Guest essay by Eric Worrall
A PNAS study claims that crop yields will fall by up to 7% for each degree celsius of global warming, assuming no CO2 fertilisation and no adaption measures.
Climate change will cut crop yields: study
August 15, 2017
Climate change will have a negative effect on key crops such as wheat, rice, and maize, according to a major scientific report out Tuesday that reviewed 70 prior studies on global warming and agriculture.
…
“Each degree Celsius increase in global mean temperature is estimated to reduce average global yields of wheat by six percent,” said the report.
Rice yields would be cut by 3.2 percent, and maize by 7.4 percent for each degree of Celsius warming (almost two degrees Fahrenheit), it added.
“Estimates of soybean yields did not change significantly.”
…
Read more: https://phys.org/news/2017-08-climate-crop-yields.html
The abstract of the study;
Wheat, rice, maize, and soybean provide two-thirds of human caloric intake. Assessing the impact of global temperature increase on production of these crops is therefore critical to maintaining global food supply, but different studies have yielded different results. Here, we investigated the impacts of temperature on yields of the four crops by compiling extensive published results from four analytical methods: global grid-based and local point-based models, statistical regressions, and field-warming experiments. Results from the different methods consistently showed negative temperature impacts on crop yield at the global scale, generally underpinned by similar impacts at country and site scales. Without CO2 fertilization, effective adaptation, and genetic improvement, each degree-Celsius increase in global mean temperature would, on average, reduce global yields of wheat by 6.0%, rice by 3.2%, maize by 7.4%, and soybean by 3.1%. Results are highly heterogeneous across crops and geographical areas, with some positive impact estimates. Multimethod analyses improved the confidence in assessments of future climate impacts on global major crops and suggest crop- and region-specific adaptation strategies to ensure food security for an increasing world population.
Read more (paywalled): http://www.pnas.org/content/early/2017/08/10/1701762114
This is a good example of climate hype.
The authors of the study did the right thing, they explained their study ignored real world factors such as adaption, genetic improvement and CO2 fertilisation. There is a place in science for careful studies which seek to adjust just one factor, to study the impact of that adjustment. But their study has been spun into a narrative of failing crop yields.
In the real world, any deficit is more than compensated by the factors the study excluded.
CO2 fertilisation has a dramatic effect on plant growth. The slight rise in CO2 levels to date has measurably greened the world. Commercial greenhouses take this a lot further; they burn vast quantities of natural gas and discard the heat, just to produce enough CO2 for their plants to maximise growth – usually around 1000ppm, more than double current atmospheric levels.
Genetic improvement, production of species such as dwarf rice, can have a huge impact on yield. The world may be on the cusp of truly decoding the genetic blueprint, of an unprecedented level of understanding and control over crops and farm animals. There is plenty of scope for further advances.
As for adaption – down here on the edge of the tropics, we have a simple adaption we use to grow temperate vegetables which can’t tolerate our tropical Summers; We plant them in Autumn. The vegetables grow happily through our very mild winters, and fruit in Spring, before the Summer heat kills them.
I suspect a lot more global warming would be required to allow temperate Northern Hemisphere farmers to plant tomatoes unprotected outdoors in Autumn.
Edit (EW): The following image demonstrates the dramatic effect of CO2 fertilisation on plant growth.
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So… assuming reality is totally different from what is observed.. we might have a problem.. What a spectacular bunch of crap.
Your comment is not only perfect for this article, but it is a perfect statement for the entire AGW scare.
**IF** Fossil..fuelled power is wholly replaced by Renewables, we will move from Agricultural Production to Electrocultural Production requiring vast transfers of land..base from the former to the exigencies of the latter … did I read here an area equivalent to the total N and S American continents, with much of Africa thrown..in?
So, Mega..Morons On the Green side, where is the agricultural land lost to Electrocultural primacy going to be replaced??
“Ah! The solar ranches are lost to ag. production, BUT we can farm round the windmill towers!!”
