Climate Change, Crop Yields, and Internal Migration in the United States

Abstract

We investigate the influence of weather anomalies on net migration in the Eastern United States using a county-level panel for the period from 1970 to 2009. One major mechanism is through the effect of weather on agricultural yields, which we examine in further detail using an instrumental variables approach. Our preferred model uses the seasonality of the sensitivity of corn yields to extreme heat over the growing season, which peaks during corn flowering, as instrument. The reduced-form estimate of the migration response to extreme heat closely mirrors the seasonality of corn yield. Our IV approach will provide an unbiased estimate of the responsiveness of outmigration to yield unless other determinants of migration, such as peoples direct preference for weather, perfectly align with the pattern of corn flowering. This is unlikely given that the exact dates of corn flowering vary from year to year. Our estimated semi-elasticity ranges from -0.3 to -0.4 depending on the chosen time trend, i.e., a one percent change in yields leads to an opposite 0.3-0.4 percentage point change in the net migration rate. The migration response is strongest for young adults and not significant for senior citizens. Extrapolating from this relationship, we project that climate change would induce significant outmigration in the U.S. Corn Belt.

Nonlinear permanent migration response to climatic variations but minimal response to disasters

“…The turning point value is at ∼2.2 m of average annual precipitation, which suggests that below the period-average annual precipitation of 2.2 m, any increase in rainfall reduces outmigration, but above it, any increase in rainfall increases outmigration such that with a rise in precipitation from 2.3 m to 3.3 m for example, a household's annual migration probability goes up by 0.00146. The effect, however, is much smaller compared with the effect of temperature on migration, which is consistent with previous findings that even agriculture-related outmigration is mostly sensitive to temperature rather than precipitation (15).…”

“…A rising temperature could therefore increase outmigration through a negative effect on income in agriculture as well as nonagricultural sectors and potentially over time by creating a less stable social environment. Prior work suggests there is evidence that temperature affects migration through its influence on agricultural productivity (13)(14)(15).…”

“…In another study using baseline climate in 1960-1989 and the expected change in weather, by 2070-2099, 5-y outmigration rates of rural counties in the US Corn Belt are projected to increase by 30% due to decline in crop yields as a consequence of warming climate (15). Although these results provide some basis of comparison for our study, the magnitude of the effects of temperature on migration may vary by location due to a host of unobservable characteristics in different country settings that cannot be fully controlled for.…”

What Do We Learn from the Weather? The New Climate-Economy Literature

“…Boustan, Kahn and Rhode (2012) find similar outmigration in their study of the long-run impact of tornadoes in the United States during the 1920s and 1930s. Feng, Oppenheimer, and Schlenker (2012) document qualitatively similar patterns in a more recent period , suggesting that outmigration from areas experiencing negative agricultural productivity shocks still occurs today, particularly for young adults.…”

Natural Disasters and Human Mobility

“…Munshi (2003) showed that a decrease in rainfall in Mexico leads to more emigration to the US. Using country level panel data from 1970 to , Feng et al (2012 show a negative relationship between countries level outmigration and crop yields in the Corn-Belt in the US. More precisely, they find that a 1 % decline in crop yields due to weather shocks increase the migration of the adult population by 0.17%.…”