Rankings were based on the polling of leaders from 12 national environmental  groups. Top presidential  pick received three points, second pick two points, and third pick one point. Total points were tallied to reach the final ranking. 

Presidents Points
1) Theodore Roosevelt (R) 28
2) Richard Nixon (R) 15
3) Jimmy Carter (D) 13
4) Barrack Obama (D) 7
5) Thomas Jefferson (D-R) 3
6) Franklin Delano Roosevelt (D) 2
7) Gerald Ford (R) 2
8) Bill Clinton (D) 1

Only eight of the nation’s 44 Presidents received votes.

Sources:

The Corporate Knights, “America’s Greenest Presidents: Exploring an Environmental Legacy”