A large bull walrus returns to the shores of Prins Karl Forland after diving and feeding on clams. (Photo by Paul Nicklen/National Geographic). Svalbard, Norway, 2011

With the United Nations and Tudor City in the foreground, lightning strikes in the sky over the East River as a major storm approaches New York City July 2, 2014. Tropical Storm Arthur, the first of the Atlantic hurricane season, gathered strength July 20, 2014 and would likely reach hurricane strength over the next couple of days. (Photo by Timothy A. Clary/AFP Photo)

A Ugandan soldier, part of the 9,000-strong African Union Mission in Somalia, (AMISOM) walks through the Banadir soccer stadium on August 15, 2011 in Mogadishu, Somalia. The stadium, Somalia's largest soccer facility, had been under control by Islamic extremist Shabab militants for the past two years until they withdrew from the capital more than a week ago. (Photo by John Moore/Getty Images)

Clouds gather as walkers pause atop a ridge in Mountain View, California January 7, 2016. (Photo by Noah Berger/Reuters)

Waves crash against the lighthouse at Newhaven, England, Monday March 28, 2016. Some flights at London's Gatwick and Heathrow airports have been diverted due to high winds battering much of Britain and western France. The high winds from a storm caused 87 cancellations and 43 diversions at Gatwick and Heathrow because flights had trouble landing safely. (Photo by Steve Parsons/PA Wire via AP Photo)

The annual calendar features stunning shots of lighting, cloud formations and the aurora australis. Hundreds of photographers from every Australian state and territory submitted images to the Bureau of Meteorology for selection in the year’s calendar, with only the best chosen to represent the full spectrum of Australian weather. Here: April. A path through the clouds between Townsville and Richmond, Queensland. (Photo by Captain Victoria Harrison/Australian Bureau of Meteorology)

Margaret Morris dancers exercising on the sands at Saint-Idesbald. (Photo by Fox Photos/Getty Images). August 1929

A villager pours brine into troughs at ancient salt fields on May 5, 2005 in Yantian Village on Hainan Island, China. (Photo by China Photos/Getty Images)