I spent some time researching a lot of different environmental agencies. I checked all the agencies on multiple charity rating sites. Below are the ones that rose to the top out of a much larger list! That said, this list is not exhaustive. If you have any to add that you’ve researched & found to be good, please add them in the comments.
Sierra Club http://www.sierraclub.org/ National, great ratings, founded in 1892, excellent track record. I like this one because America is such a huge polluter that donating to a national organization seems very important.
Union of Concerned Scientists http://www.ucsusa.org/ International, great ratings, “scientists and engineers develop and implement innovative, practical solutions to some of our planet’s most pressing problems”
Earthworks https://www.earthworksaction.org/ International, great ratings, “dedicated to protecting communities and the environment from the adverse impacts of mineral and energy development while promoting sustainable solutions”
Natural Resources Defense Council https://www.nrdc.org/ International “works to safeguard the earth – its people, its plants and animals, and the natural systems on which all life depends.” Love that they have a focus on environmental justice. This org was not accredited on BBB Wise Giving but it has been getting a ton of press and was highly rated on a number of other rating guides.
ACLU National, great ratings. This is a civil rights org but I can’t recommend them enough – “worked to defend and preserve the individual rights and liberties guaranteed by the Constitution and laws of the United States.”
For donating: if you can, do a reoccurring donation, even $5 a month helps. Consistent monthly donations organizations plan their budgets. If you don’t have the money – giving your time is arguably MORE impactful. Reach out to them to find out what you can do locally.
Check the effectiveness of most charities at these sites:
BBB Wise Giving Alliance http://www.give.org/
https://www.charitywatch.org/top-rated-charities (needs membership after viewing a few)