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.
wsbriggs says:
July 28, 2010 at 2:22 pm
“Among other questions, the whole study begs the question, at what altitude were the crops being grown? If the 1/3 with positive correlation were at high altitude (were all other things being equal, we would expect lower temperatures), and the 2/3rds at low altitude, the one could reasonably expect that increasing temperatures would cause distress in the plants, were all other things equal.”
Altitude is not a big issue in Mexico, as it is in the Andean countries, especially Peru and Bolivia. Main problem in Mexico is water. H2O is in excess at the low-altitude South, where less than 1/3 of population lives, and scarce in the relatively higher elevation North where more than 2/3 inhabit. Watertables are descending throughout the North, and precipitation is lower. Current IPCC models predict reduced humidity in the North, thus mandating thorough modernization of irrigation systems to improve their efficiency (most commercial agriculture is in the North). This is indeed already taking place, and would undoubtedly keep proceeding in coming decades. Same is valid for the semiarid Brazilian Northwest, where drip irrigation and other pressurized irrigation systems have been driving the increase in irrigated area since the 1980s, quintupling that area in recent decades and with ample margin to continue improving water availability and the efficiency of water management (number of smallholder subsistence farmers and poor agricultural workers is also declining there: Brazil would be 94% urban by 2050, and more than that by 2100; fortunately, more than half of the Northeast, in fact the most populated part, is expected to enjoy increased precipitation as a result of IPCC-predicted climate change).
This is news? Food supply has been a major driver of migration since time began. And not just for people. Think bison for example. Or any other critter. Animals fight over food and water. I see it on a daily basis in my front yard. Duh.
Ah… another great example of ‘stupid farmer’ syndrome!
In the real world if the local weather regime changes, so do the crops. This is first done by changing the variety grown, but if the regime change becomes drastic, the different species of crop will be grown.
I live in the country and know many farmers who are very good at making these decisions – their livelihood depends on it. Stupid farmers do not survive for long!
As ever, the cargo cult science of CAGW thinks nothing will change in the future and people will continue doing exactly what they do now. However, history shows we have always adapted to survive and we will continue to do this in the future.
Thanks for your scrutiny, Willis.
Sigh, I just got through reading the writings of people obviously not familiar with agriculture, or immigration, and apparently a fairly sparse knowledge of the effects of warming on plant life in general or in history.
The immigration from Mexico wouldn’t have other factors such as, uhmm, I don’t know, maybe BECAUSE THE ENTIRE SOCIAL FABRIC OF THEIR SOCIETY IS CRUMBLING UNDER THE WEIGHT OF THE DRUG LORDS!!!???!!! They are literally, in broad daylight, executing police officers. There is such a wanton disregard for authority and law in so many places, it is a small wonder people are trying to escape their country.
There are so many flaws in the paper, I don’t think its worth the time to go over them all. I’ve already spent more time on this than it warrants. I honestly don’t know how hot it has to be to thwart crop yields, but we haven’t got anywhere close to that. CO2 causes plant growth. Immigration occurs for many reasons, but I’m trying to think of one instance where a large segment of a population moved to cooler climates in forms of migration or immigration in search of a cooler climate……nope, can’t think of a one. Perhaps there is an example out there somewhere, I’d be interested if someone could come up with one example.
Perhaps they were counting on the fictional droughts caused by warming? I’m not sure. Low crop yields would cause an individual to move from farming to a different line of work, but unless there are food shortages in Mexico(I’m not aware of any.), why do these twits think people would move because a farmer had a bad couple of years? I could go on and on, but it’s back to work for me.
During an ice age I would think Mexico would be a fine place to go. Who would want to go north. Oops, must be another one of those hoax postings by some hoaxing scientists.
Unless we USA taxpayers pay zillions to the hoax God we will be inundated with Mexicans. Are they making threats now?
Alex the skeptic said: So where will Californians migrate to?
Ahhh….that would be the land of Oz.
