Another Michael Oppenheimer FAIL – 2010 claim on Mexican 'climate refugees' evaporates once his paper is corrected.

Michael Oppenheimer is the Albert G. Milbank Professor of Geosciences and International Affairs in the Woodrow Wilson School and the Department of Geosciences at Princeton University.

WUWT readers may recall a recent essay titled ‘What global warming really looks like’ – Michael Oppenheimer FAIL where I pointed out the desperate and ridiculous claims by Michael Oppenheimer to try to link the recent Colorado forest fires to global warming climate change climate disruption. He did a miserable job with his claims, and the data from the National Interagency Fire Center didn’t support his claims at all.

It seems Mr. Oppenheimer is again in the news, this time being smacked down due to another example of some shonky science where he and two other Princeton researchers tried to prove that imagined climate driven crop issues in Mexico were creating climate refugees. Here’s the Princeton press release from July 26, 2010.  It immediately became a darling story of climate media bloviators from the BBC to Scientific American to Yale 360 who wrote:

Rising temperatures and reduced crop yields in Mexico could force as many as 6.7 million Mexicans to emigrate to the United States over the next 70 years, according to a new study. Researchers from Princeton University, led by atmospheric scientist Michael Oppenheimer, made that projection after studying historical patterns of emigration, climate change, and crop yields in Mexico between 1995 and 2005. Oppenheimer and his colleagues concluded that for every 10 percent reduction in crop yield, an additional 2 percent of Mexicans aged 15 to 65 could emigrate to the United States.

Well, it turns out Oppenheimer’s paper is complete junk, and when the error is corrected by less excitable researchers without an agenda, they find no evidence of a causal link.

Here’s the paper that started it all: 

Linkages among climate change, crop yields and Mexico–US cross-border migration (Full PDF here)

Shuaizhang Fenga, Alan B. Kruegera, and Michael Oppenheimer

Edited* by Stephen H. Schneider, Stanford University, Stanford, CA, and approved June 24, 2010 (received for review March 3, 2010)

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 ofemigration to the United States.

The estimated semielasticity of emigration with respect to crop yields is approximately −0.2, i.e., a 10% reduction in crop yields would lead an additional2%of the population toemigrate. We then use the estimated semielasticity to explore the potential magnitude

of future emigration. 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.


And here’s the rebuttal paper:

Unobserved time effects confound the identification of climate change impacts (Full PDF here)

Maximilian Auffhammera, and Jeffrey R. Vincent

A recent study by Feng et al. [Feng S, Krueger A, Oppenheimer M (2010) Proc Natl Acad Sci USA 107:14257–14262] in PNAS reported statistical evidence of a weather-driven causal effect of crop yields on human migration from Mexico to the United States. We show that this conclusion is based on a different statistical model than the one stated in the paper. When we correct for this mistake, there is no evidence of a causal link.


After the model in the work by Feng et al. (1) is correctly estimated using their data, the statistical evidence suggesting a causal relationship between weather-driven crop yields and emigration from Mexico to the United States disappears. The statistical evidence in the work by Feng et al. (1) is based on an incompletely controlled before-and-after comparison of emigration rates and crop yields across states. Any omitted factor

positively (negatively) correlated with yields and negatively (positively) correlated with emigration rates over time affecting all states confounds this estimated effect. The results in the work by Feng et al. (1), therefore, cannot be given a causal interpretation,because a variety of factors changed during this period. According to the work by Feng et al. (1), these factors included “the effect of NAFTA, the Peso crisis, and changes in US border controls such as increased border enforcement after 2001” (ref. 1, p. 14258); regarding the second factor, after 1994, “the Peso depreciated considerably against the US dollar, doubling the real wage rate earned by emigrants” (1). The work by Feng et al. (1) also points to the “reform of the land tenure system and the opening of Mexico’s economy

through liberalized trade and deregulation of markets” (1), which further impoverished small farmers and rural landholders.

