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.
Watch the Edwards Aquifer levels plummet in March/April as the farmers around San Antonio and Austin irrigate their crops to harvest in late May before it gets really hot.
Well, I think just saying 1*136=136% is probably a bit much, as it would have to approach asymptotically. I would think it is more likely that when temp=X and water=Y, yield=Z.
It could be worse Willis.
Under drought conditions, 136 days would see a crop of -131.2%.
Do they mean ‘one’ bad year can cost nearly two and a half years production?
Texas corn must be tougher than African corn.
Besides changing planting dates, farmers use different varieties of maize for differentes climates (i.e. different temperature and different precipitation). Heat+drought tolerant varieties are grown in hot and dry areas of the world, such as Mexico, or large swaths of South America and Eastern Africa.
Another important point is that the presumed increase in temperature over time is supposed to come from increased CO2 concentrations in the atmosphere. Now, more abundant CO2 has two effects: it may increase photosynthesis, and it may save on water, In crops of the C3 type, like wheat, the main effect is increased photosynthesis; plants get more carbon from the atmosphere, turn it into sugars and thus make more stems, more leaves, more grains. This means increased yields, usually from +20% to +50% with CO2 at 550 ppm, compared to recent measurements of 360-390 (depending on the date of the study). In C4 type crops, like maize, the effects on yields is lower, usually below 25%, but there is a very important reduction in the plant’s water requirement (about -25% to -70%). Thus in hotter and drier conditions even the same variety of maize would yield a bit more and will need less water. In addition, farmers may shift to a more heat-resistant and drought-resistant variety, if need be, and (of course) advance the planting date.
The contrary results one reads from time to time come from studies artificially simulating more temperature and less humidity while keeping all other things constant (planting date, crop variety, CO2 in the atmosphere, farming practices, and so on). This could be (possibly) adequate if you were measuring the effect of a presumed climate change on wild vegetation, but agriculture is not a natural plant-growth process: it is the result of an adaptive interaction between people and Nature; if the climate changes, both the plant and the farmer would respond.
In some extreme circumstances crops would indeed reduce yields and possibly not grown anymore (e.g. if a now-fertile zone becomes a desert), but in general we are talking about an increase of 1-3 °C per hundred years, amid large variations from year to year and from decade to decade. Time enough, and variation enough, to adapt, even if no scientist develops better maize seeds along the next hundred years (which would be very unlikely, because they do it every year).
Hello? ello, llo, lo, o… Echo, cho, ho, o… Now hitting for number 23, Manny Moto!
Willis, you are brilliant. You are smarter than 90% of official degree-carrying scientists out there I am sure. Keep your critiques coming, they are great!
I understand that from your report we have no detail of the study, but what strikes me immediately is that a fair proportion of the trial areas are in Zimbabwe. Due to the politics in Zimbabwe the country is a basket case! It has gone from being a major food exporter to chronic famine. My question is: How much of the reduction in yields is due to to Zimbabwe’s collapse and is this reduction mimiced in the other areas?
I would suspect (without any evidence) that this study shows more about the effect of political megalomania than temperature.
Credentialed, not educated. And in this case, the warmists aren’t even aware of basic, common-sense reality.
Except they probably got a lot more govt. money.
which according to the L2011 results should reduce yield by 136% … 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.
I think it’s called an asymptote.
Hilarious! The folks that did that study obvious didn’t think about other parts of the world where corn is grown…
Gee, hard to grow corn in Africa? Why? Fertilzer (or lack of)? Consistent irrigation (or lack of)? Farming skill (or lack of)?
Check the elevation. Some areas look to be 1km elevation. Isn’t water loss increased at lower air pressure?
Hey! No fair adapting. Or moving. You have to stand still and perish,else the rhetoric doesn’t work.
This Nature article is complete BS.
There are many species of maize/corn, some more drought or heat resistant than others.
This is like comparing apples with pears and strawberries.
You plant the species of corn/maize which is best suited for the climate in your area. That’s why there is corn/maize from Toronto in eastern Canada to northern Florida – even the goofiest alarmist should realise the difference in climate between these two areas.
And more varieties of corn/maize are appearing every year.
US farmers can likely adjust to lots of things if the government doesn’t get overly involved. And some scientists actually have to earn their salaries, such as these folks that have been working on drought-tolerant corn.
http://www.hpj.com/archives/2011/feb11/feb21/0204DroughtTolerantCornMRFE.cfm
should it decrease by (.99)^136 ?
