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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EM: Great contributions.
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 your a hot prospect for a low post spot in the NBA.
My family farmed maize, cattle and sheep in the Free State Region of South Africa from around 1860 – 1930, one of the regions selected for the paper under discussion. The area is typical ‘steppe’ country, rising to mountains in the East (The Malutis and the Drakensberg) which intercepts any potential rainfall coming from the Indian Ocean. The Free State Plateau is 4,000 feet above sea level on average, rising to around 5,000 feet in the East and the foothills of the Malutis. It’s pretty dry country folks and the soil, though good, cannot give the sorts of yields enjoyed in countries like the US, Canada or the European and Russian equivalent areas.
Having lived there myself I can say that most of the summer is hot, typically above 30°C and most of the rain is from thunder storms that sweep across from the Atlantic side of the continent. Winter snow on the Maultis and the Drakensberg provides most of the feed water for the major rivers round there.
Why did my family cease farming? We were finally wiped out by the South African equivalent of the 1930’s ‘Dust Bowl’ years. the drought lasted a good five years in the Eastern Free State and destroyed crops and grazing. Entire herds of cattle died being moved in the hope of finding water near the coasts – some 200 – 300 miles at the minimum. No rain for about five years followed on from an infestation of ‘Rinderpest’ a disease carried by wild animals, but fatal to domestic stock. It bankrupted most farmers, including my Great Grandparents, and drove them off the land. This sort of heat and drought is very much a cycle there, probably operating on around a 100 year switch round.
Yes, heat in these areas affects growth – but the lack of water when it gets very hot affects it even more. The mines have been pumping out the ground water for a century or more and the water table has dropped by something of the order of 1,000 feet. The desert to the west, the Kalahari, is encroaching by about 20 miles a year at present, though the closure of some of the deep mines may allow the water table to recover.
To me this paper is a classic case of Expectation Bias and Tunnel Vision. Crops reducing? Must be Global Warming. What d’ya mean there are other factors?
Willis,
The more likely suspect in Africa is poor growing practices.
I also believe that African countries, if I recall correctly, have rejected GM crops that are designed to withstand heat, among other things, better.
By the way, 1% day per yield reduction results in an asymptotic function., not a linear drop.
Willis, I would bet the difference in Texas yields is RH%. I grew up in Indiana. We had corn everywhere, used to eat feed corn right off the stalk, uncooked. But my observation is that it loves humidity. If one shifts the growing season in lower latitudes, the shorter LOD will produce lower yields than the standard season in higher latitudes, with nutrient and water being equal.
Dave Wendt says:
March 15, 2011 at 1:57 am
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).
Of course, the map Willis included says we don’t have corn here, so perhaps that crop that grows in floodplains where it’s flat enough for tractors isn’t really corn. Sure is good though come August and September. Looks like grass. Maybe it’s bamboo.
Then again, up heah our best known crop is rocks – we don’t call ourselves the Granite State fer nuttin’. We’re so desperate for crops we boil down tree sap and put it on hotcakes. (Which global warming says we won’t be doing in the future. Some friends were up most of the night boiling down 1,000 gallons a couple days ago.)
As for that graph on which we’re abusing “the limits to growth,” Willis said it was really linear with the log of GDD30+. I was going to suggest the yield curve likely starts out flat, steepens and then tails off as the last areas to give have more than average water and shade. They wouldn’t do well, but do better than a brown corn stalk sticking out from dust.
“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.”
Water and soil aren’t generally chronic problems in the corn belt. Terrain is likely the biggest determinant outside climate. Cornfields are usually on vast flatlands. Other crops with higher value/acre can be economically cultivated on terraced land but commodity staple crops that rely on being able to pull big wide attachments behind a tractor can’t compete when grown on more challenging terrain.
One thing is for sure from the map… corn grows best in temperate climates with reliable but not excessive rainfall. I see it growing in South Central Texas but it usually doesn’t look as good as it did where I grew up in Western New York State. When I lived in Southern California usually the only place you saw it was in hobby gardens not farm scale production. In SoCal you couldn’t swing a dead cat without hitting an orange grove, avocado grove, or strawberry field.
The study period almost exactly matches the politically inspired economic decline in Zimbabwe that started in late 1998 culminating in the progressive eviction of 90% of commercial farmers from their farms. The hyper inflation that followed impacted through the economy affecting power generation (essential for irrigation), fertilizer production and distribution, availability of foreign exchange vital for spare parts and all the extension programs and crop development activities that were sustained by productive farms and seed development programs.
Compare and contrast with Zambia that is recording record harvests and productivity levels. http://hken.ibtimes.com/articles/113728/20110217/zambia-2011-maize-output-seen-beyond-2-8-mln-t.htm through improved extension and farmer education services (and a few ex-Zimbabwean farmers). Amazing what can be achieved despite the alleged impact of climate change.