These factors would confound a pure before/after comparison, and therefore, they make it absolutely essential to control for them through time effects. Results from correct estimation of the model suggest that, for the sample used in the work by Feng et al. (1), these factors, and not weather, were responsible for the change in emigration rates between the two periods.

As Sheldon Cooper would say: “Bazinga!”

Dr. Roger Pielke Jr. Sliced this paper up when it first came out, calling it “silly science”. He wrote on Jul27, 2010:


A new paper is out in a journal getting a reputation for silly science that predicts that climate change will lead to a massive influx of Mexicans across the border to the United States. Here is how the LA Times breathlessly opened its news story on the PNAS paper:

Climbing temperatures are expected to raise sea levels and increase droughts, floods, heat waves and wildfires.

Now, scientists are predicting another consequence of climate change: mass migration to the United States.

Between 1.4 million and 6.7 million Mexicans could migrate to the U.S. by 2080 as climate change reduces crop yields and agricultural production in Mexico, according to a study published online this week in the Proceedings of the National Academy of Sciences. The number could amount to 10% of the current population of Mexicans ages 15 to 65.

A reporter emailed me an embargoed copy last week asking for my reactions. Here is how I responded (and I pulled no punches):

To be blunt, the paper is guesswork piled on top of “what ifs” built on a foundation of tenuous assumptions. The authors seem to want to have things both ways — they readily acknowledge the many and important limitations of their study, but then go on to assert that “it is nevertheless instructive to predict future migrant flows for Mexico using the estimates at hand to assess the possible magnitude of climate change–related emigration.” It can’t be both — if the paper has many important limitations, then this means that that it is not particularly instructive. With respect to predicting immigration in 2080 (!), admitting limitations is no serious flaw.

To use this paper as a prediction of anything would be a mistake. It is a tentative sensitivity study of the effects of one variable on another, where the relationship between the two is itself questionable but more importantly, dependent upon many other far more important factors. The authors admit this when they write, “It is important to note that our projections should be interpreted in a ceteris paribus manner, as many other factors besides climate could potentially influence migration from Mexico to the United States.” but then right after they assert, “Our projections are informative,nevertheless, in quantifying the potential magnitude of impacts of climate change on out-migration.” It is almost as if the paper is written to be misinterpreted.


I wonder if we’ll see this in Retraction Watch soon. It sure deserves to be retracted. This is truly junk climate science.

[UPDATE] I trust that Anthony will not object to my pointing out that I posted an extensive rebuttal of Oppenheimer’s nonsense, entitled “Border Transgressions“, no less than two years ago when it first came out in 2010. As a result, I am overjoyed that my views have been upheld. I’m also proud that WUWT, as usual, was on the case from the start.


UPDATE2: Apologies to Willis for my oversight in not including his excellent essay. I believe this one was published directly prior to our change of authorship rules, and somehow I missed it.  – Anthony


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Consider that since a federal court ruled that the irrigation water must be cut off to portions of the Central Valley of California, farmers have been moving to Mexico where they can obtain water. I would be willing to bet that the actually agricultural output of Mexico has been increasing as the output of California has been in decline.

…regarding the second factor, after 1994, “the Peso depreciated considerably against the US dollar, doubling the real wage rate earned by emigrants”…
Did Paul Krugman get a nod in their paper?

charles nelson

Given the ‘right on’, caring, politically correct posture of most Warmists I am always slightly incredulous when they press the ‘race’ button like Oppenheimer did in his paper. It’s a subliminal message of fear and it preys on people’s worst instincts.
It’s almost as if they’re saying “not worried about Global Warming?…well you darn well will be when all those Mexicans start flooding across the border.”
In Europe the influx of racial menace caused by Global Warming will come from ‘sub-saharan’ Africa.
In Australia I’ve heard fears being expressed about climate refugees from sinking Pacific Islands.
And of course let’s not forget the pernicious, “wait till those Indians and Chinese start burning fossil fuels and consuming raw materials the way we do, then the world will really be in trouble.”
But has anyone else ever noticed that any time one questions the Warmist faith they often roll their eyes, adopt that strained saintly posture and claim the moral high ground?
Bizarre I call it.


