So our total impact on the planet is a matter of both population numbers and the average environmental impact each of us makes. It depends entirely on consumption. But with a typical North American way of life the figure has been shown to be closer to 2.5 billion - and there are already 6 billion of us on Earth. Unfortunately, it isn't possible to draw that conclusion. There are some good historical examples of what happens when population growth and consumption outstrip the available resources.
Easter Island is one that springs to mind.
When the island was first visited by Westerners in the seventeenth century, there was evidence that it had once supported a far higher population and a higher level of civilization than was then in evidence. In fact, it was thought that the island had once been inhabited by a race of supermen. Research has revealed that a once-flourishing society on a green and pleasant island outgrew its resources. Almost all projections for future world population growth show it stabilizing at some point in the future. While this may happen, it is not the most likely scenario.