Because trump was terrible for the environment, I'm never going to deny that, Biden needed to undo the damage done before him and make huge steps to protect the environment. He has failed on both.
When we are faced with the possible collapse of all civilization through climate change he could be argued as one of the worst presidents ever cause the longer we go without seriously addressing the cause of climate change the more serious the action needs to be.
Because the status quo at this point will also kill millions, just slower.