If Mr Oppenheimer hadn’t been so blinded by his Belief in AGW… he would have been more skeptical of his modeling and would have spotted his silly mistake…. Instead he jumped out his bathtub and went running naked down the street yelling. Eureka!….. Well sir. You may borrow my coat to go home with…;-)

Quite literally, these people are obsessed with proving that ‘climate change’ causes everything. Well, it probably does, but not the way that Oppenheimer et al would imagine. Not only is this material the stuff of stultification and drudgery, it’s just plain boring! These people actually WRITE THIS STUFF DOWN!! Holy cow.


An now back to the real world. We have to be sceptical of such tripe. Let’s looks at what the past and the present tells us during the warming period and the “hottest decade on the record!” Head for the hills!!!!!
Where are the 50 million climate refugees? 😉 LOL
Net migration from Mexico falls to zero – now looks like a net flow back to Mexico!!

50 million climate refugees. We’ve been asking where the bodies are, and they ain’t at the Mexican border any longer. (They turned back 2 years ago after reading Willis’ smackdown)


The trouble is that this is not science this is advocacy and that sense its worked , it made headlines , its entered the mythology and that is what it needed to do . There is virtual no chance that those agencies that ran with this story will go back to it and report it was wrong , therefore for many the memory is of the initial BS claim .
Think about how PR and marketing work , that today’s news is tomorrows waste paper , drop the idea of science and they you will understated why its was a ‘success ‘

Brian H

Mexicans are fleeing CA’s collapse. The liberals collapsed CA to please the migrants. Lesson: you can’t fix stupid.


Pierre found a conference call recording involving Oppenheimer and two other alarmists dictating latest alarmist conjecture to listening journalists, probably to prime the media pump.
audio. Each one of the three delivers a 5 minute alarmist speech, then the listening journos can ask for more. In the latter part are some of the juiciest quotes.


Let’s throw in a few spanners into the works of Mexican climate alarmism.

June 8, 1999
….many forecasters predict that slowing fertility rates will mean that the country’s population will virtually stop growing by 2045.
The tremendous reduction in fertility, from 7 children per woman in 1965 to 2.5 today,…
Apr 22nd 2010
Mexico’s birth rate, once among the world’s highest, is in free-fall.

Gary Hladik

“I trust that Anthony will not object to my pointing out that I posted an extensive rebuttal of Oppenheimer’s nonsense, entitled “Border Transgressions“, no less than two years ago when it first came out in 2010.”
Checking that article, I noticed that NAFTA was mentioned early on in the comments, anticipating one of the points in the current rebuttal paper.

P. Solar

I would have though the primary reason for wanting to migrate from Mexico (to anywhere else, not just USA) is the possibility of being shot in the street or waking up to find one’s head missing.
A few percent less crop yeild is likely well down the list.

Old woman of the north

If somebody did a serious study of the effect of population growth on resources and environment and rejected the reference to ‘climate change’ it would be refreshing. Of course the environment is suffering but it is population pressure that is the issue and it could be dealt with directly instead of wasting billions on trying to stop natural events.
I wait anxiously.

Kelvin Vaughan

Global warming has caused millions of Eastern Europeans to emigrate to the UK!
They come for work building wind farms and fitting solar panels to rooves.

Nice thing about making predictions far out in the future is that no one will remember that you made the silly prediction when the time comes and you can get all the press you want when you make the prediction.

Jim Turner

Could it be that some scientists are more interested in press releases on the back of research papers than in the papers themselves? Do rebuttals get press releases too – and if so, are they picked up?


The “researchers” were working against their own purposes anyway. They were viewing immigration as a problem! Not smart!
Big government and big corporations love infinite immigration. Enriches the rich, starves the poor, lowers wages, causes disruption and confusion, destroys culture. Perfect for the Establishment, thus perfect for paid “scientists” who are the most fashionable and status-conscious people in the world.

There was a time not long ago when common sense studies like this one would not have been news.

