Sharafkhaneh port and lake Urmia. Masoud Ghadiri (Iran). The summer Milky Way is very prominent in this photo. On the galaxy zone, Saturn is located besides the Lagoon nebula. On the right of the horizon, you can see the extreme light pollution of Urmia, which is caused by ever-increasing city development. (Photo by Masoud Ghadiri/National Maritime Museum)

A woman wearing a scarf to cover her face looks on as she waits for a passenger bus on a smoggy morning in New Delhi, India, November 8, 2017. The Great Smog of Delhi is an ongoing severe air-pollution event in New Delhi and adjoining areas in the National Capital Territory of India, in November 2017. Air pollution at this time peaked on both PM 2.5 and PM 10 levels. It has been reported as one of the worst levels of air quality in Delhi since 1999. (Photo by Saumya Khandelwal/Reuters)

Bicycles of various bike-sharing services are seen at an urban village in smog during a polluted day in Shanghai, 2017. Rapid expansion of shared bicycle companies across China has led to massive piles of abandoned bikes as supply outstrips demand. (Photo by Aly Song/Reuters)

A women wearing a mask to protect from extreme smog visits the Tiananmen Gate in Beijing December 8, 2015 as China's capital issues its first ever "red alert" for pollution. (Photo by Damir Sagolj/Reuters)

An airplane is silhouetted at sunrise, seen from the suburb of Saint-Cloud, near Paris, France, 08 December 2016. Paris is undergoing a third day pollution spike, prompting the city to limit vehicle circulation. (Photo by Ian Langsdon/EPA)

Iraqi teenagers swim in waste water from the nearby Tuweitha nuclear facility near Baghdad, Iraq on May 28, 2003. Iraqis are consuming contaminated water unaware of the dangerous pollutants that can cause severe ill health. (Photo by Damir Sagolj/Reuters)

Waves crash over lava as it flows into the ocean near Volcanoes National Park in Kalapana, Hawaii on November 27, 2012. A volcano on Hawaii's largest island is spilling lava into the ocean, creating a rare and spectacular fusion of steam and waves that officials said on Tuesday could attract thrill seeking visitors if it continues. (Photo by Hugh Gentry/Reuters)

Rockhopper penguins live up to their name as they navigate the rugged coastline of Marion Island in the southern Indian Ocean. (Photo by Thomas P. Peschak)