Guest Post by Willis Eschenbach
There is a new paper out in the Proceedings of the National Academy of Sciences called Linkages among climate change, crop yields and Mexico–US cross-border migration (hereinafter L2010). It has Supplementary Online Information (SOI) here. The editor of the paper is (the late) Dr. Stephen Schneider.
The paper basically advances the following theory of linkages:
Climate Change —> Reduced Mexican Crop Yields —> Migration to US
Hmmmm … their Abstract says:
Climate change is expected to cause mass human migration, including immigration across international borders. This study quantitatively examines the linkages among variations in climate, agricultural yields, and people’s migration responses by using an instrumental variables approach. Our method allows us to identify the relationship between crop yields and migration without explicitly controlling for all other confounding factors. Using state-level data from Mexico, we find a significant effect of climate-driven changes in crop yields on the rate of emigration to the United States. … Depending on the warming scenarios used and adaptation levels assumed, with other factors held constant, by approximately the year 2080, climate change is estimated to induce 1.4 to 6.7 million adult Mexicans (or 2% to 10% of the current population aged 15–65 y) to emigrate as a result of declines in agricultural productivity alone.
Although the results cannot be mechanically extrapolated to other areas and time periods, our findings are significant from a global perspective given that many regions, especially developing countries, are expected to experience significant declines in agricultural yields as a result of projected warming.
YIKES! … scary. Makes a man think seriously about mitigation.
I often divide things into the good, the bad, and the interesting. Regarding this study, first, the good. The authors have done a workmanlike job of pointing to the data that they used, all of which is online. This is to be highly commended, as it allows a quick determination of the validity of their work.
Next, the bad.
Because they were clear about their data, I was able to replicate their results exactly for the corn yields. My practice is to make replication the first step in any analysis of this type. It verifies whether they have done what they say they have done. In doing so, I discovered a most curious thing.
First, a small digression. “Yield” is how many tonnes of a crop are produced per hectare (or acre) harvested. Yield is affected by a number of things, including location, soil quality, and climate. If the yield in a certain location starts to fall, this is an indication that something is going wrong in the farming cycle in that location.
The curiosity that I discovered is that the paper calculates “yield” in a way that I had never seen. Yield is defined as how much crop production you get for every hectare (or acre) that was harvested. The authors, on the other hand, calculated yield as the amount produced for every hectare (or acre) that was planted. This often yields a very different number.
The source of their data is here. Click on the “Maiz Grano” (Corn) in the first column, mid page. On the resulting page, click “Producción” (Production), second button from left. Then look in the far left column and click on the “Anuario” (Annual) button. Select 2004 as the year (“Año”) and press the “Consulta” button.
Now take a look at the data for 2004. The headings are:
Ubicación, Sup. Sembrada, Sup. Cosechada, Producción, Rendimiento
Or in English
Location, Area Planted (ha), Area Harvested (ha), Production (tonnes), Yield (tonnes/ha)
Over the period in question (1995-2004) Baja California averaged about 3 tonnes of corn per hectare. For Baja in 2004, their site says
BAJA CALIFORNIA, 592 hectares planted, 10 hectares harvested, 25 tonnes produced, yield 2.5 tonnes/ha
Note that, in common with other authorities, the Mexican web site itself calculated yield as production divided by area harvested, not divided by area planted. This is the normal definition of “yield” used by all other analyists. For example, from the UN Food and Agriculture Organization (FAO) web site glossary we have (emphasis mine):
Title: Crop yield
Definition:
Harvested production per unit of harvested area for crop products. In most of the cases yield data are not recorded but obtained by dividing the production data by the data on area harvested. …
“Harvested area” in turn is defined as:
Title: Area harvested
Definition:
Data refer to the area from which a crop is gathered. Area harvested, therefore, excludes the area from which, although sown or planted, there was no harvest due to damage, failure, etc. …
From this, it is clear that the authors of L2010 are not calculating the yield correctly. They have calculated the yield for Baja 2004 as 25 tonnes / 592 hectares planted = 0.04 tonnes/ha, a meaningless result. This is why yield is always calculated based on the area harvested, not based on the area planted. Obviously, something happened in Baja in 2004 that wiped out most of the corn crop. But for the remaining area, the yield was 25 tonnes / 10 hectares harvested = 2.5 tonnes/ha, not far from normal.