Q//But his general claims were often a “post-normal science” abomination, and his scientific work (as in the present instance) was sometimes very slipshod.//unQ
call it as was.. Political activism. It has nothing to do with science. Science is merely the new political weapon of choice.
regards
someone posted on an earlier thread louise gray/UK Telegraph piece on the State of the Climate Report, which is now all over the MSM. the Australian manages to bring the Oppenheimer/Mexican “story” into their coverage:
29 July: Australian: AP: Global warming undeniable, say scientists
Compiled by more than 300 scientists from 48 countries, the report said its analysis of 10 indicators that are “clearly and directly related to surface temperatures, all tell the same story: Global warming is undeniable”…
The new report, the 20th in a series, focuses only on global warming and does not specify a cause…
A study by Princeton University researchers released on Monday suggested that continued warming could cause as many as 6.7 million more Mexicans to move to the United States because of drought affecting crops in their country…
http://www.theaustralian.com.au/news/breaking-news/global-warming-undeniable-say-scientists/story-fn3dxity-1225898240544
while Fiona inserts claims humans are causing the warming, even tho the Report states no such thing:
28 July: Financial Times UK: Fiona Harvey:
Peter Stott, of the UK’s Met Office, which contributed to the NOAA report, said the data showed clearly human influence over the climate…
Myles Allen, of Oxford University, said it was clear from the accumulated work of climate scientists that greenhouse gases were the problem. He said: “Climategate never really brought climate science into question at all.”…
http://www.ft.com/cms/s/0/77bc6952-9a7b-11df-87fd-00144feab49a.html
http://michellemalkin.com/2010/07/28/cbs-news-judge-issues-injunction-blocking-parts-of-arizona-law/comment-page-3/#comment-964469
I am sorry but when I first saw this study I saw RED. People are being purposefully run off their farms, starved to death and Dr. Stephen Schneider has the gall to try and link the problem to a few degrees change in temperature when the real cause is KNOWN????
The problem IS NOT temperature it is The World Trade Organization Agreement on Agriculture and NAFTA.
Mexican farmers were driven off the land by international trade agreements not by temperature changes. To actually understand the problem you need to realize all the repercussions of the “free trade” agreements.
Former US president Bill Clinton admits that the US ‘free trade’ policy has forced millions of people in third world countries into poverty and starvation.
“Today’s global food crisis shows we all blew it, including me when I was president, by treating food crops as commodities instead of as a vital right of the world’s poor, Bill Clinton has told a UN gathering.
Clinton took aim at decades of international policymaking by the World Bank, the International Monetary Fund and others, encouraged by the US, that pressured Africans in particular into dropping government subsidies for fertiliser, improved seed and other farm inputs, in economic “structural adjustments” required to win northern aid. Africa’s food self-sufficiency subsequently declined and food imports rose.
“Food is not a commodity like others,” Clinton said. “We should go back to a policy of maximum food self-sufficiency. It is crazy for us to think we can develop countries around the world without increasing their ability to feed themselves.” [November 2008]
In the dozens of countries where the International Monetary Fund (IMF) and World Bank have imposed structural adjustment programs (SAPs), the people who have seen deterioration in their standards of living, reduced access to public services, devastated environments, and plummeting employment prospect
More recently:
I wish I could tell you this was an April Fools joke. I really do.
“About a month ago [April 2010] Bill Clinton sat in congress and admitted that he played a vital part in the willful destruction of the agricultural base of Haiti in order to “relieve them of the burden of producing their own food so they could leap right into the industrial revolution“. Not only does he try to pass off their neoliberalization scheme as a “mistake” but he admits it was really only good for ”some of my farmers (subsidized rice farmers) in Arkansas“….”
Here is the nitty gritty on what has actually happened in Mexico thanks to President Clinton’s attack on wold farming through NAFTA and the World Trade Organizations Agreement on Agriculture.
“According to a study by Jose Romero and Alicia Puyana carried out for the federal government of Mexico, between 1992 and 2002, the number of agricultural households fell an astounding 75% – from 2.3 million to 575, 000…..
