While the greenhouse effect is still a significant contributor - and will become more so as GHG levels in the atmosphere rise - simply the heat released when burning fuels is also being stored in the atmosphere, as well as in the earth, sea, and arctic ice.
The researchers have calculated that the heat energy accumulated in the atmosphere corresponds to a mere 6.6% of global warming, while the remaining heat is stored in the ground (31.5%), melting ice (33.4%) and sea water (28.5%). They point out that net heat emissions between the industrial revolution circa 1880 and the modern era at 2000 correspond to almost three quarters of the accumulated heat, i.e., global warming, during that period.
Their conclusion is that simply capturing our CO2 emissions, will not prevent global warming. We have to actually reduce the amount of heat we are releasing into the world via our energy use - which mostly involves burning things, and therefore generating waste heat.
The good news is that solar photovoltaics, wind power, even solar thermal generate much less, or even negative, waste heat than either conventional energy sources, or nuclear energy. And of course energy efficiency is the cheapest and most cost-effective mitigation we have at our fingertips.