By Craig D. Idso — May 20, 2022
“Gratefully, nature does not have to wait another century or so for the air’s CO2 concentration to double before reaping benefits from enhanced water use efficiency. It has already begun to profit in this regard from the approximate 50% increase in atmospheric CO2 that has occurred since the Industrial Revolution began.”
In my last article I wrote about increased plant productivity as a key ecological benefit of atmospheric CO2 enrichment. This article highlights another well-known and near-universal impact of Earth’s rising carbon dioxide concentration—enhanced plant water-use efficiency.
In basic terms, plant water use efficiency is the amount of biomass produced by a plant per unit of water lost via transpiration. At higher CO2 levels plants generally do not open their leaf stomatal pores through which they give off water vapor as wide as they do at lower CO2 concentrations.
The smaller pore openings make it more difficult for water within the sub-stomatal cavities of the leaves to escape to the air. Consequently, elevated CO2 not only enhances plant photosynthesis and growth, it also reduces plant water loss by transpiration, which combination of factors improves plant water use efficiency.
The magnitude of this incredible benefit varies by plant and growing conditions. Nevertheless, most plants experience water use efficiency gains on the order of 70 to 100%–or more—for a doubling of atmospheric CO2 (see and read reviews of multiple peer-reviewed studies under subheadings of Water Use Efficiency here on my CO2 Science website).
As an example of this phenomenon, Figure 1 shows the effects of elevated CO2 and plant water supply on the water use efficiency of soybeans. The plants were grown in controlled-environment greenhouses for 40 days under ambient or twice ambient CO2 concentrations and one of three water treatments: well-watered, moderate drought or severe drought.
Regardless of watering treatment, the scientists who conducted this study found that a doubling of CO2 significantly increased the water use efficiency of these plants by a whopping 217 to 247%!
Figure 1. Water use efficiency (WUE) of soybean plants grown for 40 days under various water-supply treatments (WW = well-watered; MD = moderate drought; SD = severe drought) and atmospheric CO2 (ambient and elevated, elevated = twice ambient). The numbers in red text indicate the percent enhancement of plant WUE under elevated CO2 for a given water supply treatment. Source: Wang et al. (2017).
Gratefully, nature does not have to wait another century or so for the air’s CO2 concentration to double before reaping benefits from enhanced water use efficiency. It has already begun to profit in this regard from the approximate 50% increase in atmospheric CO2 that has occurred since the Industrial Revolution began.
Evidence of this fact is frequently noted in scientific studies utilizing dendrochronological methods and stable isotope analyses on long-lived tree species from all across the globe. Figure 2, for example, depicts the change in atmospheric CO2 and water use efficiency for an evergreen coniferous species in China. Since 1880, the rise in atmospheric CO2 has helped boost the water use efficiency of these trees by an incredible 60%.
Figure 2. Annual variations in tree-ring averaged intrinsic water use efficiency (iWUE) and atmospheric CO2 concentrations (Ca) between 1880 and 2014 for P. orientalis. Source: Weiwei et al. (2018).
Similar-magnitude increases in water use efficiency have also been noted in Douglas fir and Ponderosa pine from the United State, in Norway spruce in Italy and Germany, cypress trees in southern Chile, Juniper, Acacia and Aleppo Pines in northern Africa, as well as a host of other trees from numerous other locations (see many examples here). But perhaps the best evidence of a modern increase in water use efficiency due to rising levels of atmospheric CO2 comes from a key study published by Cheng et al. (2017) in the scientific journal Nature Communications.
Using a combination of ground-based and remotely sensed land and atmospheric observations, the authors of this seminal work performed a series of calculations to estimate changes in global water use efficiency over the period 1982 to 2011.
Results of their work, as shown in Figure 3, reveal that global water use efficiency increased at a mean rate of 13.7 milligrams of carbon per millimeter of water per year, experiencing a phenomenal 21.6% enhancement over this three-decade-long period, almost all of which was attributed to rising atmospheric CO2.
