How about the very mechanism of warming shows AGW theory to be a failure. UV radiation penetrates 500 meters deep into the ocen to warm it. The oceans govern the heat of the planet. Long wave IR (the claimed engine of warming) is not capable of penetrating the skin of the water, thus the theory fails its very first test.
Mamooth got it right above. Here is my similar explanation.
The theory does not fail. Yes, the short wave radiation from the sun warms the ocean and the long wave IR cannot penetrate it. (The long wave IR can't penetrate much of anything else on the earth.)
But remember that, night and day, the surface of the ocean and earth is loosing around 400 Watts per square meter of thermal IR radiation (Stefan-Boltzmann law). That radiation is leaving from within the top few microns of the surface.
The greenhouse gasses, (including water vapor for the most part), are continually backscattering a large percentage of that loss as IR right back to that same thin top surface. Otherwise the surface of the ocean would quickly freeze everywhere.
The net result is that the thin surface is not loosing as much heat through IR as it would otherwise. That is why the ocean can retain the short wave radiation heat that the sun provides.
Try to remember that scientists do not (or should not) claim that IR backscatter actually warms anything. What backscatter does is to prevent a lot of heat from escaping from the already warm earth. (Warmed by short wave radiation.)