Further to that it is obvious that the Zimbabwe corn/maize crop is totally dependent on rainfall. This season started out well but there was ( another ) prolonged mid-season dry spell that has ruined the crop in the Masvingo, Manicaland and Midlands provinces.
This is because of the destruction of irrigation schemes by untrained farmers and others who simply cannibalized the existing infrastructure for sale as scrap because something given for free has no value. The primary reason for that statement is that the land is not owned by the farmer. He has no legally defensible title as he is there on a “grace and favor” basis by government. This means that the farmer is unable to raise loans against the land as it has no sale value. He cannot pledge, sell or bequeath the farm.
It is true that high temperatures cause wilting in Zimbabwe because the high temperatures come about because of the absence of rain , think cloud cover. Irrigated maize is highly productive and yields of 10 t/Ha are not uncommon on those farms that irrigate. Whilst hybrid seeds are used in Zimbabwe GM seeds are banned and as was mentioned there are severe constraints on the supply of fertilizer because of massive contractions in the economy.
Zimbabwe needs about 2m tonnes of Maize a year to meet domestic demand. This has not been achieved in the 10 years of the land revolution and has been on several occasions less than 1m tonnes. The crop is almost totally at the whim of the rainfall and despite there being several technologies available to limit this dependency they are not applied because of lack of capital ( valueless land ) and government policy on land allocation and GM crops.
My grandma had an Indian woman from the Nez Perce tribe for a nanny when she was young. That woman could grow just about anything under any conditions. It was from her that Grandma learned about the corn hill. At the bottom of each hole in the dirt mound (IE hill), she placed a fish, covered the fish with a bit of soil, then planted the corn. Pole bean seed was interspersed with the corn seed, and squash was planted on the outside edge of the group of corn and bean seeds. The only other thing we did after that was remove suckers from around the hill of corn shoots so that only 3 or maybe 4 stalks grow in each hill. The soil nutrients were helped by the bean plants and the squash plants kept the soil cool, moist, and free of weeds.
One year she decided to put chicken droppings instead of fish in each hill. Ever watch that move, “Little Shop of Horrors”? We still don’t, to this day, know what that crop was, but we stayed out of the garden at night.
Another half arsed paper to bolster the ‘consensus’ in the next IPCC report.. Thanks for the analysis Willis! I get the feeling you’ve only hit the tip of the iceberg with the inconsistency and data mangling used to trot out the same old predetermined conclusion in this one and I hope you have time to keep digging..
There’s another—indeed a legendary—Willis in Robert A. Heinlein’s classic, Red Planet. He’s a Bouncer, an amazing mimic, and as it turns out, a Martian young’un.
/Mr Lynn
“gee, I wonder if the continent with the most starvation might, just might have horrible soil for growing crops. Or just rotten farmers …”
Seriously, Africa has good land and FABULOUS resources: Rhodesia exported food by the ship loads, Zimbabwe – the same country – imports it …when it’s not too poor to just starve.
And, truth be told their farmers aren’t stupid, but they live in a society where the concept of “peace, order, good government and freedom” in the pre-1950 Western terms are concepts that are culturally alien, and highly discouraged by their ruling class.
It’s hard to get ahead when you are systematically ground down.
One of the references in this paper is to a study in the US which yielded similar results.
Nonlinear temperature effects indicate severe damages to U.S. crop yields under climate change
http://www.pnas.org/content/106/37/15594.full
The discussion includes the following:
While looking for information on “normal” year to year variability and causes of such variability in corn yields, I ran across the following:
Trends and Variability in U.S. Corn Yields Over the Twentieth Century
http://www.sage.wisc.edu/pubs/articles/F-L/Kucharik/Kuch2005EarthInt.pdf
All would agree that there is some temperature above which yields would suffer and based on current technologies and practices there is some maximum yield. These studies indicate that the limiting (ideal?) temperature is somewhere around 30 degrees C. We can discuss the rate of decline at higher temperatures and it surely is impacted by other climate variables and grower practices. In any case, improved varieties will likely make corn more heat tolerant.
Willis, almost everything about this is wrong.
Even the US corn production map.
Extreme South Florida, Miami Dade County, has over 40,000 acres of corn in production every year. With around 15,000 acres of sweet corn.
South Florida produces around 80% of the countries domestic winter produce.
They would never be able to figure out the degree days for South Florida this way, because they are not smart enough to figure out we plant and grow in the winter.
We grew a patch of sweetcorn in the side yard here in eastern Massachusetts. Came in well for a couple of years, until the raccoons found it. They would grab the ears just before they ripened enough to pick. So we gave up.