What is more, the authors report that this increase did not come at a cost of enhanced global terrestrial water use. Instead, rising atmospheric CO2 improved the global carbon uptake per unit of water used, meaning that plants today are larger and produce significantly more biomass than 30 years ago without needing any more water to do so, which finding holds extremely important ramifications for the future growth and survival of both plant and animal species.
Figure 3. Estimated trends in global water use efficiency (WUE) over 1982-2011. Annual mean anomalies (with linear trend line) are presented along with associated standard deviations of global WUE. Source: Cheng et al. (2017).
Finally, Figure 4 presents a spatial view of the global water use efficiency trends reported in the Nature Communications study. As is clearly evident by the various degrees of green shading, a full 90 percent of the global vegetated land area show positive, increasing trends in water use efficiency, which finding is actually quite impressive considering there were large-scale disturbances such as heat waves and droughts over the study period that should have adversely impacted water use efficiency in many regions. So why didn’t they?
Figure 4. Estimated spatial trends in annual water use efficiency over 1982-2011. Source: Cheng et al. (2017).
The reason, as you might have already guessed, is because of CO2. Thanks to rising levels of this key atmospheric trace gas, the world’s vegetation has met and largely overcome a host of debilitating influences that should have reduced plant water use efficiency in more locations than shown on the preceding map.
And as CO2 emissions from fossil fuel use continue to increase in the years and decades ahead, the observed positive enhancements to plant water use efficiency will increase even more, as the authors of this Nature Communications study further report a 10% increase in atmospheric CO2 induces a 14% increase in global water use efficiency.
So it is that nature truly benefits from rising levels of atmospheric carbon dioxide. Far from being a pollutant, atmospheric CO2 is necessary for enhancing life.
Cheng, L., Zhang, L., Wang, Y.-P., Canadell, J.G., Chiew, F.H.S., Beringer, J., Li, L., Miralles, D.G., Piao, S. and Zhang, Y. 2017. Recent increases in terrestrial carbon uptake at little cost to the water cycle. Nature Communications 8: 110, DOI:10.1038/s41467-017-00114-5.
Wang, Y., Yan, D., Wang, J., Sing, Y. and Song, X. 2017. Effects of elevated CO2 and drought on plant physiology, soil carbon and soil enzyme activities. Pedosphere 27: 846-855.
Weiwei, L.U., Xinxiao, Y.U., Guodong, J.I.A., Hanzhi, L.I. and Ziqiang, L.I.U. 2018. Responses of intrinsic water-use efficiency and tree growth to climate change in semi-arid areas of north China. Scientific Reports 8: 308, doi: 10.1038/s41598-017-18694-z.
[note from Charles]
I understand Craig Idso’s tip jar could use a bit of love.
Often not considered is the surface energy budget components related to changes to vegetation. Transpiration from leaves = cooling. The latent heat fluxes of transpiration transfer about 85 watts per square meter of heat from the surface to a height to more easily radiate back out to space. Increasing transpiration increases heat dissipation. Increasing transpiration, say 5%, would effectively put another 3 watts back out to space. Vegetation also has importance to cloud dynamics. A change of clouds of +/- 2% would also change surface energy available 3 W m-2. Leafy area is critically important because it makes the process 3 dimensional, as opposed to a flat evaporating surface. Additionally, the amount of time that leaves transpire is equally important, making the process 4 dimensional. More leaf area growing for longer periods is an important feedback, mostly negative from an energy budget perspective. Transpiration has a greater latent heat of vaporization than evaporation, making the process critically important to energy budgets. This is only gets swallowed up in parameterization of CMIP models to date so the impacts on climate are not yet being modelled adequately.
JCM: Doing mass balances is not so simple as you think. Here’s few big obvious things you shouldn’t have missed.
1 “Leafing out” has increased 35% on earth, so reducing losses to evapotrans is incorrect.
2 Since a major change in veg is fringing inwards on arid areas, what rain they used to receive was virtually all re-evaporated directly. Now, growing amounts of this rain are partly retained and partly released as new areas of evapotrans.
3 Photosynthesis is an endothermic reaction (cooling). That is sunshine itself is sequestered. How much? Well we can determine this by burning a plant. The heat this gives off is roughly the suns insolation energy that would have heated the ground and atmosphere. The shade from the plant also preserves some moisture in the soil.