Wrong …. by the time the tower density has been mazimized, and the access easements set..aside, and the network of connectivity and telemetry cabling set..aside in alienated strips, and the massive Musky Battery Storage Warehouses located, and the concomitant Switchyards added, there will be precious little ag. land left for substantive and efficient production.
The countryside as we know it today will be horizon..to..horizon Electroculture with nary a farmer or a wheat..stook or a peasant, rabbit, pheasant, or other avian creatures to be seen. In other words, an Electrocultural natural disaster and Industrial Park covering former idyllic ‘scapes of pastoral bliss, hills, moors, and mountains.
In retrospect, people will ask why we spread Electroculture all over the landscape, drastically reducing ag. productivity. Why don,t we revert to producing power in centralized locations in things called Power Stations, using nuclear power, and restoring the countryside to its Park..like amenity for all.
Ross King tienes razón en casi todo lo que comentas,te equivocas en lo de la energía nuclear…..hay una mínimo posibilidad de desastre nuclear pero si se llega a producir las consecuencias son desastrosas,ya comprobamos con Chernovil y Fukushima,la contaminación y los residuos radioactivos nos afectan por miles de años,,por esto la energía nuclear no es recomendable. La SOLUCIÓN es un novedoso e interesante SISTEMA para producir abundante energía eléctrica y barata,sumamente barata.Para fin de año se lanza al mercado esta manera de generar electricidad.No afecta a nada ni a nadie,puede funcionar las 24 horas del día no importa que no haya sol o viento.no importa que haya sequía o llueva mucho y NO CONTAMINA….ES EXTRAORDINARIO.
I think that’s pretty accurate extrapolation there, Ross. I intend to grow vines up the sides of the windmills and hire midgets with ladders to look after harvest. Midgets so they don’t lose their heads to the blades and ladders so they can get to the top fruit. Just don’t give away my secrets, Ross! Those Green guys are always looking for mitigation! Mitigation, man! That’s all we need!
That shoulda been a John Lennon song. Mitigation is all we need! Not overly catchy, I admit.
Ya, forget minor things like the highs are not getting higher, the northern latitudes would get more temperate opening up huge tracks of land that can’t be cultivated now. More BS even if the premise was correct.
Sorry, I think that’s “huge tracts of land”. Ala- Monty Python.
Here’s an idea if we are really worried about food crop production. Why not stop the inefficient nearly valueless program to convert corn into fuel ethanol? It might also make it appear that we really care about food scarcity in those regions of the world unfortunate enough to know what it means to go hungry.
Huge crops, record storage signal more woes for grain merchants . . .
http://www.stltoday.com/business/local/huge-crops-record-storage-signal-more-woes-for-grain-merchants/article_535fed5f-6f6f-523c-849b-72e17044aeab.html
The following article which highlights record crops in India says everything you need to know about the future of crop yields. I’ll back the real world against models any day.
Since 3.5 billion BC!
More is better, up to about 1300 ppm, after which no further greening occurs.
Although pteridophytes and certain conifers do better in humid atmospheres with 5000 ppm. I was speaking of most crop plants. We don’t need to go above 1000 ppm to optimize most important plants.
Unfortunately, we’ll never get there. Outdoor CO2 levels are unlikely to ever get much above 600 ppmv, because fossil fuel supplies are not limitless, and because there are powerful negative feedbacks which remove increasing amounts of CO2 from the atmosphere, as CO2 levels rise.
I’ve read that most greenhouse operators run their greenhouses at 1200 to 1500 ppmv, because that’s optimal for C3 plants. That’s most crops, including wheat, rice, all vegetables, all nuts, and nearly all fruits except pineapples.
CAM plants (mainly pineapples & cacti) also benefit from extra CO2, but I don’t know what the optimal level is.
C4 plants don’t benefit much from extra CO2 except when under drought stress. The C4 plants are corn, sugar cane, sorghum, millet, some warm-climate turf grasses, and some weed grasses (like the dreaded Japanese Stiltgrass).
Dave,
CAM and C4 plants might not benefit from levels higher than now at all. Not sure about that, but they can survive and thrive on remarkably low concentrations of CO2.
