[hillz]

If a tree is planted, grows, and then for example is burned down and paved over, that'd be true. But if a tree grows and eventually dies in a forest, it'll be replaced with new trees naturally, cancelling out the CO2 leaked from the tree dying. This C02 can also be stalled by harvesting the tree and using it in some way that stops C02 from being released for a longer time than natural.

[onlyrealcuzzo]

I did some math on this, and if all the countries in the advanced world planted fast growing trees alongside all paved and unpaved roads, over 40 years, that could potentially be enough to sequester half of all carbon emitted by humans.

Given that carbon has a half life of between 20-200 years, and that we appear to be reaching peak emissions, and that a lot of estimates say our emissions should drop by 70% just given how often we replace power plants and how completive renewables are right now and are projected to be in the future -- it seems like planting trees really could be enough.

[oh_sigh]

One problem I can see right off the bat is at the trees might rec a lot of the pavement (from roots uplifting the pavement).

Walking around parts of Portland on the sidewalk is like being on a rollercoaster because of the tree roots.

[onlyrealcuzzo]

Right, that's why you'd want to plant trees with specific types of roots that wouldn't cause this damage. But it's an important thing to consider.

[armenarmen]

Could you share your math somewhere? I’m genuinely interested, and did your calculations take into account lowered cooling costs caused by tree shaded buildings?

[onlyrealcuzzo]

It did not. But I think that's a HUGE consideration, as is the potential to reduce particulates in the air dramatically.

Here's a link to the discussion: https://news.ycombinator.com/item?id=20543605 -- on mobile so I can't figure out how to get the comment URL. If you're interested, just go there and search for my username -- onlyrealcuzzo. I'd love a second set of eyes on it. Not sure the math is right.

[sokoloff]

What does "carbon has a half life of between 20-200 years" mean in this comment?

[onlyrealcuzzo]

Good question.

I've read in several places that 50% of carbon in the atmosphere is absorbed by the ocean within 20-200 years.

I'm guessing that's bad for the ocean, and maybe there's a limit, and the rate probably isn't constant. It's not a half-life at all.

[netjiro]

That is horrible for the ocean. Acidification will be killing off whole ecosystems and lead to drastically lower carbon sequestration by our oceans. As well as other horrible problems for us humans, who are still quite dependent on functional living oceans.

[jandrese]

I think the OP is saying that most trees you plant now will be dead in 20-200 years and returning their carbon to the atmosphere through natural decay. Trees end up being a temporary solution. A permanent solution basically requires us to bury the carbon back in the ground where we found it in the first place, or in some other form that doesn't decay.

[netjiro]

Please provide numbers.

Numbers are important and should be discussed transparently. Lots of variation in guesstimates, fudging, simplifications, etc cloud the issue and give drastically different "good ways forward". So, please, correct my back-of-the-envelope estimate below:

E.g. from [1]: "Following the estimations of carbon stock including above ground biomass, the total stock in the studied chestnut forests could be ordered as follows: CF3 (105.8 t C ha-1) > CF1 (102.1 t C ha-1) > CF2 (76.3 t C ha-1). The pure chestnut forest CF3 characterized with the highest total carbon stock per hectare and only 20.6 % from it is accumulated in the aboveground tree biomass."

Chestnut is one of the best carbon sequestering forest options we have. Estimate (overly positively) that this capacity cycles over 100y. Fudge down the CO2 and CH4 release from decomposition. That gives ca 100 tC/ha over 100y, aka 1tC/(ha y) or 100tC/(km2 y).

Globally we have ca 35GtCO2 or 10GtC carbon emission per year. Current forests store about 15% of that, but we are currently loosing forests at a rapid rate, and we need to not only reach neutral but also sink the 100y or so of spewing we've already fucked up. So let's keep the number at 10GtC/y.

10GtC/y would then require 100E6km2 of NEW perfect assumption chestnut forest.

We have ca 500E6km2 of total land surface on earth. That means we need to set aside 20% of all land on earth for our NEW chestnut forest. But we don't have that much land that can sustain something like this. Forest grows less well outside of humid temperate to tropical regions. E.g. Antarctica, Sahara, the steppes, boreal forest regions, etc. E.g: All agricultural land, both fields and grazing, is 11% of total land area but over one third of all culturable land, the rest of which is already mostly forest. Even if we covered all growth-possible land area that is not already forest we simply don't have enough land. And we would be out of farmland.

Based on this back of envelope calculation tree planting is not a viable solution. It's a good step in the right direction, but nothing to get the crowds overly excited about.

Instead, e.g. azolla is around 15x more potent as sequestering growth stock than forests, and it grows floating on water. Genetically engineering azolla to grow fast in higher salinity would be a better way to combat climate change. We have plenty of ocean surface area. There will be downsides to such a solution, but compare with other solutions or the horrors of what will be if we don't act...

And I'm sure someone can cook up some gm-franken-algae that is even more potent.

My point, if any, is to make sure to actually run the numbers. Get different estimates then pay skilled scientists to get better estimates. Discuss the numbers, assumptions, simplifications. Don't get the general population stuck on low worth paths when they could start fighting for more valuable ones.

And I don't propose "stop planting trees". I argue that planting trees is a good thing, but only a minor item that is overshadowing more valuable options in the general debate. We need to get people to start facing reality to the point where they can start thinking about compromises. There is no "solution" that don't require drastic changes in how we use our land and live our lives.

Side note: nuclear is the only short term low land-usage footprint solution I can see, and drastic genetic manipulation biomass or vast nuclear powered direct capture are the only long term solutions I can guesstimate. Anyone that can show me interesting alternatives?

[1]: https://www.researchgate.net/publication/285516686_Carbon_st...