A woman smokes marijuana during the annual 4/20 marijuana rally on Parliament Hill in Ottawa, Ontario, Canada, April 20, 2017. (Photo by Chris Wattie/Reuters)

A park ranger stands next to a nothern white female rhinoceros named Najin at Ol Pejeta Conservancy, some 290 kms north of the Kenyan capital, Nairobi, on January 27, 2015. Najin is one of only five members of the sub-species left on the planet, three of which reside at Ol Pejeta Conservancy. Conservationists and scientists met in Kenya this week to come up with a last ditch plan to save the northern white rhinoceros from extinction. (Photo by Tony Karumba/AFP Photo)

A performer wearing costumes walk on stilts before a show during a lantern fair at the beginning of Chinese Lunar New Year, in Xi'an, Shaanxi province, February 11, 2016. (Photo by Reuters/Stringer)

A sunflower “smiles” in a field in Tokyo on August 7, 2014. Some 20,000 sunflowers were enjoyed by visitors to the area this week. (Photo by Yoshikazu Tsuno/AFP Photo)

A mine detection rat is given banana as a reward after successfully identifying an inactive mine on July 2, 2015 in Siem Reap, Cambodia. The Cambodian Mine Action Center (CMAC) working with the Belgian NGO APOPO has recently begun testing the feasability of using large mine detection rats from Tanzania to help clear fields of mines and unexploded ordnance in one of the most bombed and mined countries in the world. (Photo by Taylor Weidman/Getty Images)

Members of the Gafatar sect walk in the rain as they evacuate their compound, which was later burned down by local villagers, in Antibar village, Mempawah Regency, Indonesia West Kalimantan Province, January 19, 2016 in this photo taken by Antara Foto. Local authorities and police moved the sect members to an army barracks located some 70 km (43 miles) away from Antibar for their safety following recent disputes between the sect and the villagers, Antara said on Tuesday. (Photo by Jessica Helena Wuysang/Reuters/Antara Foto)

Young Christian Lebanese women, who are members of Kataeb Phalangist party, show their skill in handling arms while they train in a village between Christian-controlled eastern port of Jounieh and the Christian village of Zahle in the west Lebanon on September 9, 1976. The Lebanese civil war erupted in April 1975. (Photo by Erich Stering/AFP Photo)

Rare images of wild tigers in Bhutan, captured by camera traps, show tigers and other animals using high-altitude wildlife corridors which are lifelines to isolated tiger populations and critical to genetic diversity, conservation and growth. Here: A wild Bengal tiger (Panthera tigris tigris) captured on a camera trap in corridor eight at an altitude of 3,540 metres in Trongsa, Bhutan. (Photo by Emmanuel Rondeau/WWF UK/The Guardian)