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.
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There is an amazing array of information here contributed for free from a diverse set of commentators. My bottom-line take-away? The poor academics…with their constipated methods…ain’t got anyplace to hide. I almost feel sorry for them.
Pamela Gray? I love your little tale. Willis? You are a force of nature. I love this stuff.
Saw an article in the Minneapolis Star Tribune yesterday, aka The Red Star so it’s hardly a right wing organ.
It concerns the perfectly laudable effort by Episcoplains to send Mosquito nets to Africa to help save some of the 1 million or so people annually, mostly children, who die from Malaria there.
Their solution is nets, people get bitten and infected when they sleep indoors. But the size of the problem is actually a direct off shoot of the blanket ban on DDT which prohibits indoor as well as outdoor spraying. Which shows just how devastating the unchecked green movement can be.
But hey come to think of it a million here and a million there and pretty soon you’re talking real people aren’t you ?
http://www.startribune.com/lifestyle/faith/117910349.html
Hi Keith and yes what you say is true as I am an ex-Rhodesian myself.
What I find amusing is that the location of the crop trials are mostly in inhospitable and unsuitable cropping areas or areas where record keeping is certainly unreliable at best. Zimbabwe in particular is a very strange choice for the bulk of the tests because of the problems outlined in Keith’s post, the scarcity of fertilizer, suitable seed and the collapse of the irrigation systems/organised farming.
Using Google Earth to peek at some of the marked areas is useful including the maize hydroponics establishment in the middle of Lake Victoria.
Its bad to be wrong but it evidently won’t stop grant money.
They could learn a lot talking to successful farmers. Who is it best to ask, if they wanted first hand knowledge about anything. Normally the people closest to what you wanted to know would be a good place to start. It seems like a good idea to have some up front first hand knowledge about the research before starting. A good place to start is with people who are successful and then talk to those who are not. Or the other way around, which ever is your style. You just might have a better idea of what to look for in the research and avoid as much as possible mistakes. And it is still bad to be wrong.
In drought conditions, there is research showing low level soil biota corn crops do badly in comparison to soils with a healthy thriving soil biota.
http://soildoctor.org/?p=310
I tried growing corn just outside of Seattle. It was a waste of time.
Managed to get 3 or 4 baby corns per plant.
90% humidity is good, 100% humidity(precipitation) is bad.
This “peer reviewed” study is the perfect example of the decline in climate science, or more accurately, the decline in science we’ve seen due to the corruption now evident in a large segment of the scientific community. Other factors that would cause a reduction in yields were totally ignored. All is to be sacrificed on the altar of global warming.
All of us see how easily this “study” was knocked down, and one wonders why someone….anyone, who reviewed this study prior to publication wouldn’t have seen the weakness of the data. My God, anyone with any common sense knowledge could see the problems that are rife in this study.
Truly, this is a sorry time for science, but especially science in the Western World, and it saddens me, but more importantly is dangerous. The vast majority of progress we have made in the Western World over the past 300 years can be attributed to science, and to see science so corrupted by crass ideology like global warming and all its spawn is to see firsthand the decline of civilization.
As an add-on to the above it would seem that many of the test areas are subsistence farming areas and some of them certainly very remote and unlikely to deliver any sort of consistent yield data accurately. The best and most intensively farmed areas, the maize triangle in South Africa is not represented at all. I grew up on a farm in that area (Ventersdorp) and my family has been farming maize there for over 100 years. Meticulous records are kept about seasons and yields, droughts and floods, weather and so on. Not only them but probably most of the thousands of other old established family farms as well. Where better to go and do some serious and meaningful research? Just have to ask really, the records are there because these farms are managed as serious businesses and everything is monitored.
But no, lets do this on the edge of deserts, mountainous areas and in the middle of protected nature reserves (check Google Earth). Areas where despots rule, access is difficult and the subsistence farmers use draught animals. Where fertilizer is scarce or unobtainable, records are sketchy or non existent and folk will tell you what you want to hear.
“Yes sir, it is the fault of the global warming sir, and we would like you to pay us lots of compensation money sir. Bah humbug.
Doug in Seattle says:
Who funded the study? From what I understand NSF requires that the conclusions for the study be part of the proposal.
Doug,
Please tell me you were being sarcastic and I just missed it.
