This short video is a simple explanation of how humans have caused carbon emissions over the last 260 years.

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Unless we begin sharp reductions in carbon emissions immediately, we will commit the world to more than 2 degrees C of warming.

[youtube https://www.youtube.com/watch?feature=player_embedded&v=urewQRnA9iM]

It can be a little dangerous to think that we still have carbon to spend.  In terms of ocean acidification and feedback risks, we have already emitted too much.