Commercial greenhouses can be as low as 1000 ppm, depending upon the plants. I suppose a tree nursery might run higher.
Depends upon species, but the marginal gain in going from 800 to 1000 ppm isn’t usually all that much. But 800 is way better for C3 plants than 400 ppm.
I too doubt that we’ll ever get much above 600 ppm, if at all. Even burning all currently economically recoverable known FF reserves over the next three centuries probably wouldn’t do it.
I was surprised recently when I searched on the co2science.org web site and found that studies show that pineapples and cacti do apparently benefit a lot from extra CO2. Here’s a paper:
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-3040.2000.00588.x/full
The Abstract begins:
Here’s a paper about pineapples:
http://journal.ashspublications.org/content/122/2/233.full.pdf
Excerpt from the Abstract:
Note: “µmol/mol” == ppmv.
Here are some papers about cacti:
1. Nobel & Hartsock. Short-term and long-term responses of Crassulacean acid metabolism plants to elevated CO2. Plant Physiology, 82: 604–606. (1986)
2. doi:10.1016/0168-1923(91)90095-8 (1991)
3. PMID:12231958 (1993)
4. doi:10.1111/j.1365-3040.1994.tb00322.x (1994)
5. PMID:12226228 (1996)
6. doi:10.1006/jare.1996.0100 (1996)
7. doi:10.1093/aob/mci034 (2005)
8. doi:10.1104/pp.107.103911 (2007)
Here’s an excerpt from the abstract of the first reference:
Note #1: “Microliters per liter” == ppmv.
Note #2: From the paper it appears that they didn’t test above 650 ppmv.
Dave,
I stand corrected as to CAM. I was a little unsure when including those plants in with C4.
It surprised me, too, Gloateus.
What is the best answer for the problem of man-made climate change? Renewables? A carbon tax? Geoengineering? Forced life-style reductions? Carbon trading treaty’s? A stronger centralized authority overseeing decisions? Absolutely not! In fact, all of the solutions that are always talked about will likely make everything worse and have no measurable effect on climate.
From the very beginning, the most effective, efficient, rational and inexpensive thing to do about man-made climate change is for everyone to have the freedom and power to adapt!
Perhaps the biggest issue with AGW is that no one can know just how much of it there will be, or how it may manifest. Adaptation is the only method of dealing with the issue that simple takes the unknown in stride. We are always adapting to our world all of the time anyway, especially economically and politically. We must, if we are going to survive. Adapting to a few degrees of warming over 100 years would be a piece of cake! And in the very likely event that it doesn’t warm that much or not at all, we would not have wasted a second or a single penny on preparing for something that was never going to happen.
Adaptation also opens the door to a vast amount of opportunity for life enhancement! The U.S. was the world’s shining example of the opportunity that lies in adaptation (in an environment of relative freedom). People came here by the millions trying to escape the status quo. It was different, but they adapted and the vast majority thrived. Usually, the actual climate was also much different, but they adapted very quickly to the new weather pattern; and thrived!
Climate change, as projected, is almost imperceptible, compared to the vast amount of change we adapt to through the course of our lives. This is true for individuals, neighborhoods, cities, states and countries. We adapt as we need to, based on what is actually happening. This is done most efficiently when each layer of society has freedom to choose what is best for them. The great socialism experiment (that is still going on), has shown conclusively that a powerful centralized authority will always be worse than a society built on individual liberty. It is not about good or evil. It is about adaptability and efficiency! A powerful, central authority will always be slower and far less efficient in dealing with changes than free individuals choosing what is best for them (under the rule of law), through a free market.
This article looks at what would happen if we assume no farming adaptability. This is very much like the rest of the discussions of climate change action. The solutions put forth are largely based on an assumption of no adaptability to climate change, and, therefore, a need to prevent those change at great cost. This is a false basis for the discussion! Not only do these solutions ignore our greatest asset, but they promote the type of centralized decision making processes that usually lead to great harm of the very thing they were created to protect. In the end, local people will adapt to their local conditions anyway, but if they have given up part of their wealth and power to a centralized government, they will be less able to adapt to actual changes in real time, and they will suffer greatly and needlessly.
