Compare current CO2 levels to the concentrations from the past 450,000 years. Based on these websites and the textbook, answer the following questions:

Explain how the carbon cycle works.
What is the current CO2 concentration in parts per million (ppm)?
How does this compare to the highs or lows over the past 450,000 years?
What are the three most abundant sources from which humans add CO2 to the atmosphere?
Explain the two main natural carbon sinks that remove CO2 from the atmosphere.
Explain in detail two ways deforestation contributes to the increase in CO2 levels.
What are some other greenhouse gases, and how do their concentrations compare to the past 450,000 years?
Based on the data, are humans contributing to climate change, or is it strictly a natural part of the cycle? Defend your answer. You must weigh all of the data, and use them to formulate your conclusion.