A commuter gestures to Boris Johnson as he rides across Vauxhall Bridge in London, England on November 19, 2015. The London mayor was opening a cycle superhighway. (Photo by John Stillwell/PA Wire)

In this Thursday, December 1, 2016 photo, Cat Bigney, part of the Oglala Native American tribe, waits on the shore of the Cannonball river for travelers to arrive by canoe at the Oceti Sakowin camp where people have gathered to protest the Dakota Access oil pipeline in Cannon Ball, N.D. So far, those at the camp have shrugged off the heavy snow, icy winds and frigid temperatures. But if they defy next week's government deadline to abandon the camp, demonstrators know the real deep freeze lies ahead. Life-threatening wind chills and towering snow drifts could mean the greatest challenge is simple survival. (Photo by David Goldman/AP Photo)

Vendors selling marigold garlands, which are used to decorate temples and homes during the Hindu festival of Durga Puja, drink tea as they wait for customers at a wholesale flower market in Kolkata, India October 6, 2016. (Photo by Rupak De Chowdhuri/Reuters)

Girls sits on a bench during summer at the Central Park in New York, United States, 2011. (Photo by An Rong Xu)

8-year-old Fulani boy Suleiman Yusuf drinks milk from a cow belonging to his father cattle near his family's house at Kachia Grazing Reserve, Kaduna State, Nigeria, on April 16, 2019. Kachia Grazing Reserve is an area set aside for the use of Fulani pastoralist and it is intended to be the foci of livestock development. The purpose for the grazing reserves is the settlement of nomadic pastoralists and inducement to sedentarisation through the provision of land for grazing and permanent water as way to avoid conflict. (Photo by Luis Tato/AFP Photo)

The Clavie, a burning barrel packed with tar soaked sticks fixed on the top of a pole, is surrounded by people at the Doorie Hill on January 11, 2018 in Burghead, Scotland. People welcome in the New Year with the fire ceremony which has ancient roots dating back to the 1750s, when the Julian calendar was reformed in Britain. It is believed to bring good luck for the coming year. (Photo by Jeff J. Mitchell/Getty Images)

An Afghan hound arrives for the second day of the Crufts Dog Show in Birmingham, Britain March 9, 2018. The annual four-day event sees around 22,000 pedigree dogs visit the centre, before the “Best in Show” is awarded on the final day. (Photo by Darren Staples/Reuters)

A female Kurdistan Workers Party (PKK) fighter stands near a security position in Sinjar, March 13, 2015. Women fighters at a Kurdistan Workers Party (PKK) base on Mount Sinjar in northwest Iraq, just like their male counterparts, have to be ready for action at any time. Smoke from the front line, marking their battle against Islamic State, which launched an assault on northern Iraq last summer, is visible from the base. Many of the women have cut links with their families back home; the fighters come from all corners of the Kurdish region. (Photo by Asmaa Waguih /Reuters)