Here is a list prominent figures - writers, philosophers, scientists, activists, politician, professionals, citizens, explorers, organizers, opponents - in environmental history and ethics. You might want to consider these, and others as possible topics for option D of the term paper.

Edward Abbey - writer
Ansel Adams - photographer, Sierra Club leader
Jane Addams - Chicago settlement house worker & urban activist
Homero Aridjis - Mexican organizer of Grupo de los Cien
John James Audubon - pioneering bird artist
Mary Hunter Austin - writer & opponent of Western water projects
Rachel E. Bagby - community activist
John H. Baker - leader of national Audubon Society
Gregory Bateson - pioneer systems thinker
Daniel Beard, WWU geography alum, reformist commissioner of US Bur. Rec., Audubon VP
Willaim Beebe
Wendell Berry - writer, farmer
Henry Beston - writer
Gertrude Blom - defender of the Lacandon & the Chiapas rainforest
Murray Bookchin - philosopher, founder of social ecology
Norman Borlaug - architect of the agricultural "Green Revolution"
Randy Borman, Ecuadoran activist
Irving Brant - conservationist in FDR administration
William Brewster - pioneer ornithologist and conservationist
Harvey Broome - The Wilderness Society founder, planner
David Brower - Sierra Club, Friends of the Earth, Earth Island Institute leader
Lester Brown - founder of Worldwatch Institute
Carol Browner - Head of EPA under Clinton
Gro Brundtland - Prime Minister of Norway & Chair of World Commission on Env. & Development
John Borroughs - 19th Century nature writer
Helen Callicott - physician, author, anti-nuclear activist
Arthur Carhart - early wilderness advocate, landscape architect
Rachel Carson - scientist, author of Silent Spring
Jimmy Carter - environmentalist president
Frank Chapman - early Audubon Society leader
William Colby - long-time Sierra Club leader
Thomas Cole - 19th C. American landscape painter
Barry Commoner - activist environmental scientist
Anne Conway - 17th Century philosopher of monistic vitalism
Hugo Conwentz - founder of early german environmental NGO
Jacques Cousteau - oceanographer & filmmaker
Lisa Crawford - Ohio activist
Chuck Cushman - anti-environmental activist
Herman Daly - pioneering ecological economist
Mary Daly -ecofeminist theologian
Ding Darling - founder of National Wildlife Federation
Bernard DeVoto - crusading writer
Will Dilg - founder and leader of Isaac Walton League
Floyd Dominy - ambitious Commissioner of Bureau of Reclamation, 1959-69
Marjory Stoneman Douglas - crusader for the Everglades
William O. Douglas - conservationist and Supreme Court Justice
Rasalie Edge - Audubon Society critic, leading conservationist in 1930's
Loren Eiseley - writer
Ralph Waldo Emerson - American philosopher, author of "Nature"
Paul Ehrlich - scientist, population activist
Dave Foreman - founder of Earth First!
Dian Fossey - Gorilla biologist and defender
BirutŽ Galdikas - Orangutan biologist and defender
John Gallagher - Ohio Audubon activist and educator
Neftali Garcia - founder the environmental movement in Puerto Rico
Lois Gibbs - Love Canal activist, founder Citizens Clearinghouse for Hazardous Waste
Jane Goodall - Chimpanzee researcher and advocate
Elizabeth Dodson Gray -ecofeminist theologian
William B. Greeley - Forest Service chief, timber industry leader
George Bird Grinnell - editor, national park advocate, wildlife conservationist
Emily Haig - Washington writer, activist in Sierra Club, Audubon, The Nature Conservancy
Roderick Haig-Brown - fisherman / conservationist
Alice Hamilton - physician and researcher/advocate against industrial diseases & toxins
Garrett Hardin - human ecologist & provocative ethicist
Hazel Henderson - environmental economist
William T. Hornaday - wildlife conservationist
Harold Ickes - Secretary of Interior for FDR
Henry M. Jackson - Washington State Senator, author of NEPA and North Cascades NP legislation
Hazel Johnson - S. Chicago community activist
Robert Underwood Johnson - magazine editory, ally of John Muir
Florence Kelly - Progressive union organizer and workplace activist, Chicago
Petra Kelly - founder of German Green party