See how easy that was?
And how much easier would it be if you had 50-100 years to do it?
Jclarke 341 se producen fallas cuando el que dirije NO SABE Y SOLO SUPONE y lo peor…..se enoja cuando alguien QUE SABE LE CORRIGE. Todo lo que los científicos del clima están hablando hoy sobre las causas del Calentamiento Global – Cambio Climático es en base a nuestra TEORIZA pero cuando lo compartimos en 2012 los científicos de clima nos criticaron,nos ofendieron. En nuestra TEORÍA demostramos que el Calentamiento Global empieza 15-20 años antes de fin de siglo y termina en los primeros 15-20 años del nuevo siglo y la causa son las ERUPCIONES VOLCÁNICAS 60% SOL 30% HOMBRE 10% se termina el calentamiento y el clima del planeta es controlado por SOL 60 % ERUPCIONES VOLCÁNICAS 20% HOMBRE 20% Todo es cíclico,cada fin de siglo se produce el Calentamiento Global pero cada vez es mas fuerte. Las GRANDES ERUPCIONES VOLCÁNICAS se producen a fin de siglo.
You’re right.
James Lovelock’s Gaia hypothesis and Daisyworld model apply just as much to humans as to any other organisms. Our hubris likes to imagine that we are godlike creatures elevated above the mortal world. But we are not.
Hmmm….again, what problem with climate change?
I can only assume organisations paywall research to avoid widespread analysis and review of their research findings. The commercial value of the science or pay per view must be utterly trivial. This is not how science should work but but has the makings of a a secret society accessible only to the ordained.
If the time to adapt was measured in decades, there may be an argument for mitigation action now.
But crops like wheat, rice etc can be changed annually in theory. Allowing (say) 5 years for a transition would be entirely adequate – farmers are a conservative breed generally, genetic changes take time,and changes to varieties planted.
The report can only be regarded as utterly pointless as it ignores adaptation and mitigation which is entirely feasible and likely, could potentially increase crop yields.
The USDA publishes “Crop Production Historical Track Records” every year. The report includes virtually any crop you can think of, and the records date back to the 1800’s.
http://usda.mannlib.cornell.edu/usda/current/htrcp/htrcp-04-13-2017.pdf
The yield for most crops has increased dramatically since 1950. That’s the same period in which atmospheric CO2 has increased significantly. As an example, the yield for corn has risen as follows:
Year Yield
1950 38.2 bu/acre
2000 136.9 bu/acre
2016 174.6 bu/acre
They’re right – the climate change that is ahead will indeed cut crop yields. Famine always follows the heels of climate cooling.
BTW the equatorial ocean heat content is falling at an unusual speed, some kind of La Nina might be on the way:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/heat-last-year.gif
And the relentless cold anomaly emanating from Antarctica will eventually turn global temperatures into decline:
http://weather.unisys.com/surface/sst_anom.gif
Yet another “scientific” study showing that if your grandmother had wheels, she could be a taxi cab.
… and if frogs had wings, they wouldn’t have to bump around on their asses.
Since 1950 Indian grain production has increased five-fold, thanks to better farming methods, better transport and storage and thanks to increased levels of CO2. This PNAS study is quite in line with Paul Ehrlich’s failed alarmist end-of-times predictions of Global Famine and deaths. For the same reasons in Ethiopia, and because of increased political stability and peace, the current drought has not resulted in the starvation of millions as seen in past droughts.
The PNAS Study is real, only in the Computer Model World.
Let them eat models!
Maybe I should have thought twice about that statement.
Models: good and good for you!
https://tse2.mm.bing.net/th?q=Gisele+B%c3%bcndchen&w=120&h=120&c=7&pid=1.7&mkt=en-US&adlt=moderate
A bit of science might be worth considering about this subject. See Sage & Kubien’s (2007): “The temperature response of C3 and C4 photosynthesis”; free full text = http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2007.01682.
