The past four years have been the warmest on record. According to Climate Central, 198 cities have had an increase in the annual number of days reaching over 90 degrees. This has serious adverse effects on outdoor sports. Extreme temperatures can slow down the body's natural cooling mechanism, increasing risk of heat stroke and heat exhaustion. In July, the New York Triathlon was canceled due to extreme heat. 64 football players have died from heat stroke since 1995.