Global risk to livestock of heat stress under climate change

Abstract:

Nearly 40% of all agricultural output in developed countries comes from livestock, and many of the world's billion poorest people rely on livestock for their livelihoods. The impacts of excess heat on livestock production already cost over $2B annually in the United States alone. While the direct threat of heat stress on humans under climate change has received considerable research attention, no comprehensive global studies exist for livestock. Using a systematic review, we synthesized multiple temperature-humidity indices (THIs) for estimating heat stress in livestock related to production, fertility and mortality impacts. We map the published THI and impact relationships out globally, highlighting the relative paucity of studies in developing countries and for non-dairy livestock. We utilize bias-corrected (quantile mapping) CMIP6 climate model projections for daily maximum temperature and relative humidity and spatially explicit stocking densities (FAO) to calculate THI conditions for major livestock groups (cows, pigs, chickens) globally under different climate and socio-economic development pathways. Results show that mean global warming of greater than 4°C above pre-industrial levels causes many regions of the world to experience dangerous or extreme THI conditions for livestock for over 200 days per year by the end of the century. In addition, livestock expansion is projected to coincide with some of the most at-risk regions in the tropics. Specifically, socio-economic development pathways with high greenhouse gas emissions, low environmental protections or accelerated growth more than double deadly heat risk exposure for livestock in the Middle East, Africa, and Latin America based on livestock number increases alone. This research highlights the need for more studies on the direct effects of heat stress on all species of livestock, especially in developing countries.