Obviously I have nothing of substance to contribute to this interesting thread, other than wondering (as usual) what it would take to get the authors of this pretentious (or is it pretend-science?) journal to come here and defend themselves against Williservation (that’s portmanteau for Willis-eviseration).
So I’ll let Travis Tritt sing mournfully about. . .
/Mr Lynn
“…and it’s worse when it’s dry.”
They really meant it when they said this ‘wasn’t rocket science’……..
The problem with this kind of science, is not in the actual data compilations, but in the sweeping conclusions that are being made, superbly highlighted by Willis in this instance of a 136% decline in yield.
What they have attempted to do, is to observe corn yields and max/min temperature readings and produce a correlation between the yields and degree days. They then take this correlation, having ignored a myriad other factors, such as precipitation, pestilence, strain of corn, fertilizer concentrations, irrigation levels and human inputs, then having apparently disregarded the probability that the correlation arose by chance, and from that formulated a ‘general law’ of corn production, namely the 30 degree day law.
Maybe the actual paper is a bit more cautious than this, but that is the impression being conveyed, and I’ve no doubt that is how it will be portrayed by certain media outlets.
Soil is a big factor. In the midwest the soil is great and corn is the most perfect green 8 feet tall stuff you could wish for. In the south the soil is cr*p and it the corn looks deprived. Corn is a C4 plant and it is very hard to make it too hot for it. I would bet they are confounding water stress–at higher temps the corn is running out of water. But under global warming rain is supposed to increase. Idiots.
“Brazil’s largest summer corn producing states are Parana, Minas Gerais, and Rio Grande do Sul, which account for approximately 17, 14, and 11 percent, respectively, of the total corn crop. Parana also produces a sizable winter corn crop which accounts for nearly 8 percent of the total corn produced in Brazil; winter and summer corn together in Parana account for 22 percent of Brazil’s total corn crop, making Parana the largest corn producing state. The largest winter corn state is Mato Grosso, which plants winter corn after soybeans in a common rotation, comprising approximately 8 percent of Brazil’s total corn production.”
For Parana:
NOAA Station Id: BZ83231
Latitude: 12°33’S
Longitude: 047°50’W
Elevation: 275m, 902′
All of the mean monthly day time temperatures all year are above 86 degrees for Parana.
jan dec avg
87.8 87.3 88.2 89.2 89.4 89.6 90.3 93.9 95.4 91.9 88 87.1 89.8
I would consider the effects of irrigation. Irrigation would lower the temperature in the corn field. The calculated GDD30+ based on the weather station would not be the same as the actual GDD30+ at the field site.
Looking at figure one, and specifically at Zimbabwe, those two circles down at four o’clock represent Triangle Estate and Chiredzi which are down in the lowveld. Up until the beginning of the ‘sixties and the establishment of the Sabi (now Save) River Scheme, the growing of maize, or almost anything else useful in that area, was pretty well impossible because of the heat and the low rainfall. The heat results from the altitude of around 1500 feet, which at about 31 degrees from the equator is not to be sneezed at. The area was transformed with the coming of the Sabi Dam, to, arguably, the most productive land on the continent. Mostly it was sugar cane and fruit, with maize and winter wheat very much of a secondary consideration.
What changed was the availability of water. The heat has not changed in the intervening fifty years.
The three larger circles on the map, much more important for maize production, are along the central watershed and are broadly at 4000 feet and upwards. There the rainfall is higher and somewhat more dependable, but again there is not a great deal of it that is not irrigated. (I speak from a time warp. How much of that farmland is still in production, or has the electricity supply for irrigation I am not sure, but if the power goes off in the lowveld the whole area will revert to bush within a year or two).
I can’t wait for these scientists’ next work to try to tell winemakers where they can and cannot grow a good grape.
If you’ve never sat and talked with a winemaker, I recommend it. Good ones can coax flavor from the seemingly crappiest sand imaginable, in climates the seed is not good for. Many of them have very little science background, if any. Growing things is more art than science.
My apologies for the mistype above. Zimbabwe’s lowveld is about 21 degrees from the equator.
The dec and avg were supposed to be over the last two numbers. I lost the spaces.
I grew up around the Phoenix Metro area of Arizona (BTW could be in the 90s in some areas this week). Some of my friends where Oodham and lived on the Salt River Indian reservation. Some of the families grew corn quite successfully. Amaizeing, you’d have thought that they had been doing it for generations.
BTW, Its the Marxists and their buddies that are the real cause of the problems with African agriculture. Its hard to grow crops when you are running for your life, plus our humanitarian grain shipments that undermine the financial viability of the agricultural industry does not help much.