Define environment. It's naive if you understand the size and scope of the earth and how small of a footprint humans have on it to think we can change the environment globally. There just ain't enough of us on the planet to have the same effect as termites or simple bacteria both of which outweigh us by hundreds or thousands to one, and they both produce 'greenhouse gasses.'
Yes, humans can foul a local area -- a very local area. But the entire planet??? Not a chance. There just ain't enough of us to do the job.
But bugs can do it which is the only reason we have a breathable atmosphere to begin with. Those little polluting suckers plus those tenacious green things we call grass and weeds and trees create the very air we breathe.
There is no doubt they other far more populous life forms have an effect on the environment, but if humans had to create the same atmosphere, we would be unable to do it. Their ain't enough of us to get the job done.
It was only about 350 - 400 million years ago that cyanobacteria evolved to the point they began creating oxygen, and fixing iron and CO2 into compounds that were deposited in the oceans.
In doing so, they created the oxygen rich atmosphere we have today.
One of those organisms was called the Stromatolites, an ancient ancestor of today's corals.
Cyanobacteria are still operating the same way today, creating oxygen in the oceans.