Guest Post by Willis Eschenbach
Anthony has discussed a paywalled study in the new reality-based Nature Magazine production, Nature Climate Change magazine. Unlike Anthony, they approved my application for a free subscription … go figure. The study is called “Nonlinear heat effects on African maize (corn) as evidenced by historical yield trials”, Lobell et al. (hereinafter L2011). The study looked at the effect of heat on corn production. Here’s their Figure 1:
Figure 1. The opening figure in the L2011 study of maize production in southern Africa. I always enjoy rich visual presentation of data, note that this contains elevation information as well.
Their conclusion? When it gets above a certain temperature, maize growth quickly slows, and it’s worse when it’s dry. Of course with the obligatory links to global warming and the danger of large drops in corn production. Shocking news, I know. They provided a citation to other scientists saying the same thing, in case you doubted it — too much heat is bad for plants. I bet the farmers of the world were as amazed as I was.
Or as they put it in their abstract:
Each degree day spent above 30° C [86°F] reduced the final yield by 1% under optimal rain-fed conditions, and by 1.7% under drought conditions. These results are consistent with studies of temperate maize germplasm in other regions, and indicate the key role of moisture in maize’s ability to cope with heat.
Now, we need to be careful here. They are not talking about the number of days where the temperature goes above 30°C. They are discussing “degree days”. That is the sum of the average daily temperature (C) less 30 degrees, for all the days where the average temperature [defined as (daily max + min)/2] is above 30°C. The figure is written as “GDD30+”, for “growing season degree days over 30°C”. They figure the growing season as 150 days, which agrees with the Texas figures given below.
Are their numbers accurate? Is there a drop in yield of 1% for every degree day as they claim? I don’t know. Haven’t done my homework yet, just dug up the paper, gimme a minute. Where do they grow corn? Iowa? Let me look it up. OK, I find:
Figure 2. Major (dark green) and minor (light green) corn growing areas in the US, by county. Texas is the large state numbered “2”. Between 60-70% of Texas corn is irrigated.
Fascinating. I love doing this, I get to learn so much. Well, at first glance I’d say the following:
1. The major corn-growing areas are from about 37°N to 47°N. So clearly, corn prefers temperate weather.
2. Corn is only a minor crop in many regions within that general preferred temperature band. So obviously, there’s other factors. The usual suspect would be water, second would be soil.
3. Corn is grown in the California Central Valley, one county in Arizona (irrigated, no doubt), a number of counties in southern Texas (mostly irrigated), and one county in Florida. I looked at the temperature record for Hidalgo County, the left one of the counties at the south tip of Texas in Figure 2. I looked at the daily temperature record for Edinburgh, in the middle of the county.
Here’s the curious thing. During the corn-growing season of 1999, the total number of “degree day[s] spent above 30° C” (GDD30+) in the Texas corn-growing area was 136 … so if yield dropped by 1% for each degree-day over 30°C, we’re down below zero to a quarter of the original yield. Hmmm. Figure 3 shows the degree day analysis, from the excellent online calculator from Wolfram Alpha here:
Figure 3. Degree days over 30°C for 150-day 1999 corn-growing season, Edinburgh, Texas.
I got to thinking about what was happening. How could they be growing corn in that kind of heat, with a GDD30+ over a hundred and thirty? I thought about it a while, and looked around on the web a bit. Figure 4 shows part of the answer:
Figure 4. Corn planting and harvesting dates in Texas. The “Panhandle” is the most northerly square section of the state (see Figure 2). SOURCE.
I’m sure you see the pattern. In the south, like Hidalgo County above, they plant and harvest early. Their crop is three-quarters harvested before the rest of the state has even begun.
