It shouldn't be significant because GW is all about how bad Earth is in dissipating energy into space (in comparison to black body), rather than how much energy flows through. Nevertheless, let's count: according to Wiki, 2012 World energy consumption is 5.6*10^20J; this means we were producing at an average rate of this/seconds in year/area of Earth, which is 0.034W/m^2. Solar input (and thermal radiation output, since Earth is roughly in an equilibrium) is 340W/m^2, making our input 0.1%, about the same as variations due to solar cycles.