Fact Check: More CO2 Promotes Plant Growth


Plants Need CO2

Plants perform photosynthesis; meaning, they produce biomass with the help of sunlight, CO2 and water. You might assume that because CO2 is the “main food” source for plants, that the more CO2 there is in the air the better plants grow. This assumption has been proven as true in laboratories. In greenhouses, the air is sometimes enriched with CO2 so that the vegetables can grow better. In these cases, the additional CO2 has a “fertilizing effect.”

There is also a 2016 NASA study that found that the globe has become greener, the green areas have increased worldwide, because the CO2 concentration in the atmosphere has increased by about two-thirds. This could also be perceived as proof of the “fertilizer theory.” In reality, nature is a little more complicated.

Fertilizing Effect Is Speculation

The CO2 fertilization effect has been scientifically researched intensively. The most important results that scientists found are that the fertilization effect is much weaker in the field than in the laboratory. Also, its effectiveness depends on the plant. Certain plants such as corn and millet cannot process the additional CO2 at all, so they do not grow more quickly.

In tropical forests, scientists found that lianas grow faster with an increased CO2 concentration, but they then displace other plant species like trees. This is problematic because trees are important carbon stores. This depicts how difficult it is to simply say “the green areas are increasing.” If the balance in the rainforest is more lianas, but fewer trees then this is counterproductive because although a forest rich in lianas may have more green leaves, it stores less carbon.

There have been multiple experiments, for example in Switzerland, where natural forests were exposed to an increased CO2 concentration for several years through perforated tubes that allow CO2 to escape. The result was that the trees’ metabolism accelerated, but they did not grow faster. As an explanation, they found that the trees did more photosynthesis, so they could create more sugar from the increased CO2. But this did not translate into biomass, instead the sugar ended up in the ground where it was broken down by microorganisms. In other words, if the forest were a company, the sales would have increased due to the additional CO2, but profits would stagnate.

Plants Don’t Just Need CO2

One thing must not be forgotten, no plant lives on CO2 alone. It can only process it if other nutrients such as phosphorus and nitrogen are sufficiently available, which is often not the case.

Too Much CO2 Is Counterproductive

Climate change is also leading to increased drought in many regions, and without water the additional CO2 is of no use to the plants. On the contrary, the lack of water makes them even more stressful.

In conclusion, CO2 does have a fertilization effect. However, it is at a lower rate in the natural environment and can lead to negative changes in the composition of the vegetation. As far as agriculture is concerned, the possible growth “gains” from additional CO2 are destroyed by the consequences of climate change: more unpredictable severe weather conditions, more storms, more droughts in certain regions, etc.

The question remains who benefits from fooling us with the fairy tale of the “positive benefits” of increased CO2 levels?

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