Actually if you look at man's activity over the last couple of hundred years since we have been using coal, oil, etc. you will see that man has influenced this planet more and in more ways than has ever been seen or recorded since man has been observing history. We live in an unprecedented time and have no real reference to compare our effects on the planet today as, say, during the first 1000 or 1500 years after Christ. In the last 10 years we have used more energy than we did in that entire period I'd say. What did they have as energy then? Whale oil, maybe kerosene lamps and wood?
One person can do about 100 watt/hours of work. (try it, sit on a bike with a generator and see how much energy it takes to make 100 watts for an hour, I'll bet most people couldn't do it) but let's say that one person can put out 100 watt hours for 8 hours which is an exorbitant amount of energy, by the way. So that = 800 Wh. A gallon of gas is about 10 KWh if I remember so 10e3/800 = 12-1/2 days of one man working (it's probably more like 20 days but we'll be conservative here)
So think about this, your wife goes to the store for a gallon of milk, picks up the kids from school and runs a few other errands. Maybe she uses 2 or 3 gallons of gas at 20 to 25 mpgs running around. So now we're talking about one person working a couple of months and we're not including the energy the farmer used to plow his fields to make that milk or the energy to pasteurize it and bring it to market. The energy to light the market, freezers, the energy to maintain the roads, stop lights, materials to make the carton, etc.
At the end of the day most families use more energy than a family 300 or 400 years ago used in a couple of decades if not a life time. That's how much energy we use without realizing it.
What's that effect on the environment? Monumental, so we can't say that 10 or 20 years is too small a period of time because time is not linear, its been distorted by our tremendous energy demands and usage, unprecedented in history, even 100 years ago.
Now, who here thinks we can keep doing this indefinitely?
Rob