In answer to the does it matter question, the answer is (from me at least) a resounding yes, of course it matters that we look after the planet. Apart from the Love of Life arguement that was made so well by Chris yesterday, there is the fact that there are many other species whose survival is dependant up upon our actions.
In modern times animal extinctions have increased rapidly. Whilst it can be difficult to pinpoint the exact cause of a species extinction (indeed there maybe several combining causes) the most common given causes include hunting, habitat destruction an the human introduction of competitive species.
So far only one mammal has been declared extinct as a direct result of global warming, the Lemuriod Ringtail Possum. Even that may not have vanished completely yet, as there are three recorded sightings post-dating the time that it was declared extinct. However, with the IUCN Red List
listing over 1100 species as in danger of extinction the Lemuriod Ringtail Possum is unlikely to be the last.