Dan Copeland, left, and Alex Morneau of Biddeford, Maine, former high school cheerleaders, perform back flips while enjoying the record breaking heat, Thursday, May 18, 2017, at Old Orchard Beach, Maine. The temperature climbed well into the 90s in many locations throughout the state. (Photo by Robert F. Bukaty/AP Photo)

Two hippopotamus are fed with pumpkins at the Hanoi Zoo, in Hanoi, Vietnam, 25 October 2018. The zoo has been the home for more than 800 animals of over 90 different species, including three hippopotamus, since it was built in 1976. (Photo by Luong Thai Linh/EPA/EFE)

In this November 26, 2018 photo, men run during 100 meters athletics competition of the second edition of the Panamanian indigenous games in Piriati, Panama. These games were held in the Embera town of Piriati, some 55 miles (90 kilometers) east of Panama City. (Photo by Arnulfo Franco/AP Photo)

Fisherwomen laying barrels with salt in preparation for herring curing, 1937. (Photo by Topical Press Agency)

Second World War veteran 90 year old William Walker launches the Scottish Poppy Appeal, together with soldiers from the Royal Highland Fusiliers, 2nd Battalion the Royal Regiment of Scotland, on October 27, 2011 in Penicuick, Scotland. Mr Walker, who was wounded while serving in Burma in 1943 with the Royal Scots, helped the soldiers form the shape of ninety to celebrate the 90th anniversary of the annual November campaign. (Photo by Jeff J Mitchell/Getty Images)

A man watches the huge waves which brakes at the Paseo Nuevo's promenade in San Sebastian, Basque Country, Spain on 11 January 2016 where the wind has reached to 90 km/h and have been registred waves of eight kilometres due to the bad weather. (Photo by Juan Herrero/EPA)

A pilot inflates his balloon before the 37th International Hot Air Balloon Week in Chateau-d'Oex, January 24, 2015. According to the organizers, over 80 balloons from 20 countries are participating in the ballooning event in the Swiss mountain resort. (Photo by Pierre Albouy/Reuters)