Overall, this is a very significant error. To take one example of the effect of the error, Figure 2 shows the correlations between Mexican annual temperatures and corn crop yields (correctly and incorrectly calculated).
Figure 2. State by state correlations between annual temperature and corn crop yields, 1995-2004. “Yield” is production / area harvested. “Incorrect Yield” is production / area planted, as used in L2010.
Note that in some States (Aguascalientes, Campeche, Yucatan), one dataset shows a very small correlation between temperature and yield, while the other shows 20%-40% correlation. In some cases (Nueva Leon, Queretaro, San Luis Potosi) one shows positive and one shows negative correlation. Overall, there are many results which are significantly different.
Because the correlations of the yield are central to their analysis, this error invalidates the paper and requires the recalculation of all the relationships. Remember that their thesis is:
Climate Change —> Reduced Mexican Crop Yields —> Migration to US
Note that there are two separate mathematical relationships in their claim. One relates climate change (temperature and rainfall) to changes in yield. The other relates changes in yield to migration rates. An error in the yield, therefore, requires a recalculation of both relationships, with new error bounds, etc.
Since the original web site is in Spanish, this error may simply be a misunderstanding of what the web site says. However, that slides over the question of why they didn’t simply use the yield figures provided in their data source …
I have posted up the Area Planted, Area Harvested, Production, Annual Temperature, and Yield figures here as an Excel spreadsheet. To determine which one they used (area planted or area harvested), it is necessary to take 5-year averages of the data (1995-1999 and 2000-2004) and compare the answers to Table S1 of the Supplementary Online Information. I can reproduce their results only by the incorrect usage of area planted instead of area harvested. Note that “Log Corn Yield” in Table S1 of their paper is the natural log (ln) of the yield.
I have pointed out some good about the study, and some bad, so onwards to the interesting. One interesting thing to me is the variety of responses of different states to increased or decreased temperatures. In a third of the Mexican states, warmer is better for corn (positive correlation). In two-thirds of the Mexican states, on the other hand, cooler is better for corn. Hmmm …
Another interesting thing is the change in the Mexican country average yield for corn. Figure 3 shows both the country average yield and average annual temperature for 1995-2005:
Figure 3. Mexican Corn Yield (red line, left scale) and Temperature (blue line, right scale) Photo Source
Fig. 3 highlights one of the real shortcomings of their study. This is the very short time period that they are investigating. However, taken at face value, this graph does not give much credence to the idea that increasing temperatures will reduce Mexican corn yield … (note that I make no claim that this relationship is meaningful or statistically significant. I only say it does not support the authors’ argument.)
As noted above, there are two mathematical relationships involved in their claim. One is temperature/precipitation vs yield, and the other is yield vs emigration. For the yield vs. emigration, the Mexican dataset is short. So I understand that they have to make do with what they have. But yield versus temperature has a much longer dataset. The temperatures from their source span 1971 to the present, and the state-by-state crop data goes back to 1980. So they should have established the corn yield/temperature link using all of the data available (1980-2009), even though the other yield/emigration link has so much less data.
How does something like this get published? I suspect that this is another example of a member of PNAS using their “Proceedings” publication as a vanity press with little in the way of peer review. The article is edited by Stephen Schneider, who also edited the other recent “blacklist” paper, so it’s clandestinely flying across the border under the peer-review radar …
Hopefully, this will be the last of the posthumous Schneider “science” for us to deal with. The only good thing about Schneider was that when I saw his name on something, I knew I could likely find errors in it … made my job that much easier.
Look, I don’t like to speak ill of the dead. Stephen Schneider was probably a nice man who loved his family and petted puppies and brought the homeless blankets and dinner. But his general claims were often a “post-normal science” abomination, and his scientific work (as in the present instance) was sometimes very slipshod.
In particular, Schneider is noted for his statement regarding the obligations of scientists:
To capture the public imagination, we [scientists] have to offer up some scary scenarios, make simplified dramatic statements and little mention of any doubts one might have. Each of us has to decide the right balance between being effective, and being honest. This ‘double ethical bind’ we frequently find ourselves in cannot be solved by any formula. Each of us has to decide what the right balance is between being effective and being honest. I hope that means being both.
To me, the most scary scenario is scientists who balance their honesty with effectiveness, or with anything else for that matter. I don’t want scientists who make little mention of their doubts. I don’t want scary scenarios from scientists, that’s why God made Hollywood and the BBC.
