with means because in this sentence➡️an explanation of the worry it means the climate change，you are right！

'it' is a pronoun and it is a substitute for 'climate change'. 'with' means 'accompanying' or 'going with'. "Climate change is always a worry, and going with/accompanying this climate change is the worry of losing the ecosystems we have around the planet."

"X, and with it Y" means that first X will happen, and then Y will happen as an inevitable consequence or result of X. "Bob lost his job, and with it, his wife's respect." First, Bob lost his job. Then, because he didn't have a job, he lost his wife's respect. "Jill won the prize, and with it, got revenge on everyone who said she would fail."=Jill won the prize, and because she won the prize, she was able to make all the people who doubted her feel bad. So we are afraid that climate change will come, and we are afraid that when it comes, it will destroy the planet's ecosystems.

Yes, the "it" means climate change. The "with" can be substituted in this case with "in addition." So the sentence can be interpreted as, "Climate change is always a worry, and, in addition to it, is the worry of losing the ecosystems we have around the planet."