Speaker: Dr. Jonathan Proctor, Post-Doctoral Fellow in Harvard University Center for the Environment

Title: “Non-linear effect of atmospheric opacity on global crop yield"

Abstract: Humans have a history and a potentially intensified future of altering the global optical environment through air pollution, climate change and geoengineering. Yet the agricultural impacts of these manipulations remain highly uncertain due to potentially offsetting losses of total insolation and gains of diffuse insolation. While theory suggests that crop yields may have a concave response to changes in light from an increasingly opaque atmosphere, such a non-linear effect has never been empirically estimated. Here, I leverage year-to-year variation in growing season cloud optical thickness as a natural experiment to provide the first non-linear empirical estimates of how increased atmospheric opacity alters the quantity and quality of sunlight at the Earth's surface and how this, in turn, impacts maize and soy yields in the United States, Europe, Brazil and China. I find that the sunlight-mediated impact of cloud scattering and absorption on yields is consistent and non-linear across crops and regions. Mechanistically, I find that the concavity in the sunlight-mediated effect of clouds on yields is driven by concavity in the response to total sunlight in some regions and by benefits from diffuse light, i.e. the "diffuse fertilization effect," in others. Applying these empirical estimates to earth system model simulations of air pollution and climate change, I find that anthropogenic changes in the quantity and quality of sunlight due to changes in clouds may have economically substantial impacts on yields.

GSPD comprises scientific talks up to one hour in length by graduate students and post docs, but all are welcome to attend, including faculty and staff. Lunch will be provided. Please bring reusable plates and cutlery to reduce waste.