Fourier realized back in 1824, that solar radiation alone is not enough to warm earth to its temperature levels. The effective temperature of earth is around -20°C. Absorption and emission characteristics of CO2 and other greenhouse gases are also well understood, as is the makeup of the atmosphere.
The IPCC's carbon budget for having a 66% chance of staying below 2°C degrees of warming is 1000 billion tons of CO2 starting at 2011. We've already blown 20% of this budget by 2016. We currently emit around 40 billion tons of CO2 per year.
IF developing nations peaked their CO2 emissions in 2025 and then would ramp up mitigation to 10% of emission reduction per annum in 2035, the west would STILL need to start cutting emissions by 10% a year RIGHT NOW and be fully decarbonised in 2035.
You can't engineer your way out of this. The logical, painful and horrible conclusion is that we need to have massive reductions in consumption.
For instance, nuclear, it currently provides around 2% of total energy consumption of the world with 450 reactors. Imagine the amount of reactors we would need to build just to make a dent here... You can't build reactors fast enough. The same with wind, renewables and so on.