Time and time again have I heard people talk about small Earth and save planet. I hope that this little post can put things back in perspective. Note that none of this is meant to be an excuse for the things we do wrong, I just wanted to post my viewpoint, nothing more.
The planet is far too large for us to save it from anything with our current scientific knowledge and technology. Fact is, that this planet is absolutely enormous: Suppose the Earths radius was just one meter. I'm 1.93 meters, so it would stick out seven centimeters above my head. Now picture a 6.5 kilometer high mountain (to humans thats huge). On the scaled down Earth, it would only stick out one millimeter. Deepest point in the ocean? Nothing more then a two millimeter dent. It's clear from these figures that this planet isn't going anywhere soon.
In the past the Earth has been hit by a rather large rock from space, and the energy released by that impact was far greater then anything we could come up with today. That impact had an enormous effect on life on Earth, yet it left only a tiny little dimple in the earths surface (compared to the Earths size). With our current knowledge, it won't be easy to stop such an event if it would ever happen again, and compared to what it takes to destroy Earth, that rock was probably a little grain of sand. If such a planet destroying monstrosity would ever be heading our way, then we'd be completely powerless to stop it. Hopefully we can do better in the future.
The environment is a different story. Because of the sheer size and intensity of our operations today, we are making changes to a very changeable system. To the Earth, those changes are unimportant. To life, those changes can be huge and dangerous. Such changes have occurred in the past naturally and were responsible for the extinction of many species. While our own influence isn't having those vast effects yet, we have made a mess out of things. It's a fact that the environment is a very changeable and flexible system, and that life can have a very hard time to adjust to those changes, and is often powerless to directly stop those changes.
Furthermore, life on Earth is ridiculously minuscule compared to Earth, and other common objects in space. The radius of our sun is already more then a hundred times larger then Earths radius, and our sun is only a small star compared to the big ones! Life on Earth has always been living on the edge, and nothing we can do today, can stop that. Also, just consider the fact that the most numerous lifeforms can't even be seen with the naked eye, yet they can potentially evolve to become dangerous enough to wipe us out, just like that, and our medical knowledge would be powerless to stop it. While we are certainly a threat, we are not alone, and not even the biggest. There are potential threats from Earth, besides us, and there are threats from space.
The big difference with us and other threats is, that at least we can stop ourselves from being a threat. Evolving microbes certainly can't, and a large asteroid can't either. We are also able to reverse at least some of the damage we have caused to life, and undo some of the changes to the environment by taking any responsibility we can.
With us, life has reached a new level, and we should do our best to make sure we aren't just an evolutionary mistake, like viruses are (probably). Remember, what we are is new to life, and it may take some more evolving for nature to get it right, if so, let us at least try to make that possible, by minimizing the damage we cause, and to clean up after ourselves when ever we can.
I hope that at least someone found this a little interesting.