Without being too detailed…
I’ve a MS in Agriculture. Soils were my study area. Many of the previous comments were spot on regarding at least the test plot presented in the photo at the beginning of the post. The highly oxidized, likely highly weathered, frangible, medium texture soil will have low cation exchange capacity (it just won’t hold many nutrients even when added). This is, unless it is treated with lime or gypsum and “green manure” crops are grown intensively to increase the organic content of the soil, the cyclical nature of the growing season that does not include a winter which halts the action of fungi and bacteria on reducing the dead organic matter to CO2 and H2O will result in a cronic poor soil conditions for food crop production. This is especially true of one such as corn which has a higher soil nutrient requirement than others more adapted to tropical soils such as manioc, casava, possibly sweet potatoes, and others. I’m struggling with this love affair with corn. If they really want to grow corn in these poor soils, why not add the ashes from all the dung cooking, bone meal (as there are plenty of large herbivores), put a fish about 6″ beneath each deeply planted seed, and pray for rain.
Labor intensive? Absolutely
Nutrients for the corn? Absolutely
Did these data just presented require a MS in Agriculture or PhD in Environmental something or other? Nope, I learned this from Granny – she learned it from generations of folks for whom schooling was a luxury unnecessary to farming and logging in SE Louisiana.
They were growing sustenance on highly weathered soils abused by cotton farming for generations. They knew the soils were poor, they learned what made things grow by observation, trial and error, etc. The weeds at the edges of the ash heap grew taller and greener. The patch of grass growing after the cow patty rotted away was taller and greener. The old ant mound finally settled back flat was growing taller and greener grass. So on and so forth, they applied observations to getting more collards, okra, peas, beans, tomatoes, potatoes, corn, curcurbids, etc. out of the ground and into their stomachs.
My next statements may raise some hackles, but I think they are important to ponder. Is the starvation in many third world countries not a product of “relief efforts”? Has the injection of free food (energy) and discouragement of subsistence lifestyles created a demon? Through the massive shipping of food into these historically sparse regions of the world we have encouraged population explosions that were not possible before. Would not the training and education of a native population of agronomists, engineers, and teachers been a better approach in retrospect? They could have learned how to use the local resources for their own people then passed the lessons learned to the next generations. This would have followed the model of Europe, the USA, Australia, and now many SE Asian countries. I do not disagree that we (“the west”) have created the monster and are now responsible for it, but is the lesson now learned or ignored? Can we correct the problem, or is the corruption of socialism and communism so entrenched as to be irreversible?
Willis, where do I start with this?
Averaging min/max and putting an artificial 30 C figure is irrelevant to corn yield from a physiological perspective. This study is similar to climate research where people with absolutely no knowledge background begin number crunching. GIGO. The intricacies of that average are what is important (as in humidity, elevation, local climate, grid smoothing, measurement siting, etc in global temp averages). This issue has been studied hundreds of times before, but perhaps not in Africa. For non-imaginative scientists in the “publish or perish” scenario, replicating this study in Africa was an easy fix.
Corn, being a C4 plant, fixes photosynthate in a routine fashion up to about 90 F. At about 93 F (variation is due to varieties), the chloroplasts “shut down” and the stomates close. In between those values is a somewhat inverse logarithmic decline.
During pollination, however, pollen function is inhibited at significantly lower temperatures, which is probably close to the 86 F number they picked as a descriptor. If temps above that occur during pollination, you will get unfilled ears. If you’ve ever purchased sweet corn with missing gaps within the ear or at the end, it is a response to unfertilized florets (and there is an interaction with water availability). Therefore, this study actually indicates that when temps are averaged, and that average is above ~86 F one of two possibilities has occurred;
1. The daytime high was greater than ~93F and carbohydrate synthesis was inhibited.
OR
2. The daytime high was above 86F AND the corn was at the pollination stage (silking).
(or both)
The additional data you displayed is in agreement with this interpretation. The southern TX corn is a short season corn. You can buy corn varieties with maturity dates anywhere from ~70 day to 120+day. This means that the time it takes from planting to black layer maturity is X days. The folks in south TX plant a short season corn so that plant pollination occurs during a period of the growing season when temps normally do not go above an absolute value (for that variety) that may cause sterility.