Study region map shows what’s rigged. They mixed in lots of weather data from desert Mali/Niger/Sudan, arid Namibia and N.E South Africa for a majority of East African maize trials centered in old productive Rhodesia /Zimbabwe , narrow Malawi and recovering socialist Tanzania.
The Zimbabwe maize yields themselves are unreliable, since agricultural production has infamously suffered from a unique form of man made disaster. The study should release it’s specific data from all of Malawi, since it seems there were meteorological stations and plenty of maize plots all over that country..
A few other fcts to add …
http://varietytesting.tamu.edu/corn/2009varietytrials/cornyieldresults/GulfCoastCornHybridPerformanceTrials2009.pdf
suggests that yields in Hildago County (Edinburg TX area) are about 40-50 bushels per acre.
Yields in a prime area (Iowa http://www.extension.iastate.edu/agdm/crops/pdf/a1-14.pdf) are about 160 bushels per acre. In excellent years the yield is close to 200 bushels per acre. That looks like a ~ 75% reduction in yield due to the warm TX summers. While this is not over 100% drop, it is still in the right ballpark, especially for a locale which presumably would be an outlier in the temperature ranges used in the studies .
(By coincidence, if you treat the “1%” reduction in a “compound interest” sort of manner, the drop would be (0.99)^136 = 25% of the optimal yield. I have no idea if this is consident with the original analysis — it is just an observation).
One solitary degree day causing a 1% drop in corn yield is a number that just doesn’t sound right to me. My guess is that it’s something like per day.
During a 150 day growing season, that would give a US style measurement of 150 degree days, causing the 1% drop in yield. That may be too little response, but it sounds more reasonable to somebody (like myself) who has no farming background.
Regardless, Willis, I agree with you that farmers simply would adjust their planting and harvesting dates, so the study seems moot to me. BTW, I noticed that the study looked at tropical and sub-tropical locations, which may not be the best choice of where to grow corn.
A quick comparison shows that the corn producing regions don’t correlate with US precip maps, as long as there is a minimum amount of rainfall. The corn belt has prairie type soils combined with relatively flat ground. South of Iowa, Illinois, Indiana, and Ohio, you have very hilly terrain suitable for only small patches of farm ground.
Texas corn stops at the hill country, and same with the southeastern states. Corn also follows waterways, river bottomland.
Thanks Willis!
There is more then one county that grow corn in FL. It may just not reach ‘minor crop’ level.
http://fciig.ifas.ufl.edu/scpmap.htm
Willis: If you experiment with the Wolfram Alpha degree-day calculator, you will probably find that it calculates degree-days differently from this paper. If you set the temperature equal to 95 degF, you’ll see no day where the average temperature was over 90 degF, but there still will be 11.8 degC-days of cooling. I suspect they are calculating deg-hours above the chosen temperature (a sensible measure of the demand for cooling) and then dividing by 24 hours/day. This is not what is done in the paper, which is publicly accessible at http://iis-db.stanford.edu/pubs/23138/Lobell_2_11_NatureClimateChange.pdf
In Figure 2, did you notice that the two standard deviation error bar on the reduction in yield is the same size as the reduction in yield without drought? Could that be the reason why the authors did not include any estimate of uncertainty in their 1.0% and 1.7% reduction in yield per deg-day of excessive heat.
You are completely right, adaption is the solution. If you look at Figure 2, corn is currently being growth in Kenya, where the average temperature during the 150-day growing season is >30 degC.
Another Willis masterpiece!
How does he keep ’em coming?
Nice of nature’s tame “scientists” to act as the butt of Willis’s wry humour!
The bunch of clowns. Does someone pay ’em for this crap?
I know when I lived in Ohio (in the light green area but close to the dark green, an important factor for planting time was whether it was warm enough and dry enough to put the corn in. If not (or the farmer just ran out of time) the land was switched to soy beans (which have a shorter growing season. So if the climate gets warmer, the farmers will have an earlier start to the planting season and probably more time for the fields to dry out enough to be planted.
BTW, soil is a big factor in planting corn and the dark green areas are basically areas where there were glaciers which helped to create rich soil. The SE areas in Ohio are below the terminal moraines and thus both hilly and not having much soil.