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The jet stream and polar vortex on January 3, 2017. Map from the University of Maine Climate Change Institute.
Photo: UCS/Anthony Eyring
USDA-SARE/Edwin Remsberg
Bering Land Bridge National Preserve. Flickr
Image: Flickr/mmatsuura
New York City smog in the 1960's. Photo: Wikimedia
Photo: Rick Obst/CC by 2.0, Flickr
James Finch
USDA
Photo: Ian Swoveland
Image: joel-t/iStock
NOAA/Flickr
