I'm reading Carl Sagan's "A Pale Blue Dot" at the moment. Here's little excerpt from a chapter titled "Is there Intelligent Life On Earth?"
"From your orbital perspective, you can see that something has unmistakably gone wrong. the dominant organisms, whoever they are - who have gone to so much trouble to rework the surface - are simultaneously destroying their ozone layer and their forests, eroding their topsoil, and performing massive, uncontrolled experiments on their planet's climate. Haven't they noticed what's happening? Are they oblivious to their fate? Ar they unable to work together on behalf of the environment that sustains them all?
Perhaps, you think, it's time to reassess the conjecture that there's intelligent life on Earth."