A simulated casualty is evacuated during an emergency services exercise at the disused Aldwych underground station on February 22, 2012 in London, England. Operation Forward Defensive aims to test the response to a terrorist incident on the London Underground network during the 2012 Olympic Games. (Photo by Peter Macdiarmid/Getty Images)

NASA's DHC-3 Otter plane flies in Operation IceBridge-Alaska surveys of mountain glaciers in Alaska in this image released on September 18, 2014. Over the past few decades, average global temperatures have been on the rise, and this warming is happening two to three times faster in the Arctic. (Photo by Chris Larsen/Reuters/NASA/University of Alaska-Fairbanks)

Double tornadoes, lightning storms and rotating supercells – this is what it's like to chase storms for a year. These dramatic images show apocalyptic weather throughout 2014 from a lightning storm to a pair of rainbows. Roger Hill, 57, has been chasing storms in the United States for thirty years and runs a tour operation with his wife Caryn. Here: a hailstorm rolls over fields, on July 22, 2014, in South Dakota. (Photo by Roger Hill/Barcroft Media)

A flight deck crew prepares to launch a F18 Super Hornet from the deck of the USS Eisenhower off the coast of Virginia, December 10, 2015 in the Atlantic Ocean. US Defense Secretary Ash Carter visited the carrier with India's Minister of Defense Manohar Parrikar to demonstrate US Navy aircraft carrier flight operations. (Photo by Mark Wilson/Getty Images)

An Iraqi special forces Counter Terrorism Service (CTS) member screams during a battle against Islamic State group jihadists (IS) in Mosul's al-Rifaq neighbourhood on January 8, 2017, as an ongoing military operation against the militants continues. Elite Iraqi forces battling the Islamic State group in eastern Mosul reached the Tigris River that splits the city in two for the first time, a spokesman said. (Photo by Dimitar Dilkoff/AFP Photo)

A boy carries a dog as he stands after a Peruvian police operation to destroy illegal gold mining camps in a zone known as Mega 14, in the southern Amazon region of Madre de Dios July 14, 2015. Peruvian police razed dozens of illegal gold mining camps at the edge of an Amazonian nature reserve this week, part of a renewed bid to halt the spread of wildcatting in a remote rainforest region. (Photo by Janine Costa/Reuters)

A seal playfully tries to bite the camera, taken on February 2016 in Plettenberg Bay, South Africa. A group of friendly seals get up close and personal with the camera. The pod of brown fur seals, also known as “cape fur seals”, were shot in Plettenberg Bay in South Africa by dive tour operator Rainer Schimpf. The playful creatures prove they are not camera shy in the slightest as they they swim upside down, grin widely and attempt to bite the camera lens. (Photo by Rainer Schimpf/Barcroft Media)

A gold prospector is detained by agents of Brazil’s environmental agency on the Uraricoera River during an operation against illegal gold mining on indigenous land, in the heart of the Amazon rainforest, in Roraima state, Brazil April 15, 2016. At over 9.5 million hectares, the Yanomami territory is twice the size of Switzerland and home to around 27,000 indians. The land has legally belonged to the Yanomami since 1992, but illegal miners continue to plague the area, sawing down trees and poisoning rivers with mercury in their lust for gold. (Photo by Bruno Kelly/Reuters)