I should add that yields generally increase with longer growing season. So to pick a shorter season variety will necessarily limit yield in itself. The issue in question here is then, are the farmers in Africa adept in picking varieties that are appropriate to the environmental parameters encountered in a “normal” growing season. We don’t know. Certainly, ~.5C AGW has not affected yields directly, especially when the data shows that most of that temp increase has been shown to be mostly associated with warmer winter and shorter winters (later frost-free date). Obviously, the tendency for farmers to view the last season as “average” (similarly to climate scientists) precludes their decision to plant a longer season corn for increased yield potential, but possible susceptibility to hot days at the wrong time.
Thanks for bringing this up. I rarely get the opportunity to discuss something in my field. ;~P
I’m an info-geek and a former farm kid from the edge of the dark green belt in SW Ohio. I understand what it takes to grow corn. Summary: ‘All the above’.
The study really sux and I appreciate what Willis does but the real key is not in the math but a compilation of all the empirical perspectives in these comments.
The real kicker is in Zimbabwe’s history; even a midwest guy who read the news knows that Rhodesian farmers knew what they were doing, before the country was ruined by ‘democratic practices’.
Browsing the original paper it’s obvious its perspective pointed to a foregone conclusion.
Which is moot when the history of the region is ignored. What’s needed is for an old style agronomy prof to do the study.
To PRD , above.. Yay!
My next statements may raise some hackles, but I think they are important to ponder. Is the starvation in many third world countries not a product of “relief efforts”? Has the injection of free food (energy) and discouragement of subsistence lifestyles created a demon?
I once encountered a liberal thinker on some forum who declared free markets dont work and cited a three page essay about the typical victim third worlder in Haiti who could no longer grow corn because of nearly free US imports.
When I pointed out that US corn exports especially under US aid auspices were hardly free market, he had to fall back on the typical lib gibberish we all know so well.
I told him to vote for politicians who would end ALL subsidies of everything and of course THEN he pointed out the ‘poor farmer’ and ‘agribusiness’ influences.
Indeed.
And those progressives can still be tied in knots when you advocate against ‘big biz’ for a truly free market.
Tim Folkerts at March 14, 2011 at 8:17 pm,
Try and uyse a little common sense please. Go back to your first reference and note what counties used irrigation and which counties did not. Look at the difference in yields.
That is the key to growing corn. Having plenty of water available especially on hot days.
The soil is an important aspect of holding water so the corn does not dry out. With good soil and plenty of water, the corn loves hot temperatures.
Willis Eschenbach says:
“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.”
The African sites stretch from ~10 °N to ~30°S. The tropics are defined as from 23.4378°N to 23.4378°S. This includes most of the African sites (excluding South Africa) and excludes Texas. In the tropics you do not get the variation of insolation, day length, and seasons as you do in temperate zones; so how do you vary the growing season?
As a Phd student working on my Crop and Soil Science, I am just amazed at the amount of bad papers and science out there. It does not take much to satisfactorily debunk many claims of crop failure. This is why I never reference ‘climate’ articles… and never will so long as I am able.
Willis’ introduction includes:
“Their conclusion? When it gets above a certain temperature, maize growth quickly slows, and it’s worse when it’s dry.”
Taphonomic says:
March 15, 2011 at 9:00 am
“The African sites stretch from ~10 °N to ~30°S. The tropics are defined as from 23.4378°N to 23.4378°S. This includes most of the African sites (excluding South Africa) and excludes Texas. In the tropics you do not get the variation of insolation, day length, and seasons as you do in temperate zones; so how do you vary the growing season?”
Are you suggesting that their claim about temperature should be restricted to the tropics? Or maybe you are suggesting that their study should be extended to take account of differences between tropical and temperate zones?
Ric Werme says:
March 15, 2011 at 4:40 am
Dave Wendt says:
March 15, 2011 at 1:57 am
BTW, someone in another comment mentioned the old rule of thumb that corn needed to be “knee high by the Fourth of July” to insure a good crop. I’m afraid that has become obsolete. Nowadays it’s more like “head high by the Fourth of July”, unless you’re a hot prospect for a low post spot in the NBA.
I’ve never seen corn head high here in New Hampshire by the 4th. We’re lucky to get knee high. Not surprising given the latitude and the 14″ of snow on the ground (somewhere around 35 cm).
