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Planting massive amts of trees to fix climate change?

TofuRobot

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Forest Nymph

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Oh yes carbon sequestration is a powerful tool to addressing climate change, and it's MUCH safer (and better for wildlife, and probably for plants) than doing some crazy thing where they create a cloud of particulate matter to block the sun's rays (no, this is a REAL THING and it sounds dystopian, my energy and climate prof didn't even seem happy about it).

I have friends/acquaintances in Eco Resto and it's a very important component of not only fixing habitats but the Earth itself.

I have been very interested in the idea of re-greening cities having lived in LA, but it's even something that should be addressed in suburban and rural areas of the Pacific Northwest. Where I'm at is great, but Oregon is a mess of clear cuts.
 
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Jamie in Chile

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I looked into this once and it was annoyingly complex and I gave up after a few hours of reading studies and articles without reaching a definite conclusion.

However, it seems that planting trees in the tropics will probably be beneficial for global warming but it's unclear whether the same is true in the temperate regions that many of us live in. Some scientists actually believe it will have no positive effect to plant trees in temperature regions, or even a negative effect!

There are other benefits of planting trees of course.

It's important as well not to use the prospect of this kind of thing as an excuse not to slash our own personal carbon emissions.
 

Lou

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As we move away from "cow-based" agriculture, rangeland could be reclaimed by forests. Although I remember reading somewhere that rangeland isn't so bad for carbon sequestration either.
If we move away from monocultures, we might see a return of things like hedgerows, windbreaks and wood lots too.
I also think suburbs need fewer lawns and more gardens.
 

Forest Nymph

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After further reflection, I do have more to add to this. Food forests are a thing now, and are ecologically compatible with a woodland ecosystem, and so therefore are entirely vegan. Food forests are an exciting concept which could reduce both rangelands (which are absolutely terrible for the Amazon rainforest even if they have some benefit in the US middle/West as a grassland prairie, the best ecosystem is always the native ecosystem) as well as reducing huge monocrops.

I also completely agree with Jaime that this should not be looked at as an excuse to not reduce, reuse, recycle, switch away from carbon-based energy and animal ag, etc...even if we do all of those things, for political and sociological reasons they will take time and be a process, so the planting of trees and re-foresting is part of it all - it's not an alternative to moving towards a renewable, plant-based world.
 
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After reading the article, I was going to mention lawns and food forests. Looks like @Lou and @Forest Nymph beat me to it.

Lawns are the worst. Food forests are the best. If we replant with food forests, this could take some production away from the monocultures, freeing up more land and allowing more food forests to be planted. This has a cyclic effect until there's little cropland left. This is a dream, but unlikely to happen because of the scale involved.
 

Jamie in Chile

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Hm. Food forests. Interesting. Wasn't really even aware it was a thing. Sounds like a good idea at first glance although I've only thought it about for 30 sec.
 

Jamie in Chile

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OK, so I looked into this more. I think I have it figured out now. If you don't have time to read all this, the basic fact I said before remains true: to stop climate change, only plant trees in the tropics and nowhere else.

Planting trees has these effects:

1. Locks up carbon out of the atmosphere as they grow, which reduces global warming.
2. Tree leaves absorb heat, which increases global warming. If the leaves were not there, some of this heat would be reflected back into the atmosphere by the ground and ultimately lost into space. To put this another way, trees reflect less on average than the average bare ground.
3. Forests can create cloudy and rainy weather. This can cause cooling that can reduce global warming.
4. Releases some chemicals produced by the trees into the atmosphere. There is a dispute between 2 scientists about whether this causing a cooling or heating effect to the atmosphere, but it's probable that the overall effect is smaller than points 1 and 2.

All of these effects will only exist for the lifetime of the tree or the wood. Forest fires send black soot (carbon) into the atmosphere to form CO2 and cause global warming. So, mass tree planting projects would need to plan to avoid fire or keep fires small as mass fires would mean the overall effect on global warming would be to increase it.

Effects 1,2,3 and 4 vary by various factors including what type of ground the trees are planted on, what type of tree, and the location on the Earth so we cannot make an absolute judgement about whether trees reduce global warming or not that would be correct for all cases. On average, the effect of planting trees is probably fairly neutral to climate change.

We can also consider some specific cases:

A Latitude of 20 or less (tropics).

Points 1 and 3 dominate and therefore the net effect is cooling. In such regions it makes sense to plant trees to reduce global warming.