As for the other part of the answer, I don’t know. I don’t know why even with their early growing season (March 1 – August 1) the Texas farmers are still able to grow corn in that heat. The L2011 study says that’s impossible, but perhaps the Texas guys and gals didn’t get the memo, they’re a cactus-tough bunch down there, hard to get hold of. Thinking on it, though, it’s more likely they got the memo and shot it full of holes for target practice. In any case, during their growing season, the Texas farmers have no less than a hundred and thirty-six degree days over 30°C, which according to the L2011 results should reduce yield by 136% 75% … which means that either I or Wolfram or the climate scientists did something wrong. I’m open to any suggestions, I’ve been wrong before.
Now, if there were to be a general warming, say a degree on average over some long time, what do you think will happen to the planting and harvesting dates in Figure 4? Do you think those farmers would keep planting at the same time of year, year after year, in the face of increasing hot days summer and decreasing yield? Do we really face a 1% drop in yield for every degree day over 30°C?
Naw … in answer to the question in the title of this post, farmers are smarter than the L2011 climate scientists. If temperatures change, the farmers change their planting times … what do you do?
My best to everyone.
w.
Dear Willis,
Your question, “which group is smarter”, brings up clearly the problem with the present generation of “scientists”. It has become too easy to become a “scientist”. It is still very hard to make a profit as a farmer.
The question should be: “which group works the hardest” .
In a blog of questions and answers in physics, a young fellow asked : What are the easiest fields in physics to work on? Not so easy that they have been solved centuries ago or elementary textbook stuff. Something you can actually work on, but easy enough to take minimal effort.
Note the “minimal effort”. It is the science aspect of the “me” generations we have managed to bring forth to the world: the maximum gain for the minimum input of effort.
Thirty years ago, I had been shocked when giving a lecture to prospective graduate student applicants one of them asked : “what is the career path and what type of pension will we get?”. I was shocked because my generation of physicists, just coming out of the hardships of WWII and a civil war were happy to be able to play and discover in physics, and did not give a dime about “job security” at that age. This fellow got his PhD and has been a very hard worker.
Counting 15 years for a generation, two generations later we get this minimal approach, the Spock generation of permissive up bringing? In combination with the needs of academia to grow and create tenure posts, levels of examinations have dropped and the science system is being filled with minimal effort candidates for study, who should have been rejected at the word go. Minimal effort does not give large grades.
So enviromentalism and stuff are the right place for these minimal effort fellows and according to ” work expands to fill the time available” , “nonsense expands to fill the journals available”. Journals make a living too.
Sadly.
Maybe the Dingo at their corn?
Mexico grows corn in winter…
http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=49652&src=eorss-nh
I see that many samples were taken in Zimbabwe. Remember that when it was called Rhodesia, it was referred to as the breadbasket of Africa. I guess the political situation, murder of farmers and theft of farms hasn’t affected the results of the tests here?
Based on IPCC “greenhouse” scenarios, tropics should not warm but mid to high latitudes should. So all that screaming about Africa is off.
Tim Folkerts says:
March 14, 2011 at 8:17 pm
Thanks, Tim. However, the temperature during the growing season is similar across Texas (due to the delayed planting and harvesting). So production should be down all across Texas.
In addition, here’s a study of field trials of corn in Hidalgo County, Texas. It gives average yields of 160 bushels/acre, with some hybrids giving 180. Texas-wide average is lower, at about 120 bushels/hectare.
So even with all of the adjustments, the numbers still don’t work. Texas yields on average are three-quarters of the Iowa yields. In addition, the Iowa farmlands are much richer, deep topsoil.
w.
PS – I finally unravelled the actual relationship they discuss. They say that the natural log of the yield is linear with the GDD30+. So yes, the yield should be down to a quarter of the original yield … still doesn’t make the numbers work, though.
From being an organic gardener in Kansas I find the best tasting and most drought resistant growth comes out of soil with loose texture and lots of organic matter, the absorption rate of water out of the soil, is the make or break criteria for dry land farmers. The finer and clay like the soil with less organic matter content the corn is grown in, determines that it is the first to dry up and die when it get windy and dry.
