We passed a milestone of sorts today:
Many of the problems the world has today (hunger, climate change, peak oil) are a direct result of the increasing population of this planet. Over six and a half billion humans certainly can make a difference to the planet's health, and it's going to get worse before it gets better. The Wikipedia article on World population has many interesting facts and figures about how the population of the Earth is changing.
The good news is that the rate of growth peaked in the 1950s at about 2.2% annually, and has been steadily dropping since that time. It is now estimated to be about 1.2%. Nevertheless, we will probably reach 9 billion by about 2050.