The vacuum created by retreat of the Mexican state from agriculture was filled by large US and Mexican agribusiness. In the post-NAFTA period the bulk of FDI in agricultural sector has been in the agri-business and agro-processing rather than agriculture[15]. As a result a few large trans-national agribusiness firms, mostly US and Mexican, dominate storage, flour milling, grain trading[16] and meat processing. Put differently they dominate the intermediation chain that takes crop or cattle and makes it a marketable commodity. Transnational agribusiness has used this dominant position and a process of vertical and horizontal integration to establish an overwhelming presence in the market for wheat, rice, corn, soya, poultry, meat, pork and eggs….
There has been a significant increase in migration out of rural areas as livelihoods are lost and farms have been abandoned. The hope was that this migration out of low-productivity agriculture would be absorbed into higher-productivity non-agrarian urban employment. But anemic employment growth in the post-NAFTA period, particularly in manufacturing[20], put paid to that…..To put this in context between 1994 and 2004, Mexico’s labour force grew by approximately 1 million annually[25]. So effectively today Mexico imports food from the USA and exports farmers and agricultural labour.
It is not just the fact that Mexico’s small and marginal farmers have borne the brunt of the adjustment of Mexican agriculture’s integration into global markets. The spike in food prices in the last couple of years has put enormous pressure on its BOP and the agricultural trade deficit that had begun narrowing has widened sharply,….price increases has meant that import costs of oilseeds, milk, eggs, meat and meat products has increased significantly. At the same time prices for most of Mexico’s agricultural exports such as fruits and vegetables have either stagnated or declined.
In many ways therefore, despite the strides in agricultural exports, Mexico’s NAFTA based transnational agri-business driven agricultural strategy must be deemed a failure. Food production has stagnated, cultivated area under food production has declined and the underinvestment that has characterized Mexican agriculture in the 1980s has not been reversed. The problem of food security has reappeared and because of large migration of farmers and farm labour to USA, depleting the rural countryside of the human resources it requires for an agrarian revival, even if public policy chose to focus on it…
…it is important to remember that 95 percent of the world small and marginal farmers live in poor, developing countries and that 75% of the world’s poor survive on agriculture. For developing countries therefore the key to both food security and livelihood security is the ability to protect small and marginal farmers from unfair competition…[There are] 450 million small and marginal farmers (globally)…” http://www.countercurrents.org/mohanty230608.htm
Other Reading:
Food Security, Farming, CAFTA and the WTO
Undermining Abundance: The Big Business of Creating Scarcity
History, the International HACCP regs and Food
Stolen harvest: the hijacking of the global food supply
Will this Mexican migration be as swift and overwhelming as the migration of those fleeing rising sea levels?
This reminds me of the Dept of Agricultures Plant Zone Maps. Because of global warming, they have been inching up the temp zones a little each year.
Saying things like “soon we’ll be growing palm trees in New York”, “bananas in Cleveland” etc
There are a whole lot of people that are really ticked off after this past winter.
Willis:
RE: Yield
One does not harvest areas that do not grow anything due to drought or flood or other weather conditions such as early snows destroying crops which did grow. However, one does not harvest areas due to other situations such as war, drug wars or any other possibility which may prevent harvest of crops which did grow, that is non – weather related. Tough call as to how to look at the data but it must be considered in the same manner throughout not with different definitions of yield intermittent in the analysis. Total production is the issue but one must know when WEATHER was an issue as opposed to some other factor if we are talking about climate causing migrations of people.
Slightly and knowingly OT:
[snip]
[reply] This is a science blog, and though your post is not unreasonable, it may sidetrack the topic into a non-science controversial area. Sorry. RT-mod
These people are always trying to connect global warming to the latest “issue” – this is a typical technique that propagandists use and an easy way to identify them.
This is not the first time I saw the climate scienits/media spin blame global warming for the results of big Ag aggression.