You can drive through the country and look at the condition of the corn crop in drought periods. Most of the local farmers keep an eye out for the fields that consistently survive, when planning more land purchases. Milo is the back up crop for dry areas and years, still pig and cattle feed.
The dirt in the photo from the article Anthony links to, probably wouldn’t grow decent grass for pasture, until a decent sod was established.
So, do people actually get paid for writing a report that can be demolished in one fell swoop by a few google searches? OK, W has a brain which for sure is by far larger than mine, and he also makes demolishing the report look so easy.
One question: Can we have our money back please?
Next question: How many ‘scientists’ have been paid and are being paid for producing ‘peer’ reviewed ‘scientific’ reports that can be ‘Eschenbached’ in a few minutes?
Taphonomic says:
March 14, 2011 at 9:22 pm
Southern Texas is at 26 North. The bulk of the study sites are around 20 South. Neither one strikes me as particularly tropical. And yes, it gets damn cold at night in southern Africa.
w.
The biggest problem with high temperatures and growing corn are when the peak temperatures occur during pollination. This is about a 3 to 5 day period and high temperatures will cause low kernal count on the ear. Growers mitigate this by planting the correct hybred early enough that pollination occurs before the peak summer temperatures. If there is adaquate moisture (in the ground) corn loves the heat.
Taphonomic says:
“Somehow I find these discussions of similarities of growing corn in temperate (non-tropical) regions with equatorial (tropical) Africa a bit disingenuous. Why? Because it doesn’t really get cold at night in Africa like it does in Texas or Illinois. You don’t get seasons in Africa like you do in Texas or Illinois. They are discussing agriculture in an entirely different climatic regime; one that is not a prime location for corn growth. ”
Actually nearly all the growing sites in Africa are in highland areas where nights are fairly cool. The sites in Lesotho for example are in an area with regular frost in winter.
[Snip . . Off topic . . ]
The soil in African is rich in Laterites: iron and aluminum oxides. As shown here:
http://www.britannica.com/facts/5/418439/laterite-as-discussed-in-Africa
Which is why the soil is red/brown. Aluminum stunts the growth of plant roots, which is why Monsanto is creating a GMO variety of corn that is Aluminum resistant.
Maize is not native to Africa, which has a highly acidic soil, hence the presence of Laterite.
http://pcp.oxfordjournals.org/content/36/1/201.full.pdf
http://www.ehow.com/info_8034957_aluminum-toxicity-soil-acidity.html
I don’t understand why these “temperature”researchers can’t do just a bit of homework. The temperature, of course, has everything to do with why tropical jungles are so desolate….oh, wait…jk
And on the other hand, if global temperatures were to rise and, as it is reported, it were to warm more nearer to the poles and less nearer to the tropics, would there a net overall greater or lesser opportunity for good farmers to increase global corn yields and yields of other crops? As surely some significant areas are currently too cold to produce corn economically.
When I plant seeds for my garden I look at what the weather is and has been doing so I know if it worth while doing it or should I delay.
James Bull.
I agree Willis. In the lowveld, Swaziland (one of the study countries) reaches -4 at night. Much colder than the higher areas like Manzini, strangely enough, where it never gets a frost. Swaziland is at 26 South. Same as Texas.[shome mishtake shurely]
Glad you got the math right. 1% drop from the last value. The 1% is clearly untrue save perhaps for a small numbers of days and that is likely to be highly dependent on the seed variety. Humidity will also play a major role. I expect the real relationship to be related to the humidex, not the temperature, and to be limited in range.
Just to the south of Swaziland in the KwaZulu-Natal highlands the farmers have ‘ton clubs’. The ten ton club has members who have cropped 10 tons per hectare. There is a 12 ton club and so on. There is no economic return above 8 – they just do it for fun.
