How are they irrelevant? The reason there are countries that developed and became first world countries is precisely because they used fossil fuels. Preventing other countries from doing the same for the sake of protecting the environment (which by the way is never in stasis) is simply condemning people to poverty, disease, basically to cripple poor nations. It seems very nationalistic under the guise of protecting the environment.

>undoing emissions from 1850-2020 would require more than the total biomass of the entire planet.

So we created more carbon than existed? Are you familiar with the fact that matter and energy is neither created nor destroyed? Carbon existed before as animals and other biomass, and you are saying now that the total biomass of the planet is not enough and we generated CO2 from thin air?

>It is also important to note that, even if it was physically possible to solve this problem in this way, you can tell it isn’t economical to do so, because if it was we’d already have fully (not partially) replaced fossil fuels with biofuels.

The dearman engine is zero emissions refrigeration truck, and runs on nitrogen. It is not being adopted into more developed countries despite being better, because of legacy vehicles. There are many reasons why biofuel hasn't taken off in the US but in many other countries it has.

So making more expensive technology for carbon capture is more economical? The problem they solved then was not fuel recycling, it was carbon capture. You can look it up (I'm on mobile) and state the issues with it. Even at the cost of $50 a tree, its 50 billion to stop worrying about carbon emissions.