Early Life Exposures to Temperature Extremes and Health at Birth

This paper contributes to an emerging literature that seeks to understand and quantify the costs of climate change on developing countries and, in particular, on vulnerable subpopulations within those countries. Climate change induces higher frequency of tail weather events such as days of extreme temperatures (heat waves and arctic vortices), precipitation (flooding and drought), and windstorm variation (hurricanes), and exposure to these events at various stages of the lifecycle has been shown to have implications for health, human capital accumulation, labor productivity, economic growth and other outcomes.

In this paper, we investigate the effects of prenatal exposure to extreme temperatures and its effects on birth outcomes in the context of China. We focus both on outcome variables; in particular, birth weight and size at gestational age, that have been explored by the existing literature in other settings, as well as one that, to our knowledge, has yet to be examined; i.e., birth defects.

There is now a substantial body of work suggesting that early life or in utero exposure to extreme temperatures potentially has strong impacts on health both in terms of (short-run) birth as well as later life outcomes. Overall, the literature concludes that the welfare costs of early exposure to extreme temperatures to both the individual and society are sizeable. However, the literature on the infant health impact of climate change has had to grapple with a number of issues regarding data quality (e.g. lack of large, high quality, and representative data sets), model specifications (e.g. heterogeneity and the asymmetric/nonlinear impact of heat waves versus extreme cold, lack of adequate controls for environmental and other confounders, differential impact on males and females), and, especially, identification (technological “adaptation” through indoor heating and AC and residential sorting).

We exploit a large data set in China, and, more importantly, a set of context-specific institutional features that are particular to China to address some of the identification issues described above. Based on the matched dataset of birth records and daily prenatal temperature exposure, we find a linear relationship between birth weight and temperature, where extremely cold days are associated with a decrease in birth weight.

In particular, an additional day with a mean temperature above 85°F, relative to a day in the 45-65°F range, leads to a decline in the probability of low birth weight by 0.032 percent, and a day with a mean temperature below 25°F is associated with an increase in birth weight by 0.047 percent. A key new finding in this paper is on the impact of extreme temperatures on birth defects. Birth defect and temperature are negatively related. Low temperature leads to a significant increase in the probability of birth defect by 0.043 percent while exposure to hot days is associated with a statistically significant decline in the probability of birth defect by 0.061 percent relative to the reference temperature category. Those patterns are similar across three trimesters during pregnancy. Additionally, the findings about temperature exposure and birth outcomes are more pronounced for females.