Barbara Kerr - inventor of the solar box cooker
Vasil Krutilla - environmental economist
Winona LaDuke - Annishinabe environmental activist
Frances Moore Lappe - nutritionist
Aldo Leopold - writer, ecologist, moral philosopher
Walter Lowdermilk - hydrologist & soil conservationist
Wangari Maathai - biologist and founder of Kenya's Green Belt Movement
Thomas Malthus - English economist
Alice Tepper Marlin - founder of Council on Economic Priorities
George Perkins Marsh - pioneer of human ecology
Robert Marshall - wilderness advocate, benefactor and founder of The Wilderness Society
Stephen T. Mather - founding director of the National Park Service
Margaret McDowell - Chicago sanitation activist
Chico Mendez, Brazilian rubber tapper organizer and rainforest activist
Carolyn Merchant - environmental historian
Bertha Mosely - fought use of arsenic in tobacco fields of Virginia
John Muir - preservationist, founder of the Sierra Club
Margaret Murie - writer, conservationist
Olaus Murie - wildlife biologist, leader of The Wilderness Society
Edmund Muskie - US Senator
Arne Naess - seminal ethicist & philosopher of deep ecology
Helen & Scott Nearing - Maine/Vermont activists & exemplars of back-to-land movement
Richard Neuhaus - pastor, critic of environmentalists' ignoring of social problems
Margaret Morse Nice - ornithologist
Richard Nixon - President who supported major env. legislation of 1970's
Helena Norberg-Hodge - sustainable development in Ladakh
Margaret Norse Nice - ornithologist & ethologist
Sithembiso Nyoni - activist for woment & env. issues in Zimbabwe
Frederick Law Olmsted - pioneering park advocate and landscape architect
Sigurd Olson - writer, parks and wilderness leader
Lorrie Otto, Wisc. Audubon activist, natural landscaping pioneer
Medha Patkar, Indian activist
Katharine Payne - whale and elephant bioacoustics researcher
Roger Tory Peterson - wildlife artist and conservationist
Gifford Pinchot - first American forester, conservation advisor to T. Roosevelt, first Chief of USFS
John Wesley Powell - 19th Century scientist, bureaucrat and visionary
Dixy Lee Ray - head of Atomic Energy Commission, governor of Wash., critic of environmentalists
Tom Regan - philospher of animal rights
Franklin D. Roosevelt - President and proponent of government conservation
Theodore Roosevelt - great conservation President
Henry S. Salt - English humane activist & biographer of Thoreau
Ken Saro-Wiwa, Nigerian activist
Sue Savage-Rumbaugh - primate langauge researcher, and advocate for Bonobos
Floyd Schmoe - Washington (Mt. Raineer esp.) naturalist and mountaineer
Ellen Churchill Semple - geographer of human-nature systems
Ernest Thompson Seton - North country writer
Vandana Shiva - physicist & environmentalist
Karen Silkwood - antinuclear whistleblower
Julian Simon - resource economist, critic of environmentalism
Peter Singer - ethicist of animal liberation
Jan Christian Smuts - politician and philosopher of holism
Henry Spira, American animal rights activist
Starhawk - spiritual ecofeminist
Carol Von Strom - community activist
Maurice Stong - Canadian organizer of UN Environment Conferences
Wilma Subra - chemist and activist involved in Louisiana's "Cancer Alley" area
Ellen Richards (Swallow) - scientist of pollution, industrial chemistry, nutrition; brought word "ecology" to America
David Suzuki - env. scientist and activist
Luisah Teish -ecofeminist
Henry David Thoreau - author, philosopher, creator of wilderness idea in American culture
John & Nancy Todd - ecological engineers and founders of New Alchemy Institute
Stewart Udall - Interior Secretary in Kennedy & Johnson administrations
Ann Underwood White - geographer of African development
Edward O. Wilson - biologist, crusader for conservation of biodiversity
Hazel Wolf - labor & Seattle Audubon activist
Mabel Osgood Wright - nature writer & photographer, founder of Conn. Audubon
Robert Sterling Yard - founder of both National Parks Association and The Wilderness Society
Howard Zahniser - originator of the Wilderness Act of 1964

Some additional names:
Sir Frank Fraser Darling, Mabel Loomis Todd, Perrine Moncrieff, Myles Dunphy, Katherine Wiley, Maurice Goddard