Ceteris paribus (=” all ‘other’ things remain the same”) is the singlemost erroneous fundamental linear thinking and analyses that plagues climateering science . You change one factor in a system and all the other factors change to resist the change you were expecting in, say, earth’s temperature. The earths Great Greening is an excellent example.
Another: if you heat the atmosphere or the oceans they expand in volume reducing the temperature increase somewhat, but there’s much more. The energy to drive winds, and ocean currents is partly consumed. In the extreme, hurricanes and tornadoes draw warm moist air up rapidly to radiate heat out into space. Then there are clouds and thunderstorms… warm currents are cooled melting polar ice without changing temp …. here’s a rule: net feedbacks are negative.
Good effort Gary Pearse. You’re on the right track.
Clearly, photosynthesizing plants are smarter than people that create highly speculative models using RCP 8.5 that lack any experimental verification.
The former are also far more beneficial to the planet.
None of the models have any experimental verification
The greening of the planet. Mostly in desert areas. Is this news?
Nothing new here at all.
“This article highlights another well-known and near-universal impact of Earth’s rising carbon dioxide concentration—enhanced plant water-use efficiency.”
Part of a well traveled path here. Over the years, there have been many such articles on this topic here at WUWT.
While some might say better water efficiency in plants, from enhanced growth, leaf cover etc, is a good thing, the more alarmist will say reduced transpiration is a bad thing. For every good thing they usually counter with several negatives
“Two recent studies, however, demonstrate the importance of being able to consider the response of vegetation to elevated levels of carbon dioxide in climate models as we try to predict our climate future.”
…carbon dioxide’s direct effects on vegetation contribute to global warming. Through the pores called stomata in their leaves, plants take in carbon dioxide from the atmosphere that they use for photosynthesis. They then give off water through the stomata in a process called evapotranspiration which cools the plant just as perspiration cools human beings. Evapotranspiration also cools the surrounding air—a tree can transpire up to ten gallons of water on a hot day. But when carbon dioxide levels increase, plants’ stomata shrink, releasing less water into the air and reducing the cooling effect.”
Another effect of the doubled CO2 is increased runoff from the land as more precipitation bypasses the plant’s evapotranspiration system and makes its way directly into streams and rivers.”
Already, warming and increased runoff have cancelled out any benefits(sic), but the best part of Colombia’s piece:
“The Carnegie study did not take into consideration other effects of increased carbon dioxide such as an increase in leaf area, variations in vegetative distribution and resulting changes in albedo”
Unbelievable, eh. But don’t worry:
“New climate models are being designed to consider dynamic global vegetation that allows plant types to shift interactively with climate, and ecosystem demography that accounts for how communities of diverse plants might respond to climate change over time.”
Climate models don’t work. OK Computer lets make them even more convoluted.
According to USGS: “Runoff is nothing more than water “running off” the land surface. Just as the water you wash your car with runs off down the driveway as you work”
Yes, the water… “makes its way directly into streams and rivers.”
…the response of vegetation to elevated levels of carbon dioxide in climate models …
I’m fascinated by the idea of climate models with vegetation in them! 😳
If you consider pond scum as vegetation, I’ve considered climate models pretty scummy.
When water is stagnant, the scum rises to the top.
“Evapotranspiration also cools the surrounding air—a tree can transpire up to ten gallons of water on a hot day. But when carbon dioxide levels increase, plants’ stomata shrink, releasing less water into the air and reducing the cooling effect.”
That’s a good example of the “everything else being equal” fallacy at the heart of so much junk dystopian alarmist pseudoscience. Everything else is never the same. Less water loss indeed leads to plants surviving where before there was desert. That will increase transpiration. And the satellites show the integrated overall effect – global greening. So what else is wrong with the earth becoming more green – apart from the colour being “so last year!”
Lets take the size of a hydrogen atom to be = zero so to a first approximation, CO2 is a molecule that is three times the size of an H2O water molecule.
Yet bizarrely this is claimed to let less water out and more CO2 in??