I suggest laymen interested in C3 plants first try to find paragraph about how heat impacts the enzyme Rubisco activase leading it’s dynamic form to degrade into non-dynamic forms (monomers & dimers) & thus leaf experiences poor levels of ready for work Rubisco. There is an example of how a plant (wheat) can compensate somewhat by splicing from the gene a more heat tolerant form of the enzyme (laymen could look for “isoform” & the abbreviation “kD”).
And furthermore can suggest laymen then try to find paragraph about how heat impacts the electron transport chain leading to light harvesting antennae drawing away from photo-system 2 (PSII). There are other dynamics there as well, like less electron transiting PSII & deficit of NADPH for toggling balanced reactions.
Since original post is not about CO2 I am not attempting to parse that myself. There is incidentally some mention on certain stomata response variability for those who are thinking about how elevated CO2 influences stomata.
Since now reviewed some other comments think this is my logical place to add details of a popular C4 crop, maize corn. It’s optimum temperature for Rubisco bring fully activated is around 28°C & yet because of how C4 deal with CO2 internally (concentrates) total photosynthesis holds steady up to 37.5°C.
If temperature goes up little by little to 45°C maize can still perform 50% of it’s optimal total photosynthetic capability. But quickly raising temperature to 40°C (where C4 Rubisco activase enzyme “denatures”) knocks down total photosynthesis to only 58% of what it would be at 28°C; while quick jump to 45°C causes drastic Rubisco inactivation.
See on-line free full text of (2002) ” Sensitivity if photosynthesis in a C4 plant, mauze, to heat stress”. And the authors do address the factor of elevated CO2 as well.
Quote: “… increasing … CO2 around maize leaves to 1,200 microbars did not affect the Rubisco activation state or altrr the effect of high temperature ….” Which leads me address the common
observation here how greenhouse growers ramp up CO2 for productivity – in greenhouses they manipulate temperature to match their crop’s temperature optimum.
It’s pretty amusing. The paper says, “Crops are sensitive to climate change, including changes in temperature and precipitation, and to rising atmospheric CO2 concentration (1, 2). Among the changes, temperature increase has the most likely negative impact on crop yields … Meteorological records show that mean annual temperatures over areas where wheat, rice, maize, and soybean are grown have increased by ∼1 °C during the last century…”
So, how did crop yields change over the last century of rising temperature? Merely up by factors of 2-4.
See also, G. F. Warren Spectacular Increases in Crop Yields in the United States in the Twentieth Century Weed Technology 12(4) (Oct. – Dec., 1998), 752-760.
Here’s how the paper starts out, “ About 15 years ago, I heard several speakers saying that our crop yields were “leveling off.” This stimulated me to assemble data on the subject. The result is shown in Table 1, which gives the U.S. average yields for 10- yr periods during this century for nine crops. The increases are spectacular, varying from two- to sevenfold.”
So, according to Zhao, et al., “ Results from the different methods consistently showed negative temperature impacts on crop yield at the global scale, …,” despite the evidence that a centennial temperature increase of 1 C — pretty typical of AGW scariness — saw huge increases in crop yields.
There’s no accounting for no accounting.
“Although pteridophytes and certain conifers do better in humid atmospheres with 5000 ppm. I was speaking of most crop plants. We don’t need to go above 1000 ppm to optimize most important plants.”
A lot of these comments focus on increased Carbon Dioxide in the atmosphere. No doubt if Earth warms 7 degrees Fahrenheit particularly in the Northern locations it will cause more growth and CO2 and heat stored in crops and trees in Siberia for example. This could lead to an increase in fires and decreased rain in southern locations could off set gains in Northern locations.
