I believe it is both. The CO2 helps to trap more of what the earth receives from the sun (primarily what is talked about with global warming), but our energy use is also staggering. I can't recall off the top of my head but we currently consume something equivalent to ~0.1% of the total solar radiation incident on the earth (through all means - oil, gas, solar etc). At that scale, the energy use alone is on the scale of other warming effects, wild!