On average, 2 W/m2 are absorbed from the sun which contributes to heating of the atmosphere. The surface type, itself, effects that. The darker the surface, in general, the more is absorbed as opposed to reflected. Cadmium telluride to produce PV is very dark; the mirrors used on thermal solar are extremely reflective. Of course there's a lot of surface area on the planet but every little bit matters.
When a material absorbs the energy outright, the warming