Why burn them to charcoal? Living trees continue to be efficient carbon sinks for potentially hundreds of years. If you have to cut them down you should use the material for construction, to reduce dependency on energy-intensive steel and concrete industry.

But it’s a moot point anyway, because trees simply grow too slowly to be an effective carbon buffer at the timescales that are relevant right now.

You burn them because that prevents decay from releasing CO2, stabilizing the carbon for at least a millennium. Young trees also add biomass much faster than old growth.

Using them for building material is okay as well, but the amount of wood needed to get rid of the excess CO2 is far above any reasonable demand for building material. (We're talking about a trillion tons of carbon here)

”Young” here still means ”decades old” (and large, mature trees keep growing thicker fairly consistently which leads to carbon fixation to be a superlinear function of tree age). Plus recent research indicates that old-growth forests actually continue adding biomass quite efficiently. So any planted trees should at least be allowed to grow a lot longer than your standard tree plantations.

Whatever you do with the biomass a hundred years from now doesn’t really matter; either climate change is in control by then or the humanity is screwed.

What about vegetal roofs ? not strong enough ? because there's a huge surface area to tap into.

The surface area of a roof is tiny in comparison to planting miles and miles of forest. It's also very weight sensitive, but the goal is to capture, remove, and continuously replace a huge mass of solid carbon. Finally, green roofs select succulents and other plants that grow slowly, but for this goal you want a species that grows like a weed and produces literal tons of biomass that have to be trucked away and be buried.

The "plant trees for charcoal" idea is basically the bio-engineering method of "build huge photovoltaic solar plant, use electric energy to power chemistry to convert CO2 to oil". Photosynthetic plants are pretty efficient, compared to silicon solar cells, and they're (literally) dirt cheap.

but it's also quite close to CO2 pollution since a lot of emission are in cities (low efficiency use of ICE I believe)

The global CO2 production dwarfs what you could do with trees, I'm fairly certain even if we planted a tree on every square centimeter available, it would not be sufficient to counter our production sufficiently.

What we need is to invest in technology to reduce CO2. Nuclear fusion/fission, solar, wind, electric or alternative fuel cars, redesign CO2 industry processes, etc.

The petrol and coal industry would have to go entirely bankrupt. No exceptions.

If you understand French, there's an engineer called Jean-Marc Jancovici who is deep into the 'nuclear is the only solution so far'. He made talks on youtube on how to decarbonate economies.

I don't think nuclear will be the only solution, solar and wind may be useful in a post-fusion-energy world.

his point is that by looking at numbers, solar and other renewables are orders of magnitude off from being enough. With today's energy consumption of course. If we change our ways, models can be remade.

Just having the biomass is nice, but the crucial step is turning it into charcoal. Roofs also don't produce a lot of biomass per area.

Ok, I get it, too little. But I heard it's also good for insulation.

Sure go for it if you have a house. It looks really nice too. It just doesn't do too much for global warming.