helps to prevent potentially fatal hyperthermia due to heat stress. The effectiveness of evaporative cooling depends upon humidity; wet-bulb temperature, or more complex calculated quantities such as wet-bulb globe temperature (WBGT) which also takes account of solar radiation, give a useful indication of the degree of heat stress, and are used by several agencies as the basis for heat stress prevention guidelines. A sustained wet-bulb temperature exceeding is likely to be fatal even to fit and healthy people, unclothed in the shade next to a fan; at this temperature human bodies switch from shedding heat to the environment, to gaining heat from it. In practice, such ideal conditions for humans to cool themselves will not always existhence the high fatality levels in the 2003 European and 2010 Russian heat waves, which saw wet-bulb temperatures no greater than 28 °C. A 2015 study concluded that depending on the extent of future global warming, parts of the world could become uninhabitable due to deadly wet-bulb temperatures. A 2020 study reported cases where a wet-bulb temperature had already occurred, albeit too briefly and in too small a locality to cause fatalities. In 2018, South Carolina implemented new regulations to protect high school students from heat-related emergencies during outdoor activities. Specific guidelines and restrictions are in place for wet-bulb globe temperatures between and ; wet-bulb globe temperatures of or greater require all outdoor activities to be canceled. Heat waves with high humidity On 8 July 2003, Dhahran, Saudi Arabia saw the highest heat index ever recorded at with a temperature of and a dew point. The 2015 Indian heat wave saw wet-bulb temperatures in Andhra Pradesh reach . A similar wet-bulb temperature was reached during the 1995 Chicago heat wave. A heat wave in August 2015 saw temperatures of and a dew point of at Samawah, Iraq, and with a dew point of in Bandar-e Mahshahr, Iran. This implied wet-bulb temperatures of about and respectively. The government urged residents to stay out of the sun and drink plenty of water. Highest recorded wet-bulb temperatures The following locations have recorded wet-bulb temperatures of or higher. Weather stations are typically at airports, so other locations in the city may have experienced higher values. Climate change Study results indicate that limiting global warming to 1.5 °C would prevent most of the tropics from reaching the wet-bulb temperature of the human physiological limit of 35 °C. See also