Mindert Eiting

Mike Bromley the Kurd says:
July 13, 2012 at 12:58 am
Quite literally, these people are obsessed with proving that ‘climate change’ causes everything. Well, it probably does, but not the way that Oppenheimer et al would imagine. Not only is this material the stuff of stultification and drudgery, it’s just plain boring! These people actually WRITE THIS STUFF DOWN!! Holy cow.
Probably? It certainly does because of logic: a false theory implies everything, true or false, it does not matter.


Sorry, but that paper can’t be trusted any more than any other supposed ‘science’ paper. How can you trust a paper that’s published in PNAS? That’s a warmist publication, like Science and Nature and all those other supposed ‘science’ journals. Anyway – why on earth would people want to move away just because they can’t grow anything? So some people call a lot of sunny days a ‘drought’ (that’s just to scare decent folk). Everyone here knows that a warmer world is a better world. As for moving away from floods – that’s ludicrous. Water is essential for life, just like CO2 is food for plants.
Only the other day there was an article here about how no scientist can be trusted because they are only in it for the money. This is probably just masquerading as ‘peer review’. I bet it is manufactured controversy just to get more people to buy the journal and make the scientists big bucks. It’s not science. This is the only place that publishes good science – you can tell that by all the hits. Disappointing that you’ve used a ‘science journal’ as a filler between the otherwise excellent blog science articles, like how it’s perfectly natural that so much of the USA has been so hot lately and how the melting sea ice in the Arctic is not at all abnormal.
More blog science please. Stay away from the ‘peer reviewed’ nonsense – it gives it too much credibility.
REPLY: Dear anonymous coward, you forgot to add /sarc at the end. Nobody is forcing you to visit or read. – Anthony

Gail Combs

The only thing that has cause mass migration of Mexicans to the USA is NAFTA, dreamed up by Bush senior and signed by President Clinton. However politicians NEVER EVER want to take the blame for all their failed policies that harmed the poor and middle class while helping their rich buddies.
NAFTA was just a repeat of Scotland’s land clearances only this time aimed at the Mexicans with the same predicted effect – migration of the population.

….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[19].
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. And what little employment there has been has largely been in the informal sector. As a result there has been a change in the pattern of rural out-migration. In the 1980s the likelihood of migrating to urban Mexico was higher than that of migrating to the USA. Today, as a result of anemic employment growth, the likelihood of migrating to the USA is significantly higher[21].
The World Bank estimates that between 2000-05, 400,000 Mexicans migrated to the USA annually[22]. According to other estimates this number is closer to 500,000[23]. 300,000 of these are from rural Mexico and again mostly small, marginal farmers and agricultural labour[24]. 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 seems Economics and Politics is always left out of these ‘chicken little’ CAGW causes everything pronouncements. No wonder politicians LOVE CAGW it is even better than Bush as a political scapegoat.


Another reason why there won’t be any climate refugees – everyone knows that we will adapt to climate ‘disruption’. You don’t see all the US farmers moving to Canada just because the weather has been a little bit warm and dry these past few months. They use their initiative and get drought declared so they can tide over till El Nino arrives later this year. Those that don’t adapt – well it’s survival of the fittest, just as it’s always been.


30 years of shame.

James McCown

Emigration from Mexico can be explained with one word: Socialism.


When does this type of science start to degrade the reputations of Princeton and the publishing journals?

Not clear… is this piece Willis Eschenbach’s? Looks like Anthony’s style.
Willis, it would be good to clarify up top. But whoever wrote it, thanks.
REPLY: It is mine, Willis always has a bold guest post added at top – Anthony

“We show that this conclusion is based on a different statistical model than the one stated in the paper. When we correct for this mistake, there is no evidence of a causal link.”
As such, the original Oppenheimer 2010 paper should be withdrawn. It does not show what it say it shows. It contains a significant error.