I want scientists who are as honest as possible, about their doubts and everything else. Schneider’s view, that scientists should balance honesty and effectiveness, is extremely and insidiously dangerous to science.
So, as un-PC as my view might be, I am overjoyed to see the last post-mortem gasp of Schneider’s apocalyptic alarmism. Am I glad he is dead? No way. As the poet said,
Each man’s death diminishes me,
For I am involved in mankind.
I am very happy, however, that he is no longer teaching at Stanford, that he is no longer writing garbage for me to wade through, and that he is no longer busily filling up the porches of the Stanford students’ ears with “cursed hebenon” …
My regards to all,
w.
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Tim Clark says:
July 29, 2010 at 6:39 am
Tim, as you indicate, you “consider yield/acres planted as a good parameter to distinguish crop loss resulting from insufficient water as opposed to crop loss resulting from incompetent production practices”. First, I think you mean “production/acres planted”, not “yield/acres planted”.
In Baja California in 2004, out of 592 hectares planted, 582 of them provided no crop at all. However, the remaining 10 hectares were able to produce at about the normal rate. Is it your claim that this was due to “insufficient water”? Because I doubt that very, very much. None of these hectares were irrigated, so why would 10 hectares do fine in your supposed drought, and all the rest of them die?
Finally, you say that you use the production/acres planted to determine catastrophic loss. But the L2010 analysis is not looking to determine catastrophic losses, it is looking for a relationship between corn production and temperature/precip.
Hu McCulloch says:
July 29, 2010 at 10:29 am
Hu, the problem is that they are trying to relate climate to crop yield. They are related, there’s no doubt of that. But including occasional catastrophic failures from unknown causes will not improve the accuracy of the results. You seem to assume that all crop failures are climate related. I can assure you that is not true.
I’m not following that. What does that have to do with using area planted?
For the nth time, yes, that is possible. But if that is the case, the authors of the study need to state it and justify it. That is to say, they need to show why they are using an unusual measure, and they need to show that it is the diet that is causing the sprinter to stumble. They have done neither.
There are literally hundreds of studies relating yield and climate. I know of none that relate production/area planted and climate. So if they are striking new ground with this study, they have an obligation to note that and justify it. But they didn’t. Which is why I say that it was an error, rather than being deliberate.
Does that “render the article meaningless”? Well, depends. If it is an error, and they thought they were using yield, then they need to re-do their calculations start to finish. This makes the article meaningless.
On the other hand, if it was deliberate, then it does not make the article meaningless. It just renders it wildly and hideously incomplete, as they have not laid the foundation for using some off-the-wall measurement in their analysis.
Overall, I am astounded by people defending the use of production/area planted when it seems pretty clear, from the lack of the normal explanations that are used to introduce a novel metric, that the authors had no idea that they were not using the standard definition of “yield”.
Hu McCulloch says
“If an acre was really planted, it was withheld from other crops, grazing, industry, or other land uses. Also, the farmer went to the expense of ploughing or drilling plus the cost of the seed. If it’s not worth harvesting this is an even bigger failure, perhaps, than merely obtaining a low product per acre harvested.”
This would be correct if the object of the excercise was to budget for the cost of production. In these circumstances, the fixed costs would have been absorbed into the whole acreage planted, and the losses would have been written off to the profit and loss account as lost revenue.
However, this is not what is being done in this research. As a scientist, you are looking at the effect of climate change on yield. This would likely lead to lower yields but not to catastrophic loss. If catastrophic loss is observed to occur through climate effects, then you need to show this. You need to document that the acreage was not harvested because the corn didn’t ripen or such. You have to separate these things from non weather events, such as disease, fire, strikes. If you can’t do that then you should stick to the areas harvested to reduce the noise.
“If a perverse diet causes a sprinter to stumble off the blocks, that should count against the diet as much as slow times without stumbles.”
Your response to the sprinter analogy is competely absurd. If it is the researchers belief that the diet is causing the sprinter to fall around and stumble (highly unlikely), he would be taken to a medical specialist for tests in order to eliminate that possibility. If this is in fact the case, then the result is not that the diet makes the sprinter run slower, which would be the outcome of including such a test run, but that the diet makes a human ill. In other words, the hypothesis has been invalidated and replaced with a new one. This mirrors the harvesting problem. If the researcher believes that climate change is causing thousands of acres to not be harvested, then he needs to zoom in and study these effects on their own. In no way can he just include them carte blanche in the results.
