Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)

A Maasai man in ceremonial dress poses for visitors to take photographs of him in front of one of around a dozen pyres of ivory, in Nairobi National Park, Kenya Thursday, April 28, 2016. The Kenya Wildlife Service (KWS) has stacked 105 tons of ivory consisting of 16,000 tusks, and 1 ton of rhino horn, from stockpiles around the country, in preparation for it to be torched on Saturday to encourage global efforts to help stop the poaching of elephants and rhinos. (Photo by Ben Curtis/AP Photo)

Global wildlife populations will decline by 67% by 2020 unless urgent action is taken to reduce human impact on species and ecosystems, warns the biennial Living Planet Index report from WWF (World Wide Fund for Nature) and ZSL (Zoological Society of London). From elephants to eels, here are some of the wildlife populations most affected by human activity. Here: The maned wolf is among the large mammals in the Brazilian Cerrado that are threatened by the increasing conversion of grasslands into farmland for grazing and growing crops. (Photo by Ben Cranke/Nature Picture Library/Alamy Stock Photo)

A juvenile leopard cat, seized by authorities during an anti-smuggling operation, is seen past suspected smugglers during a press conference announcing the seizure of trafficked exotic animals in Surabaya on March 27, 2019. Indonesian authorities said March 27 they had seized five komodo dragons and dozens of other animals being sold on Facebook, as the country battles to clamp down on the illegal wildlife trade. (Photo by Juni Kriswanto/AFP Photo)

An orphaned giraffe nuzzling a wildlife keeper at Sarara camp in Kenya, one of 70 pictures being sold by Prints for Nature (printsfornature.com) to raise money for work by the Conservation International charity. This giraffe was rehabilitated and returned to the wild, as a number of others have done before him. Right now, giraffe are undergoing what has been referred to as a silent extinction. Current estimates are that giraffe populations across Africa have dropped 40 percent in three decades, plummeting from approximately 155,000 in the late 1980s to under 100,000 today. (Photo by Ami Vitale/National Geographic)

A Sponge Bob Square Pants character is helped up a flight of stairs during the 2013 London Toy Fair at Olympia Exhibition Centre on January 22, 2013 in London, England. The annual fair which is organised by the British Toy and Hobby Association, brings together toy manufacturers and retailers from around the world. (Photo by Dan Kitwood)

Gunfire erupted at a Denver pot celebration Saturday, injuring two people and scattering a crowd of thousands who had gathered for the first 4/20 counterculture holiday since the state legalized marijuana... Photo: A woman smokes a large marijuana joint at the Vancouver Art Gallery during the annual 4/20 day, which promotes the use of marijuana, in Vancouver, British Columbia April 20, 2013. (Photo by Ben Nelms/Reuters)

A British couple drink hot chocolate at Chillout cafe in Dubai May 12, 2013. Chillout, owned by UAE's Sharaf Group, is the first ice lounge in the Middle East, with temperatures set at –6 degrees Celsius (21 degrees Farenheit). The cafe, with its illuminated interiors, curtains, paintings and seating arrangements, is all made of carved ice and frozen sculptures. (Photo by Ahmed Jadallah/Reuters)