U.S. soldiers from the 3rd Cavalry Regiment take part in an artillery exercise on forward operating base Gamberi in the Laghman province of Afghanistan December 24, 2014. (Photo by Lucas Jackson/Reuters)

An Iraqi soldier stands guard as a pipeline burns in the background after an explosion 30 kilometers (20 miles) northeast of Tikrit, Iraq, Monday, February 11, 2008. (Photo by Bassem Daham/AP Photo)

A North Korean soldier kicks a pole along the bank of Yalu River near the North Korean town of Sinuiju, opposite the Chinese border city of Dandong, February 4, 2014. (Photo by Jacky Chen/Reuters)

An Iraqi soldier drives MRAP at his base in Makhmour, after it was freed from control of Islamic State, south of Mosul, April 17, 2016. (Photo by Ahmed Jadallah/Reuters)

A man impersonating North Korean leader Kim Jong Un gestures as he stands before North Korean cheerleaders attending the Unified Korean ice hockey game against Japan during the Pyeongchang 2018 Winter Olympic Games at the Kwandong Hockey Centre in Gangneung on February 14, 2018. (Photo by Yelim Lee/AFP Photo)

South Korea's Shim Sukhee falls in the women's 1,500m short track speed skating heat event during the Pyeongchang 2018 Winter Olympic Games, at the Gangneung Ice Arena in Gangneung on February 17, 2018. (Photo by Mladen Antonov/AFP Photo)

A competitor poses before the Tough Guy Challenge endurance race on January 27, 2013 in Telford, England. Every year thousands of people run the 8 mile assault course which involves freezing temperatures, fire and ice. (Photo by Michael Regan)

A Lion-Tailed macaque holds a big block of ice with a mix of frozen vegetables and fruit at the zoo in Leipzig, central Germany, Friday, July 19, 2013. Weather forecasts predict sunny weather and warm temperatures for Germany in the next few days. (Photo by Jens Meyer/AP Photo)