If an undergrad turned in a third year project like that he would be failed for the reasons I have given. But even before that point, the tutor would have put the same questions to the undergrad as Willis is asking. It’s just basic science.
Bill Tuttle says:
July 29, 2010 at 1:57 am
Jim D: July 28, 2010 at 10:07 pm
Have you ruled out that pests/fungi can relate to climate in any way? Hint: how about pine bark beetle?
I was gonna say something snarky about pine bark beetles and corn, but I’ll just observe that beetle infestations only explode in the absence of wildfires, which normally limit the population.
———-
Ah yes, the infamous pine beetle story. One of my favourites. You are right about the role of fire but it is slightly more complicated. The key point is that the pine beetles need mature trees to attack, with a suitably think cambium layer – which is their actual habitat. So the role of fire is to kill off pine trees before they get large enough for the beetles to attack.
This is most evident in the lodgepole pine – the one that made most of the AGW alarmist headlines in British Columbia – which is a fire-adapted species that maintains its dominant role in large areas via periodic wildfires which burn them (and their competition) while simultaneously releasing their seeds. This creates even-aged but usually short-lived stands. The recent problems have been created by the Smokey the Bear mentality which suppressed these fires, allowing vast areas of mature even-aged lodgepole pines to survive, thus creating vast expanses of potential beetle habitat. Add a few warmer than usual winters and this set the stage for the massive beetle epidemic that made the headlines. The botom line is that this never could have happened no matter how warm the winters were if this totally unnatural forest situation had not been created by human fire suppression.
Other pine species have slightly different dynamics but this beetle problem, and other problems, all go back to Smokey the Bear’s interference in natural processes.
The beetle is always there, picking off weakened mature trees, but unless stressed by drought or disease, or overwhelmed by the kinds of numbers produced by these recent epidemics, most trees can resist their attacks.
This story became entirely ridiculous when the epidemics were at their peak in British Columbia and spreading into Alberta. There were hysterical stories about how it was going to spread across Canada and kill off every tree – but since this beetle is specifically adapted to lodgepole pines at that latitude, it could never have gone any further than the range of that species. This was fueled by reports of the beetles attacking the odd spruce in BC, but that was simply due to the incredible number of beetles attacking anything… and they cannot survive in spruce trees.
That Canadian epidemic is over by the way. The beetle ran out of mature lodgepole pines (and ponderosa pines further south) and that’s the end of the story… unless they allow the same situation to develop in 80 years (for the lodgepole pine). And, since many areas are now just standing firewood sprinkled with pine cones ready to pop open with the next fire, the ingredients for that are all there.
Fire suppression is the root cause of some other supposed AGW tales. The intense fires in California are the result of unnatural fuel buildups due to the suppression of fire. The Native Californians were not so stupid. But now its much more complicated as there are so many houses built in areas that will, inevitably, burn.
It doesn’t matter how warm or dry it is if there is no beetle habitat to support epidemic populations, or fuel to burn. But don’t tell that to the AGW gang.
If one is going to do a study of the *yield* as defined in the paper, they would have to describe exactly why the various acreages were not harvested. I mean EXACTLY. Anything less is not science. I suspect they did not have access to that kind of data which means, as we all know, the paper should have been abandoned.
As nice as Willis tries to be, I can’t see anyway that this was a mistake. They did exactly what they set out to do.
What this report does not mention is that global warming may render Canada inhabitable in which case some of those immigrants may keep on going, all the way to Saskatchewan.
When the Ice Age hits the migration will be in the opposite direction.
I read the article and it is worthless.They assume that CO2 levels of 555 ppm by 2080 will raise global temperature by 1 to 3 degrees and then calculate that without CO2 fertilization this will reduce Mexican crop yields at least 39 percent. Or, with fertilization, only 10 to 15 percent. And this is supposed to send millions of immigrants to us! First of all, inclusion of the no-fertilization figure is just scaremongering for addition of carbon dioxide to air clearly promotes plant growth – that is what the fertilization is all about. Secondly, I have shown that anthropogenic global warming has never been observed and Ferenc Miskolczi has shown that this is because it is physically impossible. Hence, there will be zero warming by 2080, higher atmospheric carbon dioxide, and improved crop yields in Mexico. It could just possibly lure back some of the Mexicans who are here now.
