Another week and another incorrect news article about climate change. I’m starting to enjoy this – reading something, checking to see whether it’s correct (isn’t this what the sceptics are supposed to do?) and discovering that actually, the facts are wrong, biased, misrepresented or misquoted.
The article in question is in the Wall Street Journal and is written by an adjunct professor of engineering – Harrison Schmitt – and professor of physics at Princeton – William Happer. William Happer is also Chairman of the Marshall Institute, a right-wing organisation which receives funding from Exxon Mobil.
The article, In Defense of Carbon Dioxide, says global warming has paused over the last decade. Peter Hadfield has debunked this myth on his Youtube channel in “no warming for 15 years“, so I won’t bother addressing that. The second claim is that there’s very little correlation between CO2 and global temperature. Peter Hadfield also addresses this in detail in “The evidence for climate change WITHOUT computer models or the IPCC“. I want to limit my discussion to CO2 and plant growth, so if anyone is interested in these other claims, I recommend Peter Hadfield’s videos.
The main gist of the article is that carbon dioxide will be good for plants. The idea behind this is that plants use carbon dioxide (CO2) in the air for photosynthesis to make energy and carbohydrates. In simple terms, more CO2 -> increased plant growth -> increased agricultural productivity -> more food for animals to eat.
The article also says that plants will require less water and so will be better able to survive dry conditions. From my understanding, the logic goes like this: plants have tiny holes in their leaves called stomata through which CO2 enters but water is lost. Plants can control these stomata: they open them to increase CO2 uptake but close them to reduce water loss. As atmospheric CO2 rises, stomata close thus reducing the amount of water that is lost.
This all sounds very straightforward and sounds like a nice benefit of global warming, but how accurate is it?
Biologists ought to know more about this than physicists and engineers and yesterday I discovered – through a family member who works in the field – that they’ve been conducting experiments on just this topic. There’s an excellent summary of this research online in, Effects of Rising Atmospheric Concentrations of Carbon Dioxide on Plants.
The experimentation is done using a method called FACE: free-air carbon dioxide enrichment in which plants are grown outside and exposed to higher than current levels of CO2. Observations are then made about plant growth and plant chemistry and physiology. This enables the growth of plants to be observed in open environments rather than in laboratories and so hopefully provides more accurate results.
What did they find?
Yes, higher CO2 levels do enable most plants to grow faster and this did result in higher agricultural productivity for crops such as wheat, rice and soybeans. But there is a downside: protein concentrations in the tissues of these plants decreases and so too do minerals of nutritional importance including calcium, magnesium and phosphorus. So while crop yields might increase, the quality of the crop decreases and so animals feeding on these crops will need to eat more of them to compensate for the loss of nutrients.
Not all plants experience faster growth with increased CO2 concentrations. Some types of plants, called C4 plants, show no increase in crop yields when CO2 levels are raised. This group of plants includes important crops like maize (corn), sugar cane, sorghum and millet. While the number of C4 plant species compared with C3 species is low, the area they occupy on Earth is large. The enormous tropical grasslands of Africa and South America are C4 plants and these will not benefit much from elevated CO2.
The plants that do respond positively to elevated CO2, a group known as C3 plants, also respond negatively to increases in temperature. Since there is a strong correlation between CO2 and global temperature, the corresponding rise in temperature as a result of rising CO2 is not good news for those plants.
The article also suggests the water requirements of plants will decrease, enabling them to better survive dry conditions. FACE experiments show water use by plants does decrease with elevated CO2, and in some cases by as much as 20%. So on this issue, Happer and Schmitt are correct, but they fail to address a consequence of this which is higher soil moisture levels and increased runoff, both of which will have consequences for the water cycle on which entire ecosystems depend. I’m not saying whether this is good or bad, just that its a little naive to suggest this is going to increase agricultural output. The story is more complicated than that.
The growth of plants is inordinately complex and depends on a great deal more than just CO2 concentrations in our atmosphere. But one thing is certain: rising CO2 is going to have a huge impact on the plants on which we and other animals depend. The consequences are tangled up in a web of changes that include growth rate, plant physiology, the water cycle and the structure of plant communities: most of which is completely ignored by Happer and Schmitt.
Source:
Effects of Rising Atmospheric Concentrations of Carbon Dioxide on Plants
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