Originally Posted by antarius
You know, if the world warms up (which it does naturally anyway), that will create some loss of habitat, without a doubt.
It will also create more rains, which may cause some problems in some area's, but will also make now un-inhabitable area's (like big deserts) habitable and full of life again.
There's two sides to every coin.
Now, to answer your question:
Not in our lifetime.
Actually, last summer, there was a heat wave that swept across Europe, killing thousands of people. Recent research has shown that it it was statistically significantly tied to human impacts on the environment.
We are already seeing the effects of global environmental change. Mostly this is reflected in more variable and extreme weather, the expansion of deserts, change in rain patterns, loss of delicate and temperature sensitive habitats like coral reefs, and other such negative effects... Unfortunately, since it doesn't look like Day After Tomorrow, many people are pushing it to the side claiming it's minor, or may not even exist at all. The fact is that the worldwide environment is changing faster than it has ever naturally done before (with the exception of cataclyismic disasters striking the planet) should be more than enough of a signal that something's wrong...
Dunno, when 1500 of the world's most influential scientists sign this document, something must be awry:
http://dieoff.org/page8.htm
(I know the formatting on that page is horrilbe, but it's just a transcription of an actual document)