I noticed both Tim Clark and others are assuming the seed was purchased and Modern farming techniques are used.
1. It could have been farmer “saved seed” This means the seed selected will be optimize for the cultivar that best grows in that micro-climate. Unless the climate changes rapidly there should be adaption. (That is why Monsanto set up seed banks to grab the genetics)
2. Modern farming techniques are used.
The Mexico I visited for three weeks was still using burros. Remember too that the government cut subsidies to farmers. That could mean the planting of “store bought” hybrid cultivars that needed fertilizer and pesticides to grow well but not having the money to fertilize and spray if the subsidies were cut. Also thanks to NAFTA the market was flooded with cheap American corn. The farmers could very well have walked away from the crops and the land due to bankruptcy. Remember Mexico lost 75% of the farming population in about ten years. Or it could have been just politics. (read the yellow column on the right) http://newfarm.rodaleinstitute.org/international/pan-am_don/july04/index.shtml
The experience in India with the Monsanto GMO cotton shows this can happen.
“Worse, Monsanto seed has been genetically engineered so as to require the use of Monsanto herbicides and fertilizers….
The history of GMO crops in India is like elsewhere. The first few years are great then they need more herbicide and more fertilizer [and more water] to get yields and that drives the farmer into bankruptcy. India has had a rash of farmer suicides due to crop failures. They didn’t have this with indigenous seeds. The costs were much less and they could muddle through.” http://www.nakedcapitalism.com/2010/02/india-defies-monsanto-says-no-to-gmo-crops.html
GMO corn was banned in Mexico but tests showed that the genes had jumped the border and were showing up in Mexico. Perhaps the case can be made that the decline in yield per planted acre is because of the Monsanto genetics, especially if the corn has the terminator gene and failed to germinate. Or if it germinated but as was the case in South Africa failed to produce ears of corn.
“South African farmers suffered millions of dollars in lost income when 82,000 hectares of genetically-manipulated corn (maize) failed to produce hardly any seeds.The plants look lush and healthy from the outside. Monsanto has offered compensation.
Monsanto blames the failure of the three varieties of corn planted on these farms, in three South African provinces,on alleged ‘underfertilisation processes in the laboratory”.” http://www.digitaljournal.com/article/270101
Looking at acres planted vs amount harvested and declaring it was caused by global warming is just plain sloppy, lazy and incompetent. Don’t these people have any sense of curiosity, don’t the want to find out WHY the fields were never harvested?
” For Baja in 2004, their site says
BAJA CALIFORNIA, 592 hectares planted, 10 hectares harvested, 25 tonnes produced, yield 2.5 tonnes/ha”
This glaring statistic should have someone asking WHY!!!
It could be as simple as a change (thanks to US salesmanship) from growing white corn to growing yellow corn, a corn that is harder to produce.
Determining the Feasibility of Yellow Corn Production in Mexico
http://ageconsearch.umn.edu/bitstream/46741/2/Microsoft%20Word%20-%20SAEApaper1.pdf
Sorry, but I don’t see any relation to temperature. The issue is water as in rain and irrigation. Temperature is not an issue and the correlation is false, as it always has been, unless there is an unexpected frost, and I don’t think that is happening in Mexico any time soon.
My other point on the statistics was that the authors found a correlation using their definition of yield. If this indeed had a random component due to crop non-harvesting for non-climate reasons, the way Willis defines yield should give even stronger statistics. Which definition has the highest correlation to climate? Doesn’t Willis’s suggested definition just make the situation worse by removing what he says is a random component? Anyway, I suspect the authors have a definition that correlates better to climate, because surely planted acres are more constant year to year than harvested acres (I’m guessing), making yield normalized by that more meaningful in absolute terms.
Thanks for the scientific review effort, Willis, but given the fact that a form of the prime CAGW/PNAS “tenet” was sufficiently implied by its title, the authors and PNAS reviewers already knew that the remainder of the paper was irrelevant./sarc.
But just for the record, the statement, Climate change is expected to cause mass human migration, including immigration across international borders….Depending on the warming scenarios used and adaptation levels assumed, with other factors held constant…., seems to say once again that, according to Climate Science, “climate change” is only possible as a result of Anthropogenic causation.
Such that any “other factor” which we might otherwise say involves a natural move to a different climate situation now simply can’t be called “climate change” anymore, obviously including even any truely natural warming.