With increased Carbon Dioxide comes increased heat and decreased rain in southern locations in USA and Africa. We should save gas for a rainy day and use as fertilizer when good options like lower cost solar and gravity motors are cheaper in the long term. Looking at 1 variable like CO2 levels the atmosphere might too simplistic. I hope I wrong. Thousands of people were killed in a heat wave in Russia in 2010 and it can get too hot. A lot of Carbon Dioxide has been put into the atmosphere since 2000 and there is a lag in heating and it keeps getting hotter. So we need to find out if studies of global warming accounted for increased plant growth due to increased CO2 and if crop gains in the North will make up for decreased crop gains in southern location in USA and Africa due to drought. There are many variables in global warming. Bugs and plant diseases will move North and caused increased spraying and amount of refuge acres…..
“Russian President Dmitry Medvedev declared a state of emergency in seven regions, and 28 other regions were under a state of emergency due to crop failures caused by the drought.” 55,736 killed in 2010 heat wave in Russia from smoke and fires. I would think studies on global warming account for increased plant growth due to increased carbon dioxide and do these posts account for droughts heading north and being more often there too. If someone was part of those studies or can get that information please post. https://en.wikipedia.org/wiki/2010_Russian_wildfires
As much as I’m enjoying three summers in a row with no need for an air conditioner running up my electric bill, I’m not real keen on running the furnace in the summer, either. I track the daily temps, weather (rain/sun/snow/whatever), and when the furnace goes on and when I turn it off. I have had to run it to mid-June during the past three years.
This debate is nonsensical, wastes money that could be spent on developing better crop yields with less fertilizer, and does not about improving trash disposal by burning it to produce cheap electricity.
Why don’t we debate the issue of trash disposal? There are several manmade mountains of trash that are being mined now for methane, which is used to generate electricity for nearby communities. Recycling is a big deal around here: bring your unwanted electronics, metal stuff, etc., to the recycling drive. The area is cleaner than it was 50 years ago, by a long shot. So when is that kind of thing going to be recognized, and these idiotic panicky papers cease and desist?
This study is nothing more than the standard paul erlich – doomsday projection
It goes against the long term trend of ever increasing yields.
Skeptical science ran this same study a few weeks ago – with the typical justification ” it was peer reviewed”
In India Rice is grown in Summer, in Monsoon season and in Winter in which temperature vary by more than 10 oC. It is cultivated under high inputs under irrigation.
Dr. S. Jeevananda Reddy
I am a farmer in north Iowa, so I can tell you what is happening in the “real world of farming.” We have what we call trendline yields for all major crops. For corn and wheat the trendline yield is rising. In the real world of farming in our nation, the yields of these crops are slowly rising in a predictable and consistent manor. Is it possible that global warming is putting a drag on yields? Maybe, but all the other factors outweigh the “possible drag” meaning that it is not that big a factor. There is no current evidence that we need to worry about grain production in at least the near future or even in the long run. We are really good at producing grain in this country and can easily adapt to any changing conditions that might affect it. We humans are very creative in solving problems especially if we have the incentive (profit) to do it. We are not going to run out of food, unless we put the government in charge. Then I would worry.
Hi MikeB, – Think you’ll be interested in this late comment.
Maybe no more than 9% of the trend of greater yields for maize/corn in the last “… 50 years of increasing CO2 (73 ppm increase) …in dry conditions …” can be attributed to CO2; for soybeans CO2 bump good for possibly 12% of soy yield increase from 50 years ago (presumably related to legume nitrogen dynamic). The rest is related to various agronomic factors.
% for maize & soybeans stated above are from McGrath & Lobel’s “…combination of historical yield & climatic data & field experiments that do not require elevated CO2 …” extrapolations. Source is research titled (2011) ” An independent method of deriving the carbon dioxide fertilization effect in dry conditions using historical yield data from wet and dry years”
Google finds this abstract for McGrath & Lobel (2011):
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2011.02406.x/abstract
Full text here:
http://sci-hub.bz/10.1111/j.1365-2486.2011.02406.x
The authors note that F.A.C.E. (Free-Air CO2 Enrichment) experiments tend to show smaller carbon dioxide fertilization benefits than do container-based studies, and they guessed that the FACE experiments are better than the container experiments, and that the container experiments overestimate the benefits.
