Person:

Rigden, Angela

Temperature and humidity directly influence milk yields, suggesting that climate change may pose a fundamental challenge to maintaining the high productivity of US dairy systems. However, the sensitivity of the dairy sector to weather variability remains uncertain; although animal-level responses are well-described, housing and other management practices (e.g., fans and sprinklers) can moderate the influence of weather exposure on productivity. Here we assess the influence of historical variation in the Temperature and Humidity Index (THI) on milk yields in the US using monthly, state-level yield data and high-resolution daily weather data from 1981 to 2018. We find that milk yields are compromised by exposure to both extreme heat (> 79 THI) and cold (<39 THI), causing average daily yield decreases of around 3.7% and 6.1%, respectively. Colder regions are more sensitive to heat extremes, and warm regions are more sensitive to cold extremes. Sensitivity to THI has reduced dramatically over time, presumably due to substantial changes in farm management. Climate trends contributed modestly to rising yields in most states via alleviating cold stress, although more extreme future conditions may negate these benefits. Our results highlight the importance of farm management for mediating climate change impacts.