So, ftr, this is an example of the same old Armchair creation of “reality” via word-games which characterizes Climate Science – but certainly having nothing to do with the use of the Scientific Method to try to describe and deal with reality, or with any genuine attempt to retain the usual meaning of words so as to communicate effectively to and with people and especially where these things involve truely helping out Humanity.
Jim D says:
July 29, 2010 at 9:21 pm
I’ve only looked at the annual temperatures. The correlation of annual temps with true yield is only 0.03, and with the bogus yield it is only 0.07. Neither of these are statistically different from zero (or from each other, for that matter).
Willis Eschenbach says:
July 29, 2010 at 12:15 pm
Tim, as you indicate, you “consider yield/acres planted as a good parameter to distinguish crop loss resulting from insufficient water as opposed to crop loss resulting from incompetent production practices”. First, I think you mean “production/acres planted”, not “yield/acres planted”.
Willis, the government interprets things in strange ways. Since deficiency payments or disaster payments are allocated (under the FB2008) on a multicounty (called management units) area, entitlements are based on that regions average yield/planted acreage. Farmers must submit (for DCP payments) to the Farm Service Agency (FSA) the acres planted of each crop planted. Then submit their yields. The database then kicks out average yield/acres planted. If the region falls below a certain threshold, any farmer who suffers a loss below the threshold receives a payment. Never in my experience has there been payments for crop loss resulting from any condition other than drought (~75%), hail(~15%) or early freeze (~10%). In perusing the database accessible to me, there has never been any deficiency or disaster payments made resulting from attribution to temperature. So in essence I guess I didn’t make my point clear. Regardless of how anybody mathematically determines crop loss, it ain’t due to temperature, to which we can both concur. This paper is bunkum.
Is it your claim that this was due to “insufficient water”? Because I doubt that very, very much. None of these hectares were irrigated, so why would 10 hectares do fine in your supposed drought, and all the rest of them die?
Yes, that’s my claim. Based on statistical probability. Willis, 500+ hectares in the entire region. Out of how many. Thats about 1500 acres. My county has 150,000 + acres under cultivation.One timely rain event, localized over a very small portion of the region would make or break the crop. Here in Kansas, in the county I work, wheat yields ranged from 60+ bu/acre in the eastern hardland area to 30+/- in the western sandy loams. And yes, the higher yield area received about three .3/4″ to 1.1″ rain events. It makes that much difference over a spread of 30 miles. Of course the soil types influence yield, which is also in play in the Baja.
But let me digress, if you could find out what was actually done in the non-harvested acres, I think you might be suprised. I’ve been to that area and many of the farmers ensile corn. So it may not have been harvested for grain, but was harvested. Again, I think this study is bunkum.
Finally, you say that you use the production/acres planted to determine catastrophic loss. But the L2010 analysis is not looking to determine catastrophic losses, it is looking for a relationship between corn production and temperature/precip.
Well, I do get your point here. But I reiterate my main thesis that without access to precipitation data, this study is bunkum.
Actually, the “early” freeze should read “late” freeze. Need more coffee.
Willis, the authors say this.
We suspect that weather has always been an important factor in the agriculture-emigration relationship, as
many of the migrant-sending regions of Mexico have extremely variable rainfall
(S34).
Extremely variable rainfall and the average rainfall in that region is only 14″/yr. They grow white corn. This is probably a dead thread. I’m not really disagreeing with you Willis, I appreciate your hard work here. I just think it’s the water, whose amount is not influenced by [CO2].
In some of our analyses, we
combine corn and wheat to form a measure of combined crop yields. When doing so,
we convert wheat production into equivalent corn production units using their price
ratios calculated from the national weighted average prices for a given year.
Just more bunkum
I see no reason to think that a low harvest rate is necessarily due to catastrophic events — an entire growing season that is too hot or too cold or too dry or too wet or too sunny or too cloudy might render the crop not worth harvesting, so that the harvest rate is at least as worth correlating to temperature as the harvest yield. The planting yield simply combines the two into one statistic. It might have been useful to disaggregate it into its two components, and it might have been confusing, in this literature, to call the planting yield “the yield” rather than the harvest yield, but I still don’t see this statistic as wrong per se.
