A question I get asked alot is "Is humanity the cause of climate change". The short answer is yes, no, or maybe. It all depends upon your point of view. From my point of view, species homo sapiens is as much a part of this world as any other species. Therefore, everything humanity does is "natural", and the impacts and effects are natural. When a beaver creates a dam and floods a small valley, is not his work "natural"? And, isn't the flooded vale just as natural as it was before the beaver built his dam? If you look at the quantity of CO2 being released by our machines, it is much less than the CO2 released by world's biosphere each year. However, before the industrial revololution, the biosphere was in balance. For hundreds of thousands of years, atmospheric CO2 varied from 250ppm to about 300ppm. Now we are at 390 ppm and counting. So, it seems that what we have done since the industrial revolution is to upset that balance. Maybe humanity's industrial output of CO2 is small compared to what normally put out naturally, but it is enough to put us out of balance. Thus, the CO2 concentration builds. Another way of looking at it is to take the situation of the overweight man. Lets say he expends 3,000 calories a day. When he was thin he was consuming 3,000 calories a day, and kept his trim shape. However, he starts eating an additional doughnut a day, and increases his calorie intake to 3,300 per day. What is the result? Obesity. Now, is the doughnut the cause? Not really. If he had cut out something else, and kept his intake at 3,000 calories, he would have been OK. So, do we blame the doughnut or his overall diet? Now the earth's CO2 production is from the biota and humanity. I see humanity's CO2 production as being like that man's doughnut. It may be the minority, but it is what puts the earth's carbon cycle out of balance. Thus, slowly, inexorably, our CO2 levels build. So, is humanity the cause. In the sense that we have created the imbalance, then yes. However, the climate change deniers will point out that humanity's CO2 contribution is small compared to what the rest of nature puts out each year, so they say we are NOT responsible. I say, it depends upon your point of view.