> The first target before we think about getting back to preindustrial levels, is to get to net zero by 2050.

yes, getting to net zero is what my calculations of 13 gigatonnes of carbon per year are based on. i didn't base any calculations on the 950 gigatonnes of carbon dioxide to get back to preindustrial levels

however, a crucial point that i was missing was that your 187 million m³ was annual consumption of solid wood products; you just said 'as of 2009 the US was using 187 million m3 of solid wood products', with no denominator. but on checking out the usda link, it says

> In 2006, an estimated 6.8 billion ft³ (187.5 million m³) of solid wood products were consumed in the United States, down slightly from 2005 but more than twice the consumption in 1950.

that is, 188 million m³ of solid wood was consumed per year; that's not the total amount sequestered in the existing housing stock for 300 million people, which is how i interpreted your comment

a crucial question missing here is how long the relevant carbon stays sequestered for; if the houses get demolished ten years later and the wood rots, we've made the problem worse rather than better. but maybe it all ends up in landfills and stays there for centuries, in which case it's making a quite significant contribution to direct air capture of carbon dioxide from natural gas plants, not an insignificantly small one as i had said

(still, i don't think it'll be competitive with point-source capture from the gas peaker flue. some form of direct air capture is probably necessary for the mobile emissions sources that will run off synfuel and for drawing down the existing excess atmospheric carbon, but it can't compete with point-source capture where applicable)

> The facts on the ground are that we don't do [direct air capture and mineral carbonatation sequestration] for some reason. Most likely there are some serious obstacles. Which ones, I don't know.

you're in luck! i do know, and i can tell you:

1. there's currently no global incentive structure to do this. the carbon-offset market is currently mostly paying people to not burn fossil fuels they were threatening to burn, chop down trees they were threatening to chop down, or paying people to plant trees which might possibly sequester the paid-for amount of carbon if they somehow live to maturity and then happen to get chopped down and buried. this depresses the price of carbon offsets to the point where you can't make money sequestering carbon. for the first time last year at cop27 we got a global diplomatic agreement to set up a global carbon trading system, but governments will probably continue to fuck it up for decades, because it's a global prisoner's dilemma problem

2. specifically with respect to direct air capture (as opposed to ccs in general), point-source capture is immensely cheaper because the flue gas is 80000+ ppm carbon dioxide instead of 450 ppm, it's just hot. so, at scale, flue-gas capture will precede direct air capture by quite a long time, though there are lots of promising dac experiments which will eventually be crucial to reversing climate change. some of them involve planting forests, cutting them down, burning the wood, and using point-source capture approaches on the flue gases.

3. direct air capture requires a lot of energy, like about 10% of current world marketed energy consumption, and energy is still expensive, because pv panels have only been cheap for five years now, so most of world marketed energy consumption still is not pv. even point-source capture requires very significant investment. as pv displaces thermal power plants, electric motors displace internal combustion engines, and the much cheaper synfuels replace fossil fuels for the remaining heat engines, we'll see a dramatic boom in world energy consumption unlike anything in the last 200 years, stimulated by dropping prices. this will make carbon dioxide sequestration significantly more affordable, which greatly eases the prisoner's-dilemma problem

4. mineral carbonatation experiments are still in the pilot-plant stages; there's no question that it solves the problem (chemical weathering has been well understood for decades), but the question is, what's the cheapest safe way to do it

> The same with synfuels. (...) it shows the technology exists, but it doesn't show it is economical in the current market conditions.

i would go further: synfuels are clearly not economical in current market conditions. they are currently too expensive to compete with fossil fuels, because there isn't yet enough pv installed to meet energy demand, so you still have to pay fossil-fuel prices for your pv megawatt-hours. that's going to change over the next decade. as pv grows to dominate the energy ecosystem, energy prices will continue to drop, and as the most accessible deposits of fossil fuels are gradually exhausted, fossil-fuel prices will continue to rise, so synfuels will become the cheapest option for heat engines

there's a certain amount of risky innovation between here and there: how fast will energy prices drop? this depends on the details of how world war iii unfolds. how much demand for liquid fuels will remain? what's the most efficient way to harness intermittent pv power for process plants like fischer-tropsch? which process will turn out to be the most profitable? will ai discover radical new processes?

but it's clear why synfuels aren't competitive today, and it's clear we're headed for synfuels replacing fossil fuels, in decades, not years or centuries

> I don't think like that, and nobody thinks like that.

some of us do, and that's why humans can now speak with those not present without making a sound, why they can fly through the sky like birds, and why human life expectancy at birth is 73 years now instead of 24. join us and we can solve these problems sooner