Though it was admittedly not entirely clear from the comment, my BTW was meant as an addendum to my previous comment about corn growing in S. Minnesota and Iowa. If you should find yourself driving through those areas of a late June and observe many corn fields struggling to make knee high, you might want to take a flier on some corn futures, betting on higher prices in the Fall. Of course, I wouldn’t use any money that you couldn’t afford to kiss goodbye, because old Mother Nature has had a long term relationship going with her boyfriend, a certain Mr. Murphy.
Dave Springer says:
March 15, 2011 at 4:46 am
Thanks, Dave, for reminding us that there are mechanical constraints that affect where corn is grown commercially as well as climate constraints. In some parts of the world these include things like roads, transportation facilities, and the like.
And thanks to everyone for the interesting comments. Like I said, I love studying and writing about the climate because of the amount I learn doing it. Last week I didn’t know anything about corn, now at least I know a few things. One step at a time …
w.
WeatherBell shows it’s rainy season, get your seed maize ready;
Malawi 78-76*, Namibia 70 -66*, Swaziland 73-71, Zambia 65-63*, Zimbabwe 65-63*, Kenya 67-66*, Tanzania 66-65*, Mozambique 81-80*. But up Niger way it’s still a delightful dry 84-76*, but they (and their neighbors) go for planting millet anyway.
E.M.Smith, that was a hoot, as we say here in Texas, I heared dat! I gave the same talkin to my girls boyfriends and they had a look of oh shit on thier faces, needless to say my girls have never had a problem with any man thinking they can do them harm!
Taphanomic, growing seasons are different in any part of the globe depending on weather,water resources, soil management! The scientist did not not use real farmers or agricutral science in the study, they just seemed to go to the farms take a few pictures, then go get the data from far off weather stations, and sit down and write. there is more to getting good crops than just planting and sit back and harvest and these scientist do not seem to have any idea, my suggestion to you is to go back and reread the comments espesicially the ones from farmers of corn and you will see just how BAD of a study this really is!
Willis,
I’m not sure your definition for GDD is correct. The formula I’m familiar with for calculating GDD is as follows. Note that temps above 86 degrees F do not impact the formula at all. It is assumed in the formula that temps above 86 F for max temps do not harm the corn but don’t help it either. So by the definition of GDD the only thing that affects yield would be higher min. temps at night.
The formula for calculating growing degree days is to add the daily high temperature (86°F maximum) and daily low temperature (50°F minimum), divide the result by 2 and then subtract 50. The answer represents the heat units for one day.
GDD = [(daily high + daily low) ÷ 2] – 50
Example 1:
83°F (daily high temp); 63°F (daily low temp) 83 (daily high) + 63 (daily low) = 146 146 ÷ 2 = 73 73 – 50 = 23 GDD
Example 2:
95°F (daily high temp); 70°F (daily low temp) Since the daily high temperature is greater than
86°F, 86°F will be used as the daily high temperature. 86 (daily high) + 70 (daily low) = 156 156 ÷ 2 = 78 78 – 50 = 28 GDD
Producers can use a thermometer that reads both maximum and minimum temperatures to calculate and record GDD for their crop.
Theo Goodwin says:
Are you suggesting that their claim about temperature should be restricted to the tropics?
The article states “Roughly 65% of present maize-growing areas in Africa would experience yield losses for 1 °C of warming under optimal rain-fed management”
While they don’t specify where this 65% is, I would interpret Figure 3d as indicating that that it is in the tropical regions.
Craigo says:
March 15, 2011 at 4:57 am
This is my constant issue with these kinds of articles. They assume that if adverse things occur, people won’t immediately change their actions and habits to counteract it and indeed, in some situations, take advantage of it. Warmer weather? Grow warmer weather crops, or grow the same crops earlier, or …
I read today that they’re working on developing salt-tolerant avocados. Avocados are pickier than humans about their water. I have no doubt it will be accomplished sooner or later. Thats what humans do, we’re not slaves to the weather such that we’ll sit and watch yields decline and not take action.
w.
Why did they bother to go to Africa for this study? I would imagine that one could go the Ag departments in any of the Midwest state universities and find studies relating corn yields to every conceivable variable.