As said above...it is impossible for humans to be here WITHOUT making an impact on the environment. I also believe that the earth will be just fine with or without us and regardless of what we do...the question is - will WE still be here regardless of what we do?
In the grand scheme of things, humans require VERY specific climactic conditions. Luckily we have adapted with warm clothes, heating sources, etc so that we can survive in almost any condition. I'm sure that if the climate does undergo a drastic change, we will adapt to that as well.
I used to be a HUGE global warming sceptic, but then I started putting some serious thought into it. It is obviously true that we are impacting the environment...it is also true that there are A LOT better ways to do the things that we're doing.
So why not? Sky is falling or not, what is the real case for INACTION? cost is a big prohibitor, obviously. I've undergone multi million dollar energy savings projects for the government and they are not cheap...but here's the crazy thing....they pay themselves off. Just changing all of the light switches to motion sensors paid itself off within 6 months on one military establishment - it now saving the base and the government over $60,000 per year. So I say again....why not? We are saving money, lessening our energy demand, thereby lessening the use of fossil fuels, etc etc etc. So why not?
Now converting an entire existing building to a "green" establishment is HUGELY cost prohibitive....even building one is cost prohibitive. But look at the little things. Solar power for example, build it into a building, it increases the up front cost a bit, but in construction, up front is the time to put the money in....but over the long term, it will save a massive amount of money.
So I ask again.....why not?
It seems to me that whether there is or isn't a problem, it isn't a difficult fix and there's no reason not to. If everyone does a part, the problem goes away.
On another note, there is a lot of sceptisim about the issue...and most of it seems like excuses to me. "Well, there's no problem, so let's not change anything." Whether it is a global climactic problem or as simple as smog over cities - I think that everyone can agree that we have some problems in how we treat the environment.