The Daily Mislead

Today, young bunnies, we have a fine example of the Daily Mislead at work. Shuaizhang Feng, Alan Krueger and Michael Oppenheimer have published an estimate of climate change driven migration from Mexico to the US in this century

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. 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 additional 2% of the population to emigrate. 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.

From Climate Depot comes word of an amazing full court press against Michael Oppenheimer from the usual suspects.

Propagandist Michael Oppenheimer shredded: 'There are only 6.3m agricultural workers in Mexico. For Oppenheimer to predict that they will all move north seems preposterous' omichael@princeton.edu

Mark wants you to write to Mike (what is it with these clowns and their Mike mania, Michael Mann, Michael Tobis and now Michael Oppenheimer), and tell him how wrong he is. Mark has some problems with number too. Current estimates are that there are already about 6 million Mexicans in the US without permission, and, Oppenheim's estimate of climate driven migration would be 1.4 to 6.3 million. There are probably about 30 million dual nationals, visa holders and first or second generation descendants of Mexican citizens in the US. But on to the food fight . . .

UN IPCC Lead Author Richard Tol: Oppenheimer's 'silly PNAS paper makes 3 mistakes. 1st: It confuses decadal weather variability with climate change...'
'2nd, it fails to control for other determinants of migration that may well be correlated with weather during the sample. 3rd they extrapolate beyond belief'

Prof. Pielke Jr. Mocks Oppenheimer's 'Silly Science': Immigration paper 'is guesswork piled on top of 'what ifs' built on a foundation of tenuous assumptions'

including this goodie from Ethon's lunch time friend Lubos

Physicist mocks Oppenheimer: 'The descendants of Oppenheimer should sue Oppenheimer and prevent him from using and contaminating the name of their ancestor - and the good name of physics' visit site

So the big bird flew over there to see why Motl was defending a dead, left wing physicist, and read

He and his friends essentially claim that global warming is going to be the main reason of the Mexican illegal immigration. Between 1.4 and 6.7 million Mexicans will arrive to the U.S. by 2080 because their agriculture will get worse, and so on. Of course, this statement is completely preposterous but the media make it even worse when they exclusively quote the upper "6.7 million" figure in the title.

Why is this not going to be a problem, some, not Ethon, might ask? and, of course, the friendly poly-arithmetic (he knows how to add, but not multiply) Motl replies

The number of Mexicans who actually move because of the temperatures may be counted in thousands, not millions. If you check an encyclopedia, the daily temperatures in Mexico City go from 6 to 21 °C in January to 12 to 26 °C in May (the figures are average lows and average highs in the months). In average, there's no excessive heat over there. And the agriculture is not getting worse because of the climate change.

You may check that e.g. Sao Paolo in Brazil, the agricultural powerhouse of Latin America, has temperatures by about 6 °C higher than Mexico City. They're even higher in Rio de Janeiro. Warmth is surely not a problem.

Which makes sense if you don't have a clue about the geography of Mexico. Mexico City sits way high on a plateau. High enough that low landers need a LOT of time to acclimate, and, as even Lubos knows, temperature decreases with altitude. Eli, being a RTFR kinda bunny, went and found a climatic map of Mexico

Guess where Mexico City is. Oh yeah, that large green area down in the south. The yellow part is mostly highlands. The rest of the country is a lot hotter. Lubos, of course, picked the coolest part of Mexico. Why is Eli not surprised?

Oh yes, read the article. Tol and Pielke Jr. have not.