On October 11, 2009 the Guardian UK published a story titled “Food, famine & climate change: India’s scorched earth” They go on to recount a story of a widow whose husband committed suicide by drinking pesticide. “Suicide is the latest epidemic among farming communities as climate change parches the heart of India, destroying agriculture and plunging the poorest families into crippling debt….” http://www.guardian.co.uk/lifeandstyle/2009/oct/11/food-climate-change-famine-india
Again the story is an out right lie, leaving out the real facts:
The suicides are not a one off caused by a drought in one season.
Farmer suicides in India: “Now the full toll—surely among the largest sustained waves of suicides in human history—is becoming apparent. And as Sainath emphasizes, these numbers still underestimate the disaster, since women farmers are excluded from the official statistics… It is important that the figure of 150,000 farm suicides is a bottom line estimate…. As Professor Nagaraj puts it: “There is likely to be a serious underestimation of suicides…what has driven the huge increase in farm suicides, particularly in the Big Four or ’Suicide SEZ’ States? “Overall,” says Professor Nagaraj, “there exists since the mid-90s, an acute agrarian crisis. That’s across the country. In the Big Four and some other states, specific factors compound the problem…. Cultivation costs have shot up in these high input zones, with some inputs seeing cost hikes of several hundred per cent… Meanwhile, prices have crashed, as in the case of cotton, due to massive U.S.-EU subsidies to their growers. All due to price rigging with the tightening grip of large corporations over the trade in agricultural commodities.” http://alternatives-international.net/article1394.html
http://www.counterpunch.org/sainath02122009.html
As far as I am concerned this is akin to murder. President Clinton, Dan Amstutz (who wrote the agreement) the members of Congress who voted for it, and the climate scientists who are busy hiding the real cause – the rigged “free trade agreements” – are morally responsible.
Willis: good job, as usual.
This is similar to another study, which IIRC, showed that Irish potato production was falling with increased temperatures.
While the potato harvest was declining, the authors did not look at the total harvest, which was increasing. In other words, while potato production had fallen, total food production had increased over the time studied.
My Spanish is not good enough to tell, but are other agriculture products on that site?
I hardly think Mexicans need the weather to inspire a move to the USA. Obama and the courts are doing the job already.
Gail Combs says:
July 28, 2010 at 3:24 pm
Dang Gail, now you’ve got me seeing RED! I knew some of that but….. WOW!
Yeah, we sure do need more government – – don’t we?
“In this particular crisis, government isn’t the solution to the problem, government IS the problem!”
And looking back over the issues cover here, what percentage of the cases is THAT the cause? Far to many….
Sorry. RT-mod
No problem, your right.
This a wonderful piece. The complaints about Schneider’s work becomes really quite lyrical. Oh, by the way, having grown up on a working farm, I can explain the difference between “planted” and “harvested.” Farmers report what they planted because that information goes into the government’s Soil Bank and is relevant for government subsidies. They report what they harvested because you have to harvest a minimum amount to keep your property in the Soil Band subsidy program. The fact that they planted more than they harvested does not say anything about the success of the crops. They might not harvest a field that they planted because prices for that crop fell, because they had made enough on other fields, the truck broke, they decided to sell the crop on the side of a highway, they got bored, a better opportunity presented itself, and many other reasons. In other words, if you know anything about farming, you know that the information under “planted” is totally worthless.
I think Michael Oppenheimer believes that he can appeal to the Tea Partiers by linking global warming to an increased flow of illegal immigrants from third world countries. You can see that politics is not exactly his thing.
You really have to dis-entangle the political and economic forces in Mexico from a simple agriculture-climate relationship to predict emigration. People certainly will follow calories if they are starving, but starvation so often results from repressive governmental policies. Mexico’s social stratification and criminal enterprises also exacerbate the normal stresses of farming. You have to parcel out all the factors to have a hope of saying anything meaningful. If it were the product of a young scholar, this analysis would look suspiciously like resume-padding.
US farming efficiency will put Mexican corn out of business and cause a flood of immigrants way before global warming, in fact this is what is already happening. And GMO pollen won’t help the heirloom varieties either especially if any GMO company were to bring in lawyers to stop seed saving claiming to poor farmers that their seed is the company’s intellectual property after polluting it lol