What is the speaker's take on waiting for proof on environmental issues and their stance on the consensus amongst scientists about humans impacting the Earth?
Yeah, you're probably right.  Let's just wait another 50 years until we know unequivocally, 100% damned sure that we've screwed ourselves.  Then let's start to come up with a plan on what to do.  That'll probably work out well for us...
I've got news for you - the physics of flight isn't fully understood yet (nor is anything else related to fluids).  But somehow we've managed to do pretty well with what we DO know about it, don't you think?  Maybe there's a lesson there.  
Not every scientist "believes" in evolution.  Yet it has been going on for more than a billion years despite what some believe.  
As soon as you have evidence that convinces more than half the world's scientists to believe that humans are NOT screwing the earth over, I'll believe it.  Until then I'm going with the 97%.