Well, obviously, because the concentration of most greenhouse gases are rising, the balance between sources and sinks is off. I believe that the amount emitted by sources is higher than the amount absorbed by the sinks. In my personal opinion, I believe that a really high population is contributing to this unbalance. We exhale large amounts of CO2 and there are over 5 billion of us on this Earth. Also, the increase of people driving cars adds to the amount of CO2 added to the atmosphere.
