Heat Stress Risk for Summer Olympics in a Warming Climate

As global temperatures rise due to climate change, heat stress will pose an increasing threat to human health and performance. Because athletes exercising outdoors are especially vulnerable to such heat stress, major athletic events, such as the summer Olympic Games, will thus increasingly contend with conditions adverse to the health and performance of athletes. Here we investigated how heat stress risk may affect the eligibility of potential future summer Olympics host cities from a climate and subsequent human heat strain perspective. Using high-resolution temperature and relative humidity data from observations over a historical period (1983-2016) and projections for the mid-21st century, we quantified the probability of heat stress conditions occurring for different sports during the boreal summer (June – October) in 880 potential Olympic host cities, including nine past host cities, in accordance with Sports Medicine Australia's 2021 Extreme Heat Policy. We explored which cities may not be viable to host future summer Olympics due to high probabilities of “extreme heat risk” conditions that require suspension of sports play. For the nine past summer Olympic Games that took place during the historical period, there was up to a 20% probability of extreme heat risk conditions occurring. Over the same historical period, 534 cities out of 880 possible hosts experienced climates with <20% occurrence of extreme heat risk conditions. In mid-21st century projections, only 396 cities fall under 20% probability of extreme risk conditions, a 26% decrease in the number of viable Olympic host cities. Three broad geographic patterns also emerge: there is a latitudinal gradient in the degree of future risk in the Northern Hemisphere; risk is lower in the Southern Hemisphere relative to the Northern Hemisphere; and risk is lower at high elevations. These patterns may offer some strategies for future summer Olympics host city selection, and highlight growing inequity in where the summer Olympics can feasibly be held in the future. Broadly, climate and heat stress risk should be an increasingly important consideration in the host city selection process for future summer Olympics.