People walk during a polluted day in Shenyang, Liaoning province, March 31, 2016. (Photo by Reuters/Stringer)

The northern lights, or aurora borealis, illuminate the sky over Flakstad beach on Lofoten Islands in the Arctic Circle on September 5, 2017. (Photo by Jonathan Nackstrand/AFP Photo)

Ivanka Trump poses with Kristina Hilko, Lauren Shovlin, and Anna Nesbitt, members of the Girls of Steel Robotics initiative, at the Astrobotic Technology facility in Pittsburgh, Pennsylvania on August 14, 2018. (Photo by Jason Cohn/Reuters)

A couple joke as they walk on the beach on August 22, 2018 in Wonsan, North Korea. (Photo by Carl Court/Getty Images)

A tower belonging to the Abengoa solar plant at the Solucar solar park is seen in Sanlucar la Mayor, Spain on October 1, 2018. (Photo by Marcelo del Pozo/Reuters)

The tail of a stranded whale is pictured on the beach of De Haan, Belgium on October 25, 2018. (Photo by Francois Lenoi/Reuters)

A man selling bags of water is seen at a taxi parking bay lined with campaign posters in the district of Lingwala in Kinshasa on December 18, 2018. Democratic Republic of Congo goes to the polls on December 23, 2018 in elections which could see the country emerge from 17 years of conflict-ridden rule under controversial President Joseph Kabila. (Photo by John Wessels/AFP Photo)

Mini-pigs perform during the presentation in Balashikha, Russia on December 19, 2018. (Photo by Maxim Shemetov/Reuters)