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verytrivial | 2 months ago

Indeed. I've always had trouble picturing how to efficiently "unmix the cake" too. CO2 is rare and throughout the whole atmospheric column. What kind of concentration gradient can you get going to meaningfully pull it out from everywhere in human timescales? (Sorry if this nerd-snipes someone stronger with calculus than me.)

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primdahl|2 months ago

Plants capture CO2 from photo synthesis at huge scale. That seems like a great way to capture it at a higher concentration. We’d need to handle the organic matter before natural decomposition, but quite doable.

lazide|2 months ago

It’s even less energy efficient gathering up plant matter at this scale and permanently sequestering it, than getting it from the atmosphere. At least with the current technology required to harvest, move and process it. It’s why biomass is still a relatively niche ‘carbon offset’ technique.

It is also highly space inefficient and time consuming to grow and store (sequester).

Even if we converted all US cropland (and the US is one of the largest and most fertile countries for growing crops!) to growing trees, for example, we’d need multiple years of growth for every year of fossil carbon we currently release. And we’d all starve.

There is also generally less carbon by weight than you might imagine - even hardwood is typically more water than carbon when harvested, which is a big part of the problem.

To make it time efficient and also stable to store (not just rot and release the carbon immediately as methane or the like), it needs to be converted to a more stable form like charcoal or coke. Which further decreases efficiency and adds costs.

Near as we can tell, it is much better to just not release it (electric cars + solar?), or geo sequester it (olivine minerals seem promising!) or capture and sequester it directly (inefficient, but hey, there are techniques that should scale like pumping back into the original fossil aquifers!).

The biggest issue is economic (and hence political) - fossil fuels are energetically the equivalent of free money. It’s pretty hard to convince people to stop getting free money and pay money instead!