Ox-drawn commercial farmers in Swaziland (yes, they exist) get about 3 t/ha and ‘rented tractor’ ones get about 4.2 t/ha. Those are old figures. They reflect ‘peasant farming’ with hybrids and fertiliser. Rain appears to me far more important than temperature: i.e. check for timely rains, not +30 days, especially around tasseling.
And further – about 50% of all the food grown in Africa is eaten by pests. Think about how easy it would be to offset cold or heat or drought of flood-related losses with well known control measures.
Did anyone do a study on the effects of cold on yields?
Perhaps this wouldn’t get published by Nature.
Jeff Alberts says:
2. Corn is only a minor crop in many regions within that general preferred temperature band. So obviously, there’s other factors.
For those who speak English, that would be “there are other factors”. 😉
Well, to quote my Texas Uncle:
“Well, son, we won’t go holten that ‘gainst yah. There’s been lotsa facturs ’roundt hearsabouts, and spiiken Anglish aint won we been known for holten ‘gainst a fella.”
Soes if yous ‘ill just stop t’ holler ‘n about it, we ken prolly get you’all ‘t pass with’n out too much trouble….
‘Corse, if you’all are gonna make a fuss ’bout it, well, let me introodoose you to some Texas “Culturall Art E Facts”… This ‘un here, it’s calt a “Three Fifty Sev’n Magnum” and this other ‘un, it’s calt a “Foorty Five Colt”…
😉
I “married in” to a Texas Family. It has been ‘interesting’….
They would do ANYTHING for me and my wife. On the other hand, in the “meet and greet” of the family my Texas Uncle said “Howdy. I want to welcomes you to tha familly. And just soes you know, if you EVAH do ANYTHIN to hurt this lttle girl, I’m gonna personally hunt you down and kill you.” Delivered with a sincere smile… Now, I grew up in a ‘western town’ so I was not totally unprepared… but he WAS a guard at a state prison …. and always traveled armed… I said: “Aint nobody evah gonna hurt my wife. But thank you for your concern” or something close. Basically, the other side of The Deal “She’s mine, and I’ll die before I let someone hurt her; but if you are near it’s nice to know you will help with the shooting”.
The simple fact is that he was NOT kidding. This is the “code of the west”, and I knew it. It was his Honor Duty to inform me that he was “on the job”. Just as it was my duty to inform him that anyone who so much as touched a hair on my new wife was going to be skinned, but I was not sure if I ought to do it before, or after, he was departed from this world…. so could he help me out with that bit of stupidity on my part and ‘splain it to me…
Now, the hard bit for folks “not of the ken” to get: I’m well above average IQ, and so is he. There is a tendency to attribute to intelect that which is best assigned to cultural norms…. Well, “It ain’t that…”
The point?
I’d suggest, just a tiny little thing, that maybe you ‘oughten not t’ be crisizisin a cowboy ’bout how’s he’s speakin’… ’cause … well… I’m married to a Texas Gal an he’s a cowboy an well, there’s this here “Code Of The West” an it can be bit tricky for you’all folks from Angland t’cotton to it an all… and I’d really rather not have to ….
Willis, another beaut! I spent a number of my early years after leaving high school working on and near agricultural and horticultural research stations of various sizes. A weather station, no matter how basic, was always part of every station. Most agronomists know that weather is incredibly local and doing nifty staistical extrapawhosis never provides real and useable data; without factual weather data the research is pointless. The soils and the nutrients that crops are grown in are important too, but any real study of the this seem largely absent in this paper. I fail to see any real point of the paper; the agronomists I knew all those years ago, who were generally weatherbeaten from actual outdoor observational work, would be horrified that scientific study in their feild can be largely carried out in a comfortable office sitting in front of a computer.
Richard
March 14 2911 08.04
You Sir have hit the proverbial nail,
Having been born into a corn growing family, and also traveled,’there and back in Africa’
Corn is a fantastic plant, the seeds are set in the cob the in same direction as they form on the stem, you will find that in a field of corn that the best yield is always in the outside of the field, this is because it gets more sunlight, and if the seeds are planted in the right direction so as the cob is on the outside of the row the yield will be greater all over the crop
Good post, certainly if Framers were not smarter than some scientists then we would be very hungry.
