The Center for Biological Diversity Action Fund has conducted an in-depth review of the remaining Democratic Presidential candidates, focusing on “four key environmental issue areas: saving wildlife, protecting public lands, ensuring environmental justice and ending the climate crisis”. Their scorecard appears above.
Regarding which candidates were considered:
We evaluated every candidate polling above 1% in the latest national polls. We did not evaluate former New York City Mayor Michael Bloomberg because of his decision not to participate in any Democratic debate, build a grassroots network of supporters or compete in any of the early state caucuses or primaries.
Their analysis is thorough and too long to copy here with this many candidates. So here is the relevant link to their website. Their findings are concisely presented, organized by candidate, with footnotes, so it makes for an easy but highly informative read.
If you care about the environment and want to know where the candidates stand on these vital issues then this is the best review I have yet seen.