More than 700,000 Americans were without power on Sunday evening, and about 6 million across the US were at risk for extreme weather, according to CNN. The outages were concentrated in the south-eastern US, where there were severe thunderstorms in the Ohio valley as well as Arkansas, Tennessee and Mississippi. There was a suspected tornado in Bargersville, Indiana, just south of Indianapolis. There were also reports of large hail in northern Kentucky and southern Indiana. At least half of the US population has faced an extreme weather alert since 1 May, according to the Union of Concerned Scientists (UCS), which has been tracking the alerts sent by the National Weather Service. About one in 10 of the alerts have a clear signal linking them to the climate crisis, Juan Declet-Barreto, a senior social scientist for climate vulnerability at UCS, told the Guardian earlier this month. Scientists have established a clear link between the climate crisis and extreme weather events. Last weekend, about 100,000 residents in Shreveport, Louisiana, lost power because of storms that hit the Texas panhandle and moved into Louisiana. The crisis left them facing extreme temperatures as high as 107 degrees without electricity to power air conditioning and other methods of cooling down. Roughly 50 million Americans, including people living in Arizona, Texas, Louisiana, Oklahoma, New Mexico, Arkansas, Mississippi and Tennessee, faced heat alerts Sunday. The high temperatures are expected to continue into the Fourth of July holiday weekend. A heat dome has settled over Mexico and parts of the US south-west. The heat dome is caused by hot ocean air that becomes trapped in the atmosphere. An average of 702 heat-related deaths occur each year, according to the US Centers for Disease Control and Prevention. Temperatures in Texas soared above 100 degrees and contributed to the deaths of a man and his stepson who were hiking in Big Bend national park. Temperatures were around 119F (48C) and the stepson fell ill while hiking. The father died in a car accident while searching for help. Amid those searing temperatures, the Texas governor, Greg Abbott, signed a new law last week that will block Austin and Dallas from implementing measures that would require construction workers to get a 10-minute water break every four hours.