It is relatively little, but it's actually something like 6%. The rate of change of the Earth's heat content is something like 250TW (on average); humans are c

It is relatively little, but it's actually something like 6%. The rate of change of the Earth's heat content is something like 250TW (on average); humans are currently using/generating around 16TW of energy. For comparison, the Earth's fiery core is about 45TW of radioactive decay and sunlight hitting Earth is about 173PW. Of course, we've historically increased our energy use by around 5% per year, so if that trend held (which you should expect about as much as any other exponential trend holding...), in about 50 years waste heat would begin outweighing greenhouse gasses.