
Rising CO2 won't make trees grow more, study suggests - pseudolus
https://www.cbc.ca/news/technology/co2-trees-1.5000709
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nwah1
A number of problems with this method of study, and the headline is
misleading.

The real question is whether there will be more biomass and more
photosynthesis in response to more CO2, not whether individual trees grow
more. The climate skeptics don't say tree trunks will get wider, they say
there will be more plant biomass.

And also this is adding in confounding variables and saying more CO2 could
change precipitation in certain places, and thus cause lower growth. Other
studies that show more growth with more CO2 are using greenhouses to control
for confounding variables.

And even if you are trying to answer the question in terms of a holistic
analysis, you can't just study one forest in Canada and then make any kind of
conclusion.

You'd need to study trees from most of the major forests, and look at the
density of the foliage in each.

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hinkley
Several of the reports I've seen have said we _will_ get more biomass, but
most of it will be plants we generally refer to as weeds.

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nwah1
Makes sense, considering that most of the plants we have already match that
description.

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hinkley
Most of the plants in residential areas, sure (but only if you think grass is
a weed).

Not so much in reasonably well-run parks or woodlands.

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sevensor
Sounds like it's a bit more nuanced than the headline would suggest. More CO₂
only means more growth when CO₂ is the limiting factor on growth in the first
place. Water, nutrients, and sunlight all play a role as well.

~~~
justtopost
Bingo. While not usually the limiting factor in nature, it can still be a
benefit when it is. Just ask all the 1000s of pot growers literally burning
propane to produce it indoors and vent it to atmosphere. Grr.

~~~
mr337
I did not know they did that to produce CO2. Very interesting!

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maxk42
I'll point out that the sunniest parts of western Quebec get fewer than 1900
hours of sunshine annually. [1] That's fewer than any point in the contiguous
US. Cedars metabolize O2 -- not CO2 -- in the absence of sunlight. That makes
this possibly one of the most biased and possibly misleading selections
possible for both location and organism under study.

[1]
[https://www.currentresults.com/Weather/Canada/Quebec/sunshin...](https://www.currentresults.com/Weather/Canada/Quebec/sunshine-
annual-average.php)

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randyrand
Anecdote: When I artificially inflated the CO2 in my aquarium, my plants grew
like BANANAS. Something like 4x the speed, and about 2x as big leaves, etc. It
was quite something amazing.

~~~
natermer
In terms of geologic history the CO2 levels now are lower then they have been.
It's not surprising that plants respond very positively to higher rates of
CO2.

And it's been proven to be true many times.

I guess what the study is trying to address is the positive aspect of CO2
rising enough to counter the negative aspect of CO2 rising to the plant
biomass.

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mrfusion
I’d be curious how they explain the fact that greenhouses typically add co2
for faster growth?

( disclaimer I believe in global warming with all my heart)

~~~
DennisP
Greenhouses are controlled environments where everything else is abundant too.
In more natural environments, plants are limited by availability of water and
nutrients in the soil.

On top of that, plant growth can be reduced by heat stress. They also have to
contend with insects and disease, and may not have good defenses when climate
change has brought invasive organisms to the area.

~~~
dragonwriter
Sure, but what that suggests is that the existing established understanding is
correct (or at least still plausible): even if the particular trees studied
here aren't CO2-limited and don't grow more with more CO2, total plant biomass
will or at least might (outside of climate change denial fantasies this
doesn't mean increases in CO2 will automatically be neutralized by plant
growth, because it doesn't imply that the size of the effect is necessarily
sufficient to clear the additional CO2 once long-term equilibrium is reached,
doesn't tell you how long it takes plants to reach the new equilibrium when
CO2 levels have reached a new plateau, and even if it did all that wouldn't
help when CO2 levels are constantly increasing and plant growth can't catch
up.)

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DennisP
Sure, if everything else is ideal then many plants will grow more with more
CO2. Even this study's authors don't deny that; they say that other factors
will often not be ideal:

"climate change is generating warmer, drier conditions that could make them
grow less in many places"

Overall, conditions are definitely getting warmer on average, and many places
are also getting drier, sometimes with occasional very heavy rainfalls that
wash away topsoil.

Another factor I didn't mention is forest fires, brought about by drier
conditions, as we've been seeing in California.

~~~
dragonwriter
I'm not taking issue with the study or it's authors, just the presentation of
the article, which very heavily spins it, especially up front, as
contradicting the existing understanding broadly, when it really doesn't.

