How many trees do we plant to offset global warming?

Let me first start with the disclaimer that I have no science background, and that much of the literature I find out there is difficult to digest. Someone tried writing me a missive in “laymen’s terms” all about ACC on his blog, with all the counter arguments refuted and all that jazz, but it was still a bit of a wash…Also, feel free to move this thread if it’s in the wrong place!

Yet, from what little I DO understand about the situation, it seems that:
[li]We have too much carbon dioxide.[/li][li]Trees absorb carbon dioxide[/li][li]Ergo, we need more trees.[/li][/ul]

Assuming there’s no gigantic pitfall in my logic so far, I googled the concept, and on the first page found this (somewhat dated) link, which suggests that if we did seriously consider this, we would need to do it tropical regions primarily.

I found this thread, but it’s over five years old as well, so I don’t think it’s unfair to do a new one.

This site suggest that roughly five trees will cover my own personal car’s use. Coupling in everyone else’s cars, not to mention everything else we use that has CO2, anyone care to take a guess as to how many trees we’d need to plant to completely offset CO2 use at, say, 2010 levels? Do we have enough hectares of land to pull it off? Is it feasible?

The trees would have to be planted in protected areas so that the government(s) could protect them from being cut down when they mature. Is there enough government-owned land to even attempt this?

Actually, not quite. This is where different goals of groups/ people generally labelled “enviromentalists” collide: the people who want to stop climate change first and foremost are quite happy with mono tree plantations of fast-growing trees done for money, which are then cut down after 20 years to sell the trees as lumber for profit, and re-plant the same area again (making money double both from certificates for CO2 reduction and from selling the trees later).

Because you want the CO2 that the trees absorbed during their life to stay sunk, so you want the trees neither burned nor rotting, but made into lumber, furniture, houses or paper. That binds the CO2.

The people who look at the larger picture prefer real forests which serve as habitat for many species, with natural occuring species of trees for that region, growing slowly.

This is good for nature, but binds far less CO2, because in a real forest, old trees fall down and rot, releasing a lot of the bound CO2 in the process. And naturally occurring species grow slower.

Back to the OP question: I haven’t done a back-of-the envelope calculation myself*, but several nature groups and scientists did and from what I remember, the general impression was that it’s too little too slow, if we also don’t cut way down on the current production.

Esp. since this might be good for the first 10 or 30% of CO2 in the air; but as the temps. rise, plants fight, too: their genetics is also affected by UV rays **; drier and hotter temps. affect trees. So you need to plant a lot of heat-resistant trees.

And you can’t plant trees in all areas - most don’t support trees; most of the good earth is used for agriculture to feed people (or to grow cotton, bio-diesel and other stuff). In the areas that used to be forest, once it’s been cut down, usually the thin layer of humus has been swept away leaving bare rock or similar, so you need to re-built the humus layer before you can grow trees. Which costs time and money. (They are currently experimenting with black Earth, which the Indians in South/Middle America invented. This means combining coal with compost for quick and permanent humus layer. Additionally, with a new process to gain coal, far less CO2 is emitted than bound. This could be used to re-fertilize currently barren grounds, if large tests keep the promise of the small tests).

  • Surely one of our better-at-math dopers will come along and do so?

** Yes, the ozone layer is a separate problem - but it is factored into the considerations

I thought about this too. My first idea to rectify this was to have private NGOs buy more land, and use it to create more forest land without threat of forestation. Again, I come here to tease out ideas re: feasibility and possibility. :slight_smile:

Cool! I’ve planted at least 30 trees since we moved in here a decade ago, meaning I’m entitled to several more cars.

I log old growth, so I’m way ahead on my carbon footprint. If only the rest of you could get your act together and become as environmentally sound as myself.

Just a few random thoughts:

Chainsaws, lumber mills, trucks to transport the lumber and finished products, furniture factories, and so on produce carbon dioxide, too.

And wouldn’t the ready availability of all the additional lumber drive down prices thereby encouraging people to discard and replace perfectly serviceable (but old) furniture and other wood products? The discarded products would then end up rotting or being incinerated.

Does anyone do this level of analysis?

And just one little forest fire means all that CO2 goes back where it came from and you have to start all over.

If I’m not mistaken, I believe that phytoplankton is the primary source of our oxygen. Wouldn’t we be better off doing something to promote phytoplankton growth? (But what?)

That’s five trees growing for 200 years to offset 1 tonne of emissions. In their example, the car had about 3/4 tonne emissions per year. So you need to plant about 4 trees every year, and ensure they each grow for 200 years. And then ensure that the carbon in that wood stays sequestered from then on. ETA: Also, if in the meanwhile, before the trees have offset your car’s emissions, the carbon you added to the atmosphere helps warm the planet, causing permafrost to melt, or other feedback effects, you need more trees to handle that as well.

My point being, it’s not as simple as just planting a handful of trees.

A quick search for “phytoplankton growth” suggests that the little buggers seem to be suffering from an iron deficiency, and are dying off in some sort of level (the numbers are disputed), from ocean warmth. I suppose we could always try breeding a heat resistant variety–hothouse phytoplantkon, if you will!

This is not as easy as you’d think. What’s the average lifetime of goods made from fast-growing (soft) wood? I highly doubt it’s more than a few decades. Lumber and houses are going to last the longest, but even then it’s a fairly rare house that lasts 100 years. We’re not really building for that kind of longevity any more. And furniture? Beautiful pieces made of hardwood might last hundreds of years, but the stuff I buy at Ikea isn’t going to dodge the landfill for more than 20 at the extreme outside. Paper’s even worse. I’d be very surprised if the half-life of paper was more than a year.

Growing trees for quick economic use is fine as far as it goes. Whatever manages to endure will sequester carbon, and wood furniture can be aesthetically pleasing. But short-term goods like that aren’t going to offset a major amount of carbon, and they aren’t a long-term solution to global warming.

Isn’t that a good thing, though?

Here’s the way I understand it.

  1. plant trees.
  2. trees grow, absorbing CO2
  3. trees get cut down and turned into paper
  4. plant more trees to replace them
  5. paper gets used up.
  6. used paper ends up in landfill.

Doesn’t that remove CO2 from the atmosphere permanently? If the paper, and old broken wooden furniture end up underground, then that’s some carbon that is taken out of the cycle. As long as it comes from renewable sources, and they keep planting more trees to replace them.

No. You’re missing the next step:
7) Paper in the landfill rots, which releases the carbon back into the environment.

Then, go on to the next step. Produce the methane from the landfill and use it for power generation: Landfill Gas

Paper rots, but not very fast, especially when buried in a landfill. That’s actually a problem as it clogs landfills almost as badly as plastic does. Also, the world burns something like 80 million barrels of oil per day. There’s just no way we could offset that by stuffing paper in landfills, even if we could find enough landfill space to do it.

Wouldn’t it be trapped underground, though?

No, it rises. That’s the entire reason that oil and gas production is even possible. The hydrocarbons migrate toward the surface until a trap of some sort (ex: a fault) causes an accumulation. A few feet down in a landfill is not going to contain them.

Sure. If that can be done economically, then great.

But it doesn’t help fix the carbon, and I doubt it replaces a sizable amount of the carbon we’re pulling out of the ground all the time.