I doubt that is true. The problem with F.A.C.E. experiments is their unnaturally large fluctuations in CO2 levels. Bunce (2012) found that the FACE methodology results in an underestimate of the agricultural productivity improvement from higher CO2 level:
https://link.springer.com/article/10.1007/s11099-012-0041-7
It’s explained by Prof. George Hendrey here:
http://pages.citebite.com/d1r3n6l1c4vft
(or here: http://web.archive.org/web/20110717100621/http://www.qc.cuny.edu/Academics/Degrees/DMNS/sees/People/Pages/FacultyResearch.aspx?ItemID=26 )
I wrote at 6:24pm (currently in moderation), “The authors note that F.A.C.E. (Free-Air CO2 Enrichment) experiments tend to show smaller carbon dioxide fertilization benefits than do container-based studies, and they guessed that the FACE experiments are better… and that the container experiments overestimate the benefits… I doubt that is true. The problem with F.A.C.E. experiments is their unnaturally large fluctuations in CO2 levels. Bunce (2012) found that the FACE methodology results in an underestimate of the agricultural productivity improvement from higher CO2 level… It’s explained by Prof. George Hendrey here…”
Here’s an excerpt from Hendrey:
Hi Dave Burton, – The physical characteristics of plant containers is known to influence plant growth. This was identified as an issue for CO2 enrichment studies over 20 years ago (“Limitations to CO2 induced growth enhancement in pot studies”).
A good idea of issues surrounding container growing can be found in (2012) “The art of growing plants for experimental purposes: a practical guide for the plant biologist”; free full text = http://www.publish.csiro.au/fp/Fulltext/FP12028 . There is a brief subheading for CO2 itself & a notable statement was that “… At the beginning of an experiment, when plants are small, CO2 control is more challenging and necessitates some CO2 scrubbing of the air ….”
As for free air CO2 enrichment FACE tactical issues I find the following synopsis interesting & think container pot growth would be impractical for studying these environments. Quote below is regarding grasslands from (2006) “Plant CO2 responses: an issue of definition, time and resource supply”; free full text link = http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2006.01886.x/full
“Kansas. No response in wet years, significant gain in dry years, largely because of the responses of Cyperaceae and forbs. There was clearly no disadvantage of C4 grasses, most likely because they profited similarly from soil moisture savings as C3 taxa.
“Montana. The mean +40% response in biomass production was the result of one C3 grass species (Stipa comata) and was clearly driven by moisture savings, which permitted greater seedling establishment.
“Swiss lowland. No response in wet years, but a significant response in dry years, arriving at a mean +18% yield, largely because of Cyperaceae. The effect was almost completely explained by soil moisture effects of elevated CO2.
“Swiss alpine. Clearly no response, irrespective of season or nutrient addition. This site at 2500 m elevation has a dense, late successional heath operating under naturally low nutrition and at 25% reduced partial pressure of CO2. It came as a surprise that nutrient addition, which doubled biomass, did not facilitate a CO2 effect over 4 year.
“California. No overall CO2 effect, when tested across all combinations with warming, nutrient addition or watering treatments. When tested alone, CO2 enrichment exerted a 33% peak biomass increase. Surprisingly when CO2 was added to any of the other treatments, it reduced their stimulating effect drastically.
“Negev. The peak season biomass response was +17%, but resulted almost exclusively from the response of a single species out of 25 (one out of five legume species, Onobrychis crista-galli). Without Onobrychis, which is the most mesic element in this system, the CO2 effect was zero.
“Nevada. This desert system operates far from complete ground cover, and hence may expand. There was a small CO2 effect on a native, but a massive effect on an exotic Bromus ( ×2.3) because of the combination of density and individual growth (+50%) responses; forbs were stimulated by +40%. In shrubs, there was no response in relatively dry years but a massive effect in an exceptionally wet year (shoots extension c. ×2). Root responses to CO2 were negative (fewer roots).
Well I know my vegetable plants do worse when CO2 increases and the heat increases. Sarcasm. We need to pull federal funding from this nonsense.