Of course, this is not to say that the study is any good — If, as you say above, the correlation with temperature is insignificant no matter which way “yield” is computed, then there isn’t much there. The authors should have been clearer that they were not using the conventional measure of “yield”, but I don’t see their measure as instrinsically “bogus,” as you put it.
An unexpected fall in price would affect the harvest rate adversely, but would also increase the average harvest yield, since only the fields that did best would be harvested, so neither measure is exempt from such noise factors.
From
http://rogerpielkejr.blogspot.com/2010/07/silly-science.html
“One of the paper’s authors, Michael Oppenheimer, a Princeton professor and lead author of the forthcoming IPCC report on extremes explains his motivation with the paper:
Our primary objectives were, No. 1, to give policymakers something to think about and, No. 2, to give researchers a spur to start answering some of the more complicated questions
“
Hu McCulloch says:
July 30, 2010 at 7:27 am
Hu, I’ve been studying the effect of climate (and other factors) on crop yields for some years now. I have never seen anyone use production/area planted as a measure of yield. I suspect that this is for the reasons and difficulties I enumerated above.
While it is possible that they are using that measure deliberately, it seems very doubtful because they call what they are using “yield”, and they have made no attempt to explain or justify the use of a new measure.
Tim Clark says:
July 30, 2010 at 6:00 am (Edit)
Tim, you make my point (I think). The use of production/area planted is an indicator of catastrophic loss. But that is not what the authors of L2010 were looking at. They were looking at long term changes in yield due to climate, not catastrophic loss for whatever reason.
However, I still doubt that the metric used is yield/hectares (or acres) planted as you repeatedly claim. Suppose two farmers have planted corn, and both have a yield of say two tonnes per hectare. One farmer planted 100 hectares, and the other planted 10,000 hectares.
One farmer would have a yield/hectares planted of 0.02, and the other would have a yield/hectares planted of 0.0002 … how is that meaningful on any planet?
I might indeed be surprised. But given that we don’t know, it is very difficult to find out, and we might all be surprised by the reasons for the catastrophic losses, I agree with you that the study is meaningless.
An easy way to overcome all of this silliness, and illegal immigration, and lawsuits would be for the Mexican government to actually make all their citizens feel that living in Mexico with friends, families, customs was better than running away to join the gringos .
Like any country the primary responsibility of the Mexican government is to make the place work well enough to be attractive to it’s citizens. Africans run away to the west and endure all kinds of privations, racism being one, rather than live under their own governments.
Why can’t Mr Calderon make Mexico sufficiently attractive to his own people? Don’t tell me it is because of an unfair planet because Mr Calderon got his job by saying he could do just that. Same as Mr Obama or Mr Mugabe.
That’s the problem I suppose, the American way of doing things at home is just so much better than so many other places. The third world loves to denigrate America yet it’s citizens “lie awake in bed at night dreamin’ ” of moving to the USA. When they get there most fit in and up their game but some try and drag it down to the standards they left behind.
America’s success is it’s own weakness.
@willis
In my opinion illegal Mexican immigrants are for the most part scapegoats of convenience for problems actually caused by poor social and fiscal policy. Ultimately the responsible party for these poor policy choices are the voters. Illegal immigrants don’t vote.
Texas has traditionally had a rather open border with Mexico. Except for a recent rise in drug related confined to very near the border it has never been a problem. And even in that case the traffic is driven by demand for illegal drugs from legal US residents so it’s still us who are ultimately at blame.
Illegals in Texas used to cross the border almost like commuters. Men would cross the border to work, stay a month or three, living as cheaply as they can sharing low-rent apartments and car pooling, and send their earnings back home to their wives and children. Women crossing the border tended to be live-in domestic care takers which allows both parents to work at high paying jobs. Texas residents in turn get their homes built at lower cost, lower cost produce, landscape maintenance, inexpensive live-in domestic help, and things of that nature. The savings produced by the low cost labor are then available for the purchase of a huge range of goods and services that illegal immigrants don’t provide.
Problems are caused largely by poor choices in social policies. Anyone born on US soil automatically becoming a citizen is a huge mistake. Citizenship should come either through naturalization or inheritance from citizen parents and no other avenue. Forcing emergency rooms to provide care to anyone at all who walks through the door is another mistake. Public schools admitting all children regardless of parental citizenship is another mistake. If it weren’t for these boneheaded policies we wouldn’t have a problem. The blame for these boneheaded policies lies squarely on the voters who must be citizens in order to vote.