It's important, because the fertilizer for anti-science attitudes exploited by
groups like climate denialists is a false impression of radical flip-flops in
science conveyed by popular media which uses exaggerated contradiction to
overplay the impact of stories and draw eyeballs.

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pvaldes
Some people should stop pretending that biology is easy and straightforward.
Growing faster means taller, not necessarily wider.

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petre
Maybe it doesn't speed up cedar tree growth but it certainly affects algae and
fern growth.

[http://theazollafoundation.org/azollas-uses/as-a-
co2-sequest...](http://theazollafoundation.org/azollas-uses/as-a-
co2-sequester/)

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jellicle
Plants may grow more easily, also wildfires may burn more easily, areas may
get more water, also areas may get less water. Areas may be hotter, but also
areas may be colder. The specific results that humanity gets depends on the
particular weather patterns that we end up with, which are very difficult to
predict, and thus the future holds a great many studies and predictions, most
of which will be wrong in their specific results.

This is a subject of interest to scientists, but not to the general public,
because nothing being studied here changes the central message in the
slightest, which is that we are undoubtedly headed for climate apocalypse and
we are accelerating into it rather than decelerating.

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mar77i
Well as far as Dan Britt's talk goes, trees haven't noticeably been adjusting
for thousands of years.

[https://www.youtube.com/watch?v=Yze1YAz_LYM](https://www.youtube.com/watch?v=Yze1YAz_LYM)

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joecool1029
Related: [https://www.sciencenews.org/article/rising-co2-levels-
might-...](https://www.sciencenews.org/article/rising-co2-levels-might-not-be-
good-plants-we-thought)

~~~
pseudolus
Also related: [https://arstechnica.com/science/2019/02/carbon-dioxides-
boos...](https://arstechnica.com/science/2019/02/carbon-dioxides-boost-to-
trees-may-not-offset-its-climate-impact/)

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KorematsuFred
Study means little as it takes a specific forest in Canada. We should probably
look at Amazonian forests, California's redwoods, India's Vindhyas and
Namibia's rainforests too.

~~~
matt4077
The basics of photosynthesis are more or less identical across green plants.
All the cool evolutionary shit has been going on in preserving water and
capturing light, pointing at CO2 probably not being a limiting factor.

Even the one neat CO2 trick I remember was really a hack to preserve water:
some desert plants have a mechanism to store a day’s worth of CO2, allowing
them to close pores and prevent evaporation.

Anyway, if you’re looking for a counterexample, I’d switch environments
altogether and try again in bacteria, algae, and maybe grasses. While I doubt
there would be much of a difference to trees, the first two are at least a few
degrees further away from them in the deity’s org chart. All three categories
also strike me as possibly being more relevant than trees in terms of total
biomass, although that’s just a hunch that may be completely wrong.

~~~
averros
Different groups of green plants have significantly different photosynthetic
cycles (notably C3, C4, and CAM) which respond very differently to changes in
CO2 concentration. For C4 plants (about 3% of plants) the current CO2
concentration is at the point of saturation. C3 plants (85% of plant species,
including most trees and grasses, and staple crops such as wheat) have rates
of photosynthesis proportional to CO2 concentration to about 1000ppm or so.
(The desert plants you mentioned use CAM cycle, but overall their contribution
to CO2 consumption is small.)

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mpg33
What is the right amount of CO2 to have in the atmosphere scientifically
speaking?

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turndown
An amount similar to levels before human impact.

~~~
m0zg
There have been times "before human impact" when atmospheric CO2 was _way_
higher than it is now, though. You'll have to be more specific.

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amelius
Do plants in cities grow faster than plants in rural areas?

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matt4077
Cities tend to have more air pollution, but the difference in CO2 and O2 are
neglible.

I once ran the numbers for O2, which is proportional, and it came out to
roughly 10m of high in the atthmosphere. I. e. climb a tree in the countryside
and you’re at O2 pressure similar to a city.

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abootstrapper
I’ve heard this argument before from climate change deniers. From a laypersons
point of view I wonder why would you assume more CO2 makes trees grow more?
More oxygen doesn’t make humans grow more, in fact it becomes toxic.

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pliny
Trees are made of carbon, humans are not made of oxygen (humans are also made
of carbon).

~~~
philipkglass
By mass, trees contain more oxygen than carbon. So do humans. Water is 89%
oxygen by mass. Cellulose is 49% oxygen by mass. Dry wood contains a bit more
carbon than oxygen, but living trees do not.

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not_a_cop
The headline is clearly wrong. Maybe they should have said "current trees".
The tree tech has already been invented to circumnavigate present restrictions
in tree biological restrictions. Very clickbait-y.

