What is the maximum CO2 level prior to Year 0? (give answer in parts-per-million, or ppm) What is the minimum CO2 level prior to Year 0? What was the natural range (difference between maximum and minimum values) in CO2 prior to Year 0? #8 What is the minimum number of years it takes for the natural system to change from a high CO2 concentration to a low CO2 concentration? (i.e., what is the fastest time in which this change has occurred naturally?) -- Use only the pre-Year 0 values. #9 The CO2 concentration recorded in 2006 was 382 ppm. How much higher is this than the maximum value prior to Year 0?