Oppenheimer spend much of his career full-time with the Environmental Defense Fund, a radical activist group, before making the move to academia. He is a clear example of a fusion of activist and sciency agendas masquerading as “research”…. No surprise, he is also a leading figure in the IPCC process for AR5:
Michael Oppenheimer is a radical activist
“Oppenheimer joined the Princeton faculty after more than two decades with The Environmental Defense Fund (EDF), a non-governmental, environmental organization, where he served as chief scientist and manager of the Climate and Air Program. He continues to serve as a science advisor to EDF.
“Oppenheimer is a long-time participant in the Intergovernmental Panel on Climate Change (IPCC) which won the Nobel Peace Prize in 2007, serving recently as a lead author of the IPCC’s Fourth Assessment Report and now as a coordinating lead author of the Fifth Assessment Report, as well as, a special report on climate extremes and disasters….”

Rob Potter

Nice catch Jimbo (July 13, 2012 at 1:53 am).
The whole misanthropic, Malthusian, “Limits to growth” crowd have been refuted by the real world data that you have pointed out – birth rates drop as people get richer! Getting people out of poverty is best way to reduce population growth rates, not limitations to growth.

Chris B

Maybe the UN could force Mexico to produce biofuels in order to make the prediction happen. They need a win, desperately.

Pamela Gray

Hansen is to blame for this kind of sloppy statistical gymnastics. It’s called “scenario application proposals”, SAP for short, and clearly is the favored (cough-cough) statistical offspring of post-modern climate scenario application proposal scientists, known as SAPS…er…AGW scientists, bent on living off the funds made available to those willing to examine the various scenarios of a falling sky.
I am a bit surprised that the requisite ABC formula was not followed in Mike’s first attempt at this immigration scenario. However, I am sure Mike’s rebuttal to the rebuttal will include his variable controlled ABC scenarios. The saps’ stories just aren’t complete without it ya know.
And just to fine grain the point, this type of research (SAPs) really are just stories, not discussions of facts and observations.

The whole CAGW meme is based on fear and based on scientific ignorance which is a result of the current school system. It is also fueled by activists like Oppenheimer who has this deep compassionate trusting voice of mid west doomsday preacher.

David Ball

More proof of the problems within the universities. Political agendas becoming more important than doing quality research. Systemic bias has corrupted higher (read all) education.

Gary Pearse

How can an honest man hold a chair in Geosciences (a sad diminutive of the no-BS-and- respected-term “Geology”) and Public Policy?

Pamela Gray

“Appropriately” educated people can be just as stupidly duped as those who cannot read or write their own name. And “appropriately” educated people can be just as willing to dupe the populace as those who cannot read or write their own name. The current school system has nothing to do with it. Fear and greed are not born in the current school system but are found in the hearts and souls of any generation, regardless of their education. You can, and with every generation, fool most of the people, most of the time, from pre-historic man, to the modern masses.


Oppenheimer has been at this since the 1980s, and has never been anything but a medicine-show barker for AGW. He is the exact opposite of dedicated scientist who follows the truth where it leads him. He is a stain on the integrity and reputation of a fine university and the alumni at Princeton should demand his removal and replacement by a scientist who practices real science.
The original paper in question exploits racial fears and the immigration issue for political purposes and that is why it was published. It might as well have been headlined, “AGW Causes Catastrophic Explosion of Illegal Immigration.”


I swear I just read where Paul Bain asserted that this stuff can only be reliably discussed between scientists and we mortals have no place in the discussion, and here we have competing reports between scientists that shows low levels of competence and a tendency to MSU (make stuff up). And oddly enough this was debunked in the blogosphere long ago.
If plotted, the number of recent refudiated papers from lettered SAPS (thank you, Pamela) would form a hockey stick.