The primary cause of what’s observed is, no surprises from ths corner, the soil the test plants were grown in.
To be subject to the elevated CO2 they:
Point 1 is self evident
Point 2 means that the plants were in some sort of artifiacial compost, as might be typically found and used in commercial greenhouses.
Those folks are not gonna use any cheap old muck, they are going to use compost that has been artificially enhanced with myriad nutrients.
Points coming from there:
Plants can get plenty photosynthetic water from the CO2 they draw in, hence why CO2 was classically called Carbonic Acid
Why they need/use water from the soil is to pull up other nutrients that aren’t = CO2 and water.
e.g. Mg, P, N, K, S, Fe, Co, Si, Mn etc etc
If there was is a high concentration of those things in the soil, as there is in greenhouse compost, they patently won’t need to pull so much from out of the soil using water as the carrier.
What they also use water for is to transport, anything up to 40% of all the) Glucose they make down to their roots, which ooze it out to feed the soil bacteria.
They do this because the bacteria will turn that sugar to acid – classically called Humic Acid.
= a random mix of Acetic, Propanoic, Butyric, Citric, Lactic and loads others.
What that does is to dissolve the rock/mineral fraction of the soil and so make water-soluble all the element things listed above.
But, in greenhouse compost, all those things are already water-soluble and present at high levels.
As someone said, The Plants Ain’t Dumb, so in the high-nutrient greenhouse dirt they don’t need send as much sugar down to the bacteria and can use it instead to make themselves bigger, stronger and greener.
Enquiring Minds demand to know why I am telling this and not Idso
No, I don’t have Tip Jar, I tell it for free because I care.
You left out “nutritious” After a short search here’s a link:
Environmental Health News
Rising CO2 will leave crops—and millions of humans—less healthy
Women, children and poor people will suffer most.
Increasing levels of carbon dioxide in the atmosphere will render some major crops less nutritious and leave hundreds of millions of people protein and zinc deficient over the next three decades, according to a new study.
You will have to decide for yourself if you want to believe that.
That aside, I always wondered how scientists know what the CO2 concentration was millions of years ago. I read somewhere that they count the stomata on the bottom of fossil leaves.
Some of your posts are informative and humourous but this is just incoherent. Did you miss some medication (I care too!) That more CO2 means less stomatal opening and less water loss for the same photosynthesis is hardly the stuff of controversy. Learn about stomata – you didn’t mention them in your reply.
Peta, lots of erroneous ideas in this text of yours: CO2 never was carbonic acid: its solution/dissociation in water is; plants need water to carry nutrients up from the soil but also to cool by transpiration and thus resist to the higher temperatures at midday; humic acids are not what you say, you cited some rather simple substances, while humic acids, and fulvic, by the way, are very complex organic molecules with much higher molecular weight; glucose does not go to the roots with the purpose of feeding soil bacteria: it migrates inside the plants to feed other (non-photosynthetic) tissues, or to be accumulated in reserves or in seeds; and yes, with constant daylight temperature, it will stay in the leaves and will not be translocated to other parts of the plant: this movement takes place mainly at night, the higher translocation rates are observed at 10-12 ºC, this is known since the 1940s.
Thus you are not understanding the life of plants in greenhouses: it is not a matter of more foodstuffs: it is a matter of the proportions of the different minerals; the temperature of the greenhouse; if there is a controlled environment with daily periods of increasing and decreasing temperature; and, of course, the regime of light, the photoperiod; and, of course, the replacement of the fixed CO2 (regulation of the composition of the air, be it with machinery or just by opening and closing windows); and, also, the temperature of the roots, not only of the aerial parts; etc., etc., etc.
That’s a good description of your post.
Try reading for understanding next time.
The size of the stomata are millions of times larger than either CO2 or H2O molecules. The size of the molecule has nothing to do with it.
Water is lost when the stomata are open. Thanks to more CO2 in the atmosphere, the stomata don’t have to be open as much. That leads to less loss of water.
It’s pretty simple really. When your goal is understanding, rather than trying to find something to criticize.
