alt.global-warming - join
A discussion of the problem of global warming
High activity, 725 subscribers, Usenet

globalchange - join
Moderated discussion of environmental science, economics, policy and politics, especially as related to global change issues such as climate change, biodiversity, and sustainability.
Low activity, 366 members, moderated

sci.environment - join
Discussions about the environment and ecology.
High activity, 1434 subscribers, Usenet