“…what do you think is driving the increasing energy in the system as shown in your graph?”
My take is: the most of the increase is driven by the increase in solar cycle frequency (decrease in solar cycle length). This explanation will be put to the test in the next decade. There was a very significant increase in solar cycle length from sc22/23 to sc24, which predicts a significant temperature decrease.
http://arxiv.org/pdf/1202.1954v1.pdf