B Latitude of between 20 and 50
Points 1 and 2 are in rough balance, points 3 and 4 are smaller, and so the overall effect on climate change cannot be said with certainty to be positive or negative but is probably fairly neutral and a small effect. Some evidence indicates that tree planting in temperature regions may cause cooling on a small timescale (e.g. 10 years) but warming on a longer timescale (e.g. 50 or 100 years) as explained in point iv) below.

C Latitude of above 50

Point 2 overcomes point 1, and therefore planting trees causes more global warming. Point 3 is small. Point 4 is more likely a cooling effect at these latitudes, because of the type of chemicals emitted by boreal forests, but probably not enough to overcome the dominating point 2. This is partly or mainly because of the large amount of snow at these latitudes (mainly Canada and Siberia) in the winter, which strongly reflect heat back into space. Planting trees blocks the light path to the snow and ice, the trees absorb the heat instead. Therefore we should not mass plant trees at these latitudes. The same logic may apply to high altitude areas of temperate regions. A good guideline is that in a place where snow lies all winter, do not plant trees.

Other thoughts
i) If you live in a temperature zone, and want to plant trees to fight climate change, it makes more sense to support a project in the tropics rather than a local one.

ii) There is a large amount of uncertainty. Therefore using tree planting to offset specific numbers is not fair, e.g. if you think your carbon emissions for the year were 9.7 tonnes and a website set if you pay x dollars it will plan y trees to offset that number. Any website offering that level of precision without mentioning about the huge margin for error should not be trusted. Likewise, marketing or media statements like "buying this electric car is equivalent to planting 13,456 trees" or "China has shut down x coal fired plants, equivalent to planting y trees" or any statement that links an amount of global warming/climate change/carbon in the atmosphere to a specific number of trees are at best exaggerating the level of precision and at worst total nonsense. Especially when we factor in other questions: would someone else have planted trees there anyway? How do we know how long before they are cut down or burnt down? If you want to offset a specific amount of emissions accurately, you need to do it another way. Not with trees.

iii) Trees don't last forever, so tree planting to offset carbon emissions doesn't really offset them, it just delays them. At some point 10 or 100 years later, the carbon will likely end up back in the atmosphere. Once that happens, the net effect will have been to cause warming by then (except in the tropics) because the carbon has been returned, and the differential albedo effect - i.e. greater absorption of heat by trees vs reflection by bare ground- has caused warming in the meantime.

iv) Point 1, tree growth sucking carbon out of the atmosphere occurs primarily in the early growth phase of a tree, so planting trees has a positive effect on climate change in the first few years in most cases. The albedo effect, point 2, builds up over time. So in many cases tree planting causes global cooling in the short term but warming in the long term (but probably not in the tropics but this point is more for the temperate region).

v) Large scale forest fires in tropical regions are particularly disastrous from a climate change perspective.

Major source
It seems that much of the opinions and articles and scientific consensus trace back to a single study. This one: https://www.pnas.org/content/104/16/6550.abstract If there are errors in this study, very key points in this article including my overall conclusion could be wrong.

Other sources
https://www.nature.com/articles/d41586-019-00122-z
https://www.naturalclimate.solutions/the-science
https://www.theguardian.com/environment/2006/dec/15/ethicalliving.lifeandhealth
https://www.llnl.gov/news/models-show-growing-more-forests-temperate-regions-could-contribute-global-warming
https://forestsnews.cifor.org/24311/on-forests-role-in-climate-new-york-times-op-ed-gets-it-wrong#.VC62S2ddWSp
 
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Lou

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Nice job. But (of course) I have some quibbles.

I really don't like your conclusion about #2

Bare ground. What color is the bare ground? If the bare ground is brown or black it is going to absorb more heat than leaves.
And. bare ground is never a good idea. If you have some bare ground - plant something!

Also even if the ground is white, some of the reflected heat going up is going to be absorbed before it goes into space. Could be dust, or moisture or (wait for it) Green House Gasses.

#4. The chemicals that forest produce is something like smog. which does promote warming. HOWEVER, this doesn't even come close to the cooling effect caused by locking up carbon.

The main thing, and I'm sure I could find numbers if you insist, is that forests (everywhere and all the time) are busy locking up carbon. Maybe the exception is mature forest. There may be more decomposition than growth. I'd have to look that up. but as long as the forest is healthy, growth should exceed decomposition.

Forest fires are always bad. Many are not preventable. And some times climate change is a contributing factor. So if you decrease global warming you will have fewer fires. And if human beings were just more careful.

Really long term, eventually that carbon is going to be released in the atmosphere.