But, but, but… Mexico’s agricultural productivity has been increasing for 20 years or more, both total and per acre!
Oppy posits a cause-and-effect where the cause does not exist. We can’t say whether he’s right or not because Mex ag prod has gone up not down.
It turns out that Mexico’s ag sector is booming along quite nicely thank you.
And it turns out that glooooball waaaarming is GOOD FOR AGRICULTURE.
That’s right. Warmer Is Better. More food grows in warm climes than in cold ones. The growing seasons are longer and the plants grow faster, too.
Assuming that many of you readers are not farmers, it may interest you to know that most of your food is grown in the SUMMER when it’s hot rather than the winter when it’s cold.
That’s a biological factoid. Plants like it warm. There is no place on Earth too warm for growing plants except boiling hotsprings and fresh lava. Too dry maybe but not too warm.
The most productive ag spot in the USA is Imperial Valley, south of Death Valley and not far from Mexico. The warmest place is also the best ag land! Are you surprised?
We know this truth to be self-evident: Warmer Is Better for agriculture.

Pamela Gray

They don’t call em hot house tomatoes just because it sounds cool, or rather hot. Up the temp and humidity and suddenly you green up the globe. And I do mean suddenly. Another example: The weeds of Jamaica’s hot humid climate adorn our greenhouses as spoiled kings and queens of sought after ornamentals. What we spend great sums of money on and then coddle and baby with loads of additional money on growlamps, humidifiers, soil amendments, and fertilizer grow faster than a population of ferral cats in Jamaica. I’ve been from Mo Bay to Kingston along the coast road. One can hardly run off the road with the bumper pads of vegetation thickets so tightly constraining the concrete roadway.

Louis Hooffstetter

Another non-science paper that lacks testable data. Conclusions: “When there are food shortages, people migrate to where the food is”, and “Climate change “could…”, “may…” cause this to happen in Mexico, “depending…”, on “estimated…, extrapolated…, blah, blah, blah”. Brilliant deductions. This is definitely Nobel Peace Prize material.
Of all of the potential factors influencing migration (politics, birth rate, imperceptible climate change, racism, pogroms, spirit of adventure, economics, etc.), imperceptible climate change apparently has the greatest effect. Despite the fact that warmer, wetter climates + higher CO2 levels = more food in the form of plant growth.


I’ve linked this before but for those who haven’t seen it, it bears reading. Oppenheimer is one of those we have to blame for the IPCC:


Equating climate as a “forcer” to immigration while ignoring base economics sounds vaguely familiar to a CAGW theory I have seen somewhere…..


Mr. Oppenheimer is bringing the reputation of Princeton into disrepute and damaging their brand. If I were an alumni, or a member of their board of regents, I would indeed be concerned.


But… But it was peer reviewed… By non-citizen scientists and everything…

Lucy Skywalker says:
July 13, 2012 at 5:49 am
> Not clear… is this piece Willis Eschenbach’s? Looks like Anthony’s style.
That confused me too, but I eventually concluded that Willis added the first update to Anthony’s post as opposed to Willis adding the first update to his post.
Perhaps when a post is updated, the source of the update is clear, or more to the point, when a post or update is finished, the bottom has a signature to show it’s the bottom. Then we’d see post … -Anthony [Update] … w.; instead of the post … [Update] … w. that confused us.
In any event, it’s impressive that Pielke Jr, Willis, and other WUWT denizens quickly came up with some of the points listed in the new paper. Perhaps I should check the credits there! 🙂

David, UK

Wouldn’t that 2-10% just be lost in the noise of the other 50 million climate ‘fugees?
Oh wait…


‘So, how do we get all these evil, racist, right-wing deniers to get with the CAGW program?’
‘That’s it! They’re racists! Everyone knows they hate Mexicans more than they hate Warmists!
Just convince them global warming will also cause immigration! They’ll be installing solar panels in no time!

“Up the temp and humidity and suddenly you green up the globe. ”
Don’t forget upping that building block of the biosphere , CO2 , too .
BTW : anybody around CO in Aug , Check out my MidSummer 2012 party invite . I live in a “pre-evacuation” zone west of the Rampart Range fire which destroyed 300 homes down in Colorado Springs . A week later we had cloud bursts . the pix of our watering hole at the time of the fire and a week ago . Climate change !


Paging Stephen Schneider. Torment us again about advocacy and truth.