important.

The "ocean fertilization" referred to here is not with nutrients, but with iron [0]. Apparently there are glacial runoffs at Greenland which would just need to be transported to other areas of the ocean in order to capture massive amounts of CO2.

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