But right now we are in an emergency. Each tree planted now starts locking up carbon now. We can worry about releasing the carbon in 20 or 50 or 100 years. If we haven't destroyed the planet by then.
 

Jamie in Chile

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What I wrote is almost all from scientific research and expert opinion, rather than my own opinion.

Black ground is not very common. Planting trees outside of the tropics will on average increase the absorption of heat since on average the albedo of the forest will be more absorbing than the average ground. Yes, this may vary by ground type. Lands that produce crops and pasture lands tend to be better than forests for reflecting.

Your quibble with point 2 is ultimately a quibble with the consensus expert opinion, and also specifically this research paper: https://www.pnas.org/content/104/16/6550.abstract

"We find that global-scale deforestation has a net cooling influence on Earth's climate, because the warming carbon-cycle effects of deforestation are overwhelmed by the net cooling associated with changes in albedo and evapotranspiration. Latitude-specific deforestation experiments indicate that afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions."
 

Lou

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Sorry, Jaime. I don't buy it.

I googled deforestation and global warming and got only like a million articles that claim deforestation CAUSES global warming.

Like this one from Scientific America
and this one
and this one
and this

'nuff said.
 
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Jamie in Chile

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I agree that deforestation causes climate change, but that doesn't disagree with anything I said about planting trees, or change any of my conclusions about whether or not to plant trees in order to fight climate change because:

1. The net effects of planting trees are not necessarily the opposite of the effects of deforestation. Deforestation can be caused by fires which may release extra carbon and soot from other plants or even the ground that was caught up in the fire. Fires can also cause blackened ground which would cause more absorption of heat later (even more than the forest did before). Therefore, if the statement "planting trees does not reduce climate change" were (hypothetically) to be correct it does NOT logically follow that deforestation definitely does not cause climate change.

2. I have argued that planting trees only/mainly reduces climate change in the tropics. Therefore saying that deforestation causes climate change is clearly consistent with that, if most deforestation happens in the tropics which it probably does. The articles you shared refer specifically to the tropics.

I think the comment from above, from the research paper, is probably still a fair summary of scientific consensus: "afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions."

I think in fact what you posted above doesn't disagree with anything I said but does disagree with one sentence I quoted from a research paper, namely "We find that global-scale deforestation has a net cooling influence on Earth's climate". That sentence does indeed look dubious, and does seem to disagree with some of the articles you cited. I wonder if what they perhaps meant was to talk about the average effect of deforestation at different latitudes in some hypothetical model scenario where the deforestation would be occurring at a higher rate at the higher latitudes. If that statement is indeed wrong, I don't think it invalidates any of the region specific findings or other detail of the paper.

I would also add that deforestation is a bad thing even if it had (hypothetically) no effect on climate change. A major reason being that it would lead to loss of life through habitat loss, and even species extinctions. Probably goes without saying but doesn't feel right to have a discussion about the effects of deforestation on climate change without acknowledging this.

I would like to see some further research on the climate effects of planting trees, especially at temperate latitudes. While I am confident that my conclusions are a fair interpretation of available research studies and consensus expert opinion, that is not the same as saying I am confident that they are true. It would be interesting to see further studies done. For such an important issue, the amount of science done is quite low.
 

Jamie in Chile

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Also found this today:

"The mitigation costs through forestry can be quite modest, US$0.1–US$20/tC in some tropical developing countries, and somewhat higher (US$20–US$100/tC) in developed countries. The costs of biological mitigation, therefore, are low compared to those of many other alternative measures."
Source: Intergovernmental Panel on Climate Change (IPCC).

However I explained above that the precision of using biological offsets is very poor - see above in post #8 under "Other thoughts" point ii).

So, I'd think about it this way. If you give $10 to a tree offset project in a tropical country, that may cause, best guess, a tonne of carbon to be taken out of the atmosphere (or equivalent overall warming impact). However, you don't really know. It could be three tonnes or more or a quarter of a tonne or less.

On the other hand, if you give $10 to a non-biological project (e.g. methane capture from landfill, efficient cookstoves, handing out LED light bulbs etc), the best guess, and perhaps average result, would be that your impact would be less - under 1 tonne. However you would at least have a smaller margin for error.

So if you want to cause the maximum good (and only IF the IPCC is right), and if you are willing to take a high risk of a poor or even negligible result to get an average higher gain, tree planting in the tropics makes the most sense when you purchase offsets. On the other hand, if you want to offset more precisely or be sure that you personally have achieved carbon neutrality, it may make sense to purchase non-biological offsets.