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.
Willis, I am having a real problem associating DD’s as I know them as they seem to be described in the article. For the heating profession, a single day may have a DD of say 6. In this case it is the average below a baseline. So if in the paper cited above, using 30*C as the baseline, one day that averaged 40*C would be considered a 10 DD. If I read the bit of abstract correctly, they are stating that growth is 1% less, per DAY that goes above that days baseline. For as your example showed, it is not hard to get 100 or 300 or whatever DD’s in a growing season. but as the temp graph below the DD graph shows, only about 20 days were actually higher in DD.
phlogiston says:
March 14, 2011 at 7:45 pm
“Having a journal named “Nature Climate Change” – as if there were something unusual and noteworthy about climate not being static – will hang like an intellectual albatross around the neck of this once-proud journal of science.”
Next up: Nature Global Rotation.
This link to the article was in Taphonomic’s comment to Anthony Watts’ earlier post on the subject. There are many comments there claiming successful corn harvests in climates just this side of Hades. {grin}
The article uses historical studies, interpolated weather, and a model that includes “ε [which] is an error term.” The studies were conducted by a number of groups and seed companies, and they tested a variety of varieties of tropical maize [n.b. – not North American] “grown or intended for farmers’ fields throughout Africa.” Possibly under conditions different from those at the test site(s)?
In other words, it seems to me that verifying this article would/will take much digging, and I hoist my glass of ice tea to those who would take it on!
I just read the Wiki entry on Maize. Apparently EVERYBODY can grow corn quite well except for that area of Africa. In fact, folks with nothin but a mud pot figured out how to cross breed and domesticate the damned stuff to the point that it hasn’t changed much over the past 2000 years. The stalk has larger than grass leaves on it, the ear of corn grows on the side, and the tassle is on the top. All this was figured out wayyyy before climate Ph.D.’s were piled higher and deeper. Thousands of years before that, it was just a piss-ant grass.
So, if folks down there can’t grow corn, something other than global warming is the cause.
Perhaps there is something amiss with the interpretation of “Each degree day spent above 30° C [86°F] “. Perhaps they are referring to, in effect, the total “cooling” degree days for the growing season offset by the “heating” degree days. That would take into account the days of cooler weather early or late in the season. In the example shown for Edinburgh, TX, the result would be a negative number, indicating that temperature did not have a negative influence on crop yield. It does not make sense, for example, that one really hot day could have a serious negative impact on yield if all the other days were optimal temperature. Also, wouldn’t the timing of the hot days also matter. A hot day early in the season likely would cause more reduction that a hot day on the day of harvest.
If the study was a simplistic as it sounds, it was simply a waste of time for everyone as no meaningful information resulted, except of course to fuel climate lunacy.
In the blog, I read the original Nature peice – Gosh!
Next, I read Willis’s observations – Ungosh!
And all sorts of questions, which must be answered urgently, arise in the mind of this (ex) relatively uneducated bureacrat, now hypothetically charged with the duty of making financially significant decisions on all sorts of subjects about which I know next to nothing:
(1) Who is right? (Must be the original article – after all it was in a respected publication. )
(2) Why does Willis not publish a comment or something in Nature? Who is he, anyway? Do people with power/influence agree with him?
(3) What do I tell my minister, who takes decisions on on all sorts of matters he knows nothing about as a matter of routine, on the related question of subsidies to windmills?
Enough!
It will take more than blogs to bring the body politic to its senses. Friends have got to be made in the right places. And then what sort of contortions are we going to have to come up with to preserve the dignity of our politicians, who, after all, only did what we told them?
And I do like Willis’s writing, although, in my experience in places similar to that of which he writes, the winds blow into an appraching storm, not out. Have his efforts been assembled into a book somewhere?
Obviously corn is not a major crop in Mexico.
Remember the remark, “the scandal in Washington isn’t what’s illegal but what’s legal”? What’s scandalous here isn’t this flawed (// “illegal”) paper, but that it passed peer review (// “legal”).
Growth is less when it’s warmer? Might this affect some tree ring studies?
Ken Stewart says:
March 14, 2011 at 6:54 pm
Ken, remember this is average daily temperature (max + min)/2, not maximum temperature. Run the Wolfram Alpha calculator for a town in the growing region.
w.
PS: I.e., the reviewers should have brought up the objections that have been brought up here and in the earlier thread on this paper. Why didn’t they? Because that would have hurt the cause, because they would have been criticized by more extreme alarmists for their stance, and/or because they believe that “any stick will do to beat the devil.”
Herbie says:
March 14, 2011 at 7:17 pm
Possible, but I don’t read it that way. It would be difficult for the L2011 folks to calculate if that were the case. I read it as a linear trend. Makes no difference to the conclusion either way, though.
w.