“Plants can get plenty photosynthetic water from the CO2 they draw in, hence why CO2 was classically called Carbonic Acid”
This is likely one of the most idiotic statements I have ever read. It is indicative of a total lack of knowledge of basic chemistry. How on Earth does a plant get water out of CO2? Please explain how CO2 provides the hydrogen atoms to create molecules of water. Carbonic acid only exists when CO2 is in solution with WATER. To call CO2 alone carbonic acid is shear ignorance. At best you can refer to CO2 as the anhydride of carbonic acid.
Blessings of the precious, life-giving, beneficial trace gas CO2 improve every aspect of terrestrial life.
Feed the Plants! Feed ‘Em!!
Models. The continued use of computer models to prove something which we should have learned in a biology class in elementary school. The climate “experts” should’ve paid attention in those classes. Plants seem to thrive in warm humid areas, not so much in arctic conditions. Duh.
Excellent and much needed article Craig.
The media’s silence on the benefits of global greening from CO2 is just as egregious as their endless prattling on any contrived disaster-de-jour from warming.
Here’s my attempt on the same theme:
CO2 fertilisation and the greening of the Sahara | Odyssey (wordpress.com)
A few more interesting references:
Rebecca Thomas and colleagues (2016) explored the mechanism for CO2 greening, finding it to be attributable to increased light use efficiency by photosynthesising leaves (NOT an indirect effect of warming):
Bond et al 2003 had shown that CO2 in air determines the to and fro between forest and grassland, via the agency of fire. In low CO2 conditions, trees grow too slowly to become large enough to survive periodic Savannah fires. But as CO2 rises tree saplings can grow faster to reach a safe size before the next fire comes along. The result is re-forestation.
More recently in 2020 Vanessa Haverd and colleagues also clearly demonstrated that increased CO2 in air, not warming, is the “dominant driver” of the plant growth enhancement that is happening worldwide, to the tune of 30% since 1900, and 47% per doubling of CO2. Now that’s a carbon sensitivity that can be believed:
One of the most quoted publications on recent CO2 greening is the Nature paper by Zaichun Chu and colleagues:
Hi, Mr. Salmon 🙂
ANOTHER excellent, well-researched, helpful, article of yours which should be published on WUWT.
Thank you for sharing.
This week, not one of the runner-up essays was published. Sigh. Maybe next week we shall see your SUPER-GOOD essay (for content AND fine writing style) published.
With empathy (and gratitude for your perseverance on these pages),
Keep patient – our moment will come, I hope! Can’t wait to see your essay.
😕 😞 😴 😴 😴 😴 😴 😴 😴 😴 😴 😴 😴 😴 😮 😃
Indeed, CO2 is plant food and a plant-resiliency nutrient.
This good article pointing out that CO2 is beneficial is, however, marred by this:
…the approximate 50% increase in atmospheric CO2 that has occurred since the Industrial Revolution began.
By using a human history event, you falsely imply that we know that the 50% increase was mostly due to human CO2 emissions. Some speculate that this is so, but, it is, as of now, unproven.
Natural CO2 sources are 2 orders of magnitude greater than human sources. Even a slight imbalance (i.e., natural source > natural sink (they are roughly in balance)) outweighs all human CO2 emissions.
Edit to say: … that has occurred [since the Earth warmed as it exited the last Ice Age]*.
*Ice core data strongly indicates that CO2 lags temperature increases (at all time scales) by a quarter cycle. Thus, it is more likely that the rising CO2 is caused by warming earth surface temperatures than the converse (i.e., that rising CO2 caused the earth’s surface temperatures to warm.)
The graphic shows pCO2 over the last 5 million years.
it’s Figure 9d from Guillermic, et al. (2022) Atmospheric CO₂ estimates for the Miocene to Pleistocene based on foraminiferal δ11B at Ocean Drilling Program Sites 806 and 807 in the Western Equatorial Pacific.
It shows a declining trend in atmospheric CO₂. Linear extrapolation shows that after 18 million years, CO₂ will have declined below 100 ppmv — where all plant life dies. Any intervening glacial ages with their 30% drop in CO₂ will only accelerate eco-death.
