Resource: Professional Societies
- Cinematographers XX
- Citizens' Climate Lobby
- Clean Air Council
- Clean Ocean Access
- ClientEarth
- Climate Justice Alliance
- Climate Reality Project
- Climate Reality Project
- Climate Science & Policy Watch
- Climate Science Alliance
- Climate Science Legal Defense Fund
- ClimateLinks
- Coastal & Estuarine Research Federation
- Coastal & Estuarine Research Federation
- Coastal Research and Education Society of Long Island
- Coastal Studies Institute
- Code2040
- Colorado Department of Natural Resources
- Colorado Department of Public Health & Environment
- ColorCreative
- Committee on Women in Science, Engineering and Medicine
- Committee to Protect Journalists
- Communities for a Better Environment
- Confédération Mondiale des Activités Subaquatique
- Connecticut Department of Energy and Environmental Protection
- Conservación ConCiencia
- Conservancy of Southwest Florida
- Conservation International
- Conservation Law Foundation
- Conservation Strategy Fund
- Consortium for Ocean Leadership
- Cool Effect
- Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder
- Coral Reef Alliance
- Coral Reef Conservation Program
- Coral Restoration Foundation
- Cornell Institute of Biotechnology
- Council for the Advancement of Science Writing
- Council of Science Editors
- CR8:BLK
- CRC 235 Emergence of Life
- Cultural Survival
- Daguerreian Society
- Dallas Film
- Dallas Underwater Photographic Society
- Dark Noise Collective
- De-Canon: A Visibility Project
- Deaf Poets Society
- Deep Sea Conservation Coalition
- Deep South Center for Environmental Justice