Using 30°C as an upper bound is just wrong. Sweet corn (maize) likes it hot, and grows best between 85°F and 100°F, or 30°C to 38°C. Above that range (and below it) maize doesn’t do as well, but some varieties of maize have been grown in equatorial South America for thousands of years. Maize pollen has been found in terra preta (Amazon dark earths).
This book is a good read on corn agriculture in Africa:
“Maize and Grace: Africa’s Encounter with a New World Crop”
http://www.amazon.com/Maize-Grace-Africas-Encounter-1500-2000/dp/0674025571/ref=sr_1_1?ie=UTF8&s=books&qid=1300166132&sr=1-1
I agreed with Anthony’s previous post, that the Eurekalert description of the study was crap.
I managed to find the published report on line and posted a link to it in a previous post without a “subscription”.
With all due respect, Willis, I think you’re being harsh on the authors of this paper.
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.
Maybe they shouldn’t have linked the potential results to possible global warming. But given the contributions that Norman Borlaug and CIMMYT have made to civilization, I find it difficult to fault them for this paper. Without Borlaug and CIMMYT we would probably have worldwide starvation. Don’t believe me? Fine.
Google Norman Borlaug. He’s someone that most people have never heard of but has impacted humanity incredibly, and who deserved his Nobel prize
I suspect you’ll find that map corresponds more to where the tall grass prairie used to be. It is likely a matter of soils, as well as summer climate during the relatively short growing season.
Corn/maize was genetically-modified from the grass teosinte by the Maya and developed by other native peoples in north and south America for thousands of years. It is a tropical grass, and grows in tropical conditions. Iowa in the summer is tropical, thanks in part to the corn which generates its own microclimate in those conditions.
You listen to the farmers when it takes down global warming, but commentators ignore, insult or accuse them when it comes to ground-truthing ethanol production, crop prices, the very nature of agriculture, or the wind turbines on the horizon.
That is not a sign of the sort of truth-seeking one would desire in a site such as this.
Actually, I think the corn is smarter than the L2011 climate scientists
Having spent many years living in Swaziland I can contribute the following about maize production there:
Maize yield is highly dependent on 1) the seed variety chosen, often a hybrid of recent regional development, carefully selected with professional advice; 2) the planting density per ha which is a guesstimate on the coming rainfall (which varies in a sine wave fashion over a 19 year period, presently very wet); 3) the timing of the first rains and the development of weeds by the time schools close (‘weeds’, many of which are edible have a very large effect on yield); 4) the relative proximity of school closing for the year: if planting is late, it may be at 3-leaf stage when weeding (hoeing) starts after kids get out of school. In that case yields will be highest. If the planting is early and it is well past the 3-leaf stage when schools close and weeding starts, yields plummet.
Heat? It’s Africa man, nearly as hot as Atlanta in July! Well, almost…
Most vegetables stop growing between 10h00-16h00 when the temperture goes over a threshhold. That is why shade cloth promotes growth all day.
Short season maize is grown in the Kalahari Desert and the southern Swazi lowveld on dry land: very dry, very hot. According to the Malkerns Research Station’s experts, the easiest way to increase yields of maize is to plant early and move the end of the school year forward.
The paper’s underlying bedrock? From here it looks like statistics, all the way down.
juanslayton says:
March 14, 2011 at 7:47 pm
It’s from here (PDF). Per google earth, it’s likely some of the center-pivot watered stuff north of Pearce and around Elfrida.
w.
“I’ve never known corn to bolt. But other types of cool weather plants bolt like crazy in warm weather. ”
This study finds that plants have a temperature gene and will respond to high temperatures to protect the next generation of seed.
http://ec.europa.eu/research/headlines/news/article_10_01_21_en.html
In a nutshell, the real scandal isn’t that this paper got written, it’s that it got published.
“There isn’t a source of fertiliser in Kenya, the cattle dung is used for fuel to cook over, the forests near any reasonable village have long gone, trying to change farming practises can be and is, a lesson in futility unless you are prepared to spend time living alongside the people.”
Too bad they don’t have some low cost coal for their fires. That would have saved the forest and allowed them to use the dung as fertilizer. No hope of that in the future once the UN and IPCC get done with them.
The Economist issue of February 26th 2011 has a series of articles “A special report on feeding the world” which might be of related interest if you can ignore the AGW will make it worse slant.
http://www.economist.com/printedition/index.cfm?d=20110226
I can tell you that there’s some corn farming here around the Phoenix area, probably not enough to be counted on the map. I have watched some farms get 2 crops in a year out. I’m not sure when they plant, but they’ll be harvesting in July, and then another crop will be sprouting up and gets harvested probably in October (temperature is still in the upper 90s in October).
Lots of people referring to wiki in here.