So, a very good case can be made that human CO₂ emissions have given the entire terrestrial eco-sphere a very much extended lease on life. It’s quite clear that return to 1000 ppm of CO₂ will grant Earth another 40 million years of green.
That’s an interesting graphic Pat; there is a very sharp and high peak just after 2.5 Mya. This looks like a possible natural analog of the current CO2 increase – suggesting that such sharp CO2 spikes can happen naturally. Can you comment on this?
The best kept secret in politics is this one, because it has been in plain sight for many years. The biosphere, from the base of the pyramid of life, will grow. It already is. Something wonderful is going to happen.
On Twitter, whenever someone points out that increased CO2 is greening Earth, an Alarmist comes along and claims that plants are growing faster due to CO2 but losing nutrients. I’ve yet to read a study, when they bother to post one which is rare, that supports this. The last study one posted I read and it indicated a few plants used for human feed were losing nutrients but it was due to lack of nutrients in the soil and genetic changes in certain plants, some manipulated by Man and others natural.
I cannot find any study to support the idea that plants grown under increased CO2 levels lose nutrients. Does anyone have any competent source that would indicate this is true or, a source specifically disproving it?
I’m not a scientist but, I suspect, the idea that CO2 depletes nutrients in plants is so absurd that no one has studied it but I certainly don’t know that is the case.
I am pretty sure crop rotation is a known technique to avoid just this but I could be wrong.
Any insight into this issue and information to counter this Alarmist notion would be much appreciated. Thanks, all.
Following is my understanding of the situation, but I haven’t got any research links stored on the computer I’m currently using.
The nutritional value of food crops in general is extremely variable. There are numerous studies that claim that the food grown by our ancestors, before the development of artificial fertilizers, was far more nutritious than most food grown today using modern farming practices and maily growth-enhancing fertilizers such as nitrogen, phosphorus, and potassium.
I recall some time ago being very surprised when I came across an article that suggested a single Brazil Nut could supply the daily amount of Selenium that a person requires for good health. Too much Selenium is not good, so I did a search to confirm if it was true that a single Brazil Nut would be sufficient.
I came acroos a detailed study which analysed the Selenium content of many Brazil Nuts grown in many different parts of the world. The amount of Selenium varied by more than a factor of ten. In other words, depending on where the Brazil Nut was grown, and in what conditions, one might need to eat as many as ten Brazil Nuts, or more, to get the daily requirement of Selenium. If there’s very little Selenium in the soil, one can’t expect there to be much selenium in the crops that are grown in that soil, and that applies to all the other minerals in the soil.
When studying the effect of increased CO2 levels on plant growth, one has to keep all other conditions the same, during a sceitific comparison, because there are so many interrelated factors which affect plant growth. In particular, the plants should be grown in the same type of soil, containing the same amount of minerals,
If the result shows, for example, a 40% increase in plant growth (or plant biomass) with a doubling of CO2 levels, then it’s understandable that the uptake of minerals from the soil will likely be less per given weight of crop, because the soil is being depleted of minerals at a quicker rate. However, the mineral and vitamin content is not less when comparing the total weight of both crops grown under different CO2 levels. The crop grown under elevated CO2 levels will still have a greater mineral and vitamin content, but less that 40% greater. Perhaps only 20% greater.
In summary, if one is enhancing growth with either increased CO2 levels, or a mixture of Nitrogen, Phophorus and Potassium, one needs to add many other minerals to the soil in order to maintain the amount of nutrients per given weight of food crop.
It is fascinating that CO2 concentration has a double whammy on desert growth. The increase in both water use efficiency and photosynthesis activity means there should be substantial growth in marginal areas, and some minimal growth in poor areas. I suspect that will also lead to increased cycling of water overall in regions like the Sahel so that increase CO2 leads to more plant growth which leads to more transpiration leading to more rainfall leading to more plant growth.
Should be interesting to see over the next couple years.
My bet is that if you go and get the charts for the area of that map that shows gray (the deserts), and pick the locations away from cities you will find that there is no warming. CO2 is equal to the rest of the world, but the warming won’t be like the rest of the world.