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Wolfram Schlenker, visiting professor at L’X, discusses climate change effects on agricultural yields, asylum applications and pollution

Thanks to the Alliance Partnership, École Polytechnique welcomed visiting Professor Wolfram Schlenker from Columbia University during the spring 2020 semester. He agreed to tell us more about his research projects and results. He also stressed that he was impressed with the quality of the students he met at L’X.

Le professeur Wolfram Schlenker

Wolfram Schlenker

Professor, School of International and Public Affairs (SIPA) and The Earth Institute

Co-director, Center for Environmental Economics and Policy (ceep.columbia.edu)

Co-director, Energy & Environment Concentration at SIPA

You have studied the effect of weather and climate on agricultural yields and how climate trends and the US biofuel mandate influence agricultural commodity prices. What have been your key findings?

I am an environmental economist by training. The primary focus of my studies has been on empirically estimating the benefits and/or cost of environmental regulation by applying econometric techniques to micro-level data. During my graduate studies, there was an active debate about whether global warming will be beneficial or harmful for agriculture in moderate-temperate zones like the United States. My initial work examined the effects of a warming world on agricultural yields. My co-authors and I found that yields increase in temperature until about 29°C for corn, 30°C for soybeans and 33°C for cotton, but that temperatures above these thresholds quickly become very harmful, and the slope of the decline above the optimum is an order of magnitude steeper than the incline below it. Previous studies average temperatures over a season, month, or day and thereby dilute this highly non-linear relationship. The stability of the estimated relationship across regions, crops, and time suggests it may be transferable to other crops and countries.

While agriculture constitutes a small fraction of GDP, it arguably constitutes a large part of consumer surplus as agricultural demand is highly inelastic. As the United States produces 23% of the world calories in the four basic commodities (maize, rice, soybeans, and wheat), which together account for 75% of the calories the world consumes, any impact in the United States will have large repercussions on world markets and welfare. The tripling of commodity prices between 2005 and 2008 reduced consumer surplus from the four basic commodities by approximately 1.25 trillion annually. This has led to renewed interest in the fundamentals of agricultural markets: how will yield shortfall impact commodity prices and how will farmers respond, e.g. by increasing the growing area? Similarly, what are the implications of demand increases due to population growth, or a shift to calorie-intensive diets, e.g. meat rather than vegetables, or biofuel mandates on commodity price and farmer responses? We find that they mainly respond to the extensive margin by expanding the growing area, which in turn will lead to significant CO2 emission from deforestation.

You have also worked on the consequences of weather changes on people mobility or their health due to air pollution…

Agricultural impacts also have large ripple-effects: in a follow-up study, we linked temperature shocks over the agricultural growing area and season in all non-OECD countries to asylum applications to the European Union. We find a significant U-shaped relationship: when temperatures are too low (or high), more people ask for asylum in the EU compared to a year when temperatures are at the moderate optimum.  We only compare a country to itself, i.e., how do asylum applications change if temperatures deviate from the average in a country. Moreover, a higher fraction of the applications is accepted in the following two years.

Weather is an important input into the agricultural sector, yet subsequent research of mine has shown that other environmental conditions still have large direct effects on human well-being.  While a relationship between pollution and health is often documented, it is difficult to establish whether it is causal or spurious (e.g., because poorer people live in more polluted areas and they are sicker for other reasons beyond pollution). A co-author and I exploit the fact that airports generate a tremendous amount of local ambient air pollution on a given day, with areas downwind of an airport experiencing much larger changes in ambient air pollution relative to areas upwind. We leverage the quasi-experimental variation in both airport activity (as mediated through network delays) and wind direction to estimate the causal effect of air pollution on contemporaneous health. Intuitively, if New York City has a snowstorm, Los Angeles Airport, which is several thousand kilometres away, sees an increase in congestion the same day, as well as an increase in pollution in downwind areas.  We find that especially carbon monoxide leads to an increase in hospitalization for respiratory diseases and heart attacks.

Do you think, the current pandemic crisis is directly linked to the topics you investigate? What shall we learn from the current situation and which are the most important results and conclusions you would to like to impart to the public? How do you see the evolution of Higher Education & Research amid the Coronavirus pandemics?

 I do not directly work on infectious diseases or COVID more specifically.  The one takeaway for me though is that it shows us how difficult it is to achieve international cooperation when the benefits mostly accrue to others.  This has implications for other areas, e.g., climate change that primarily benefit future generations, yet the cost of mitigation measures is born by the current generation.  If people struggle to put on a face mask, which has been shown to especially help the spread of the virus to other people while giving some limited protection to the mask wearer combined with some possible discomfort, how will we achieve the required significant costly CO2 reductions?