Keep em coming!
I’m late of course, but did someone spend a lot os hard-pressed taxpayers’ dosh on arriving at a conclusion that farmers, as wonderful as they are, complain that it’s too hot??? I thought they complained because it was too hot/cold/wet/dry/wrong type of rain/wrong kind of heat/wrong kind of cold, for too long, etc, basically everything & anything! I blame all that nuclear testing in the 40s & 50s that’s caused all that evil CO2 to be emitted causing catastrophic global warming/cooling/no difference/slight difference/possibly some difference but we can’t be sure difference……..I quit! Watch out for the anti-nukes surge in the coming weeks & months. Sarc off. :-~)
etudiant says: Excellent post. […] That said, one wonders whether the Texas farmers are getting yields comparable to those in Iowa. That might give some better sense of corns higher temperature sensitivity.
all this is on line from ag schools and ag extensions. You vary the variety or the planting date as needed. This is just “below basic” stuff. Corn cuts off at 50 F low and grows best at 86 F so above that is pretty much static high (remembr it’s only peak for a few minutes a day…)
See:
http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/a834w.htm
Corn is currently grown in every county in the state, though the productivity and risk of production varies considerably from region to region. Temperature, rainfall and radiation are the major environmental factors that influence the growth and yield of corn.
Yes, “radiation”. Did they measure that?…
It’s a temperate crop. So if it get too hot, they will swap to soya beans… FWIW near the part of Texas where I spend “some time” they also grow sorghum, but only in those places where they have some issue with corn. The point? You change horses when the one that can’t take the heat keels over…
More warm and longer warm is better. I think some academic screwed the pooch…
There are many ways to calculate heat units. Usually the upper and lower bounds are set by the particular plant of interest. This says corn needs AT LEAST 50 F but tops out at 86 F (though will grow hotter, does not get more gain). So for every place that rises above 86, somewhere else rises above 50 F…
So it’s well established that 86 is the top growth rate (over about 120 F you need to ‘go negative’ on the factor instead of just pegging at high growth) and that’s just not a problem, really. As long as you REACH 86 F you can reach max growth…
So how much of the planet is below 86 F and could use a bit more warmth?…
Richard says:
March 14, 2011 at 8.04pm
‘I would suspect (without any evidence) that this study shows more about the effect of political megalomania than temperature.’
Sounds like climate science and agw in general, more about political megalomania than temperature.
I was born in a small SE Minnesota town right on the edge of the dark green portion of the corn map and have spent most of my over six decades of life here. My wife of nearly three decades was born in S. Central Iowa and her mother still lives there. As a consequence I have spent good deal of time over the last thirty years driving the back roads through some of the most productive corn growing areas on the planet. It is entirely usual for corn fields to have completely different results when the only thing that separated them was the road I was driving, or sometimes a fence row, or even in fields planted by the same farmer based on drainage differences. It is commonplace to see test plots planted with several rows each of a large number of different seed varieties where the variable results are obvious even from a passing car. Corn yields are the product of a wide assortment of variables. Even if they had a recording thermometer attached to every other cornstalk it would only enable them to suggest a possible correlation between temperatures and corn yields, unless all the other variables were adequately accounted for. Trying to claim a causal relationship based on temps interpolated across vast distances with almost no data on the other conditions affecting yield is just laughable.
Pitstops tend to be fairly widely spaced across central Iowa, so I’ve had the opportunity to venture into cornfields to conduct personal drainage checks on quite a few occasions. I couldn’t unequivocally deny that high temps might decrease yield, but I can report that on +90F days with little breeze, if you stand fairly still in an Iowa corn field you can actually hear the stuff growing.