December 1 — William Temple Hornaday Born (1937)
December 2 — International Whaling Commission Created (1946)
December 3 — Ellen Swallow Richards, Pioneering Environmental Chemist, Born (1842)
December 4 — Eastern Steller Sea Lion De-listed (2013)
December 6 — Eliot Porter Born (1901)
December 7 — Beijing Issues First Red Alert for Air Pollution (2015)
December 8 — American Bird Banding Association Formed (1909)
December 9 — Wupatki National Monument Created (1924)
December 10 — Olivier Messiaen Born (1908)
December 11 — International Mountain Day
December 12 — Paris Climate Agreement Adopted (2015)
December 13 — Baiji Porpoise Declared Extinct (2006)
December 14 — World Monkey Day
December 15 — Chico Mendes Born (1944)
December 16 — Carol Browner, 8th EPA Administrator, Born (1955)
December 17 — Alexander Agassiz, Pioneering Oceanographer, Born (1835)
December 18 — First Commercial Nuclear Energy Produced (1957)
December 19 — Richard Leakey, Kenyan Conservationist, Born (1944)
December 20 — Earliest Date for Winter Solstice
December 20 — “It’s A Wonderful Life” Released (1946)
December 21 — Dr. Robert Bullard, Father of Environmental Justice, Born (1946)
December 21 — Trevor Kincaid Born (1872)
December 22 — Ruth Yeoh, Malaysian Environmentalist, Born (1982)
December 22 — Lady Bird Johnson, Environmental First Lady, Born (1912)
December 23 — Times Beach, Missouri, Declared Uninhabitable (1982)
December 24 — The Christmas Tree
December 25 — European Rabbits Introduced to Australia (1859)
December 26 — UN Convention to Combat Desertification Began (1996)
December 27 — Second Voyage of the Beagle Began (1831)
December 28 — Endangered Species Act Enacted (1973)
December 29 — Convention on Biological Diversity Began (1993)
December 30 — Six Geese A-Laying
December 31 — John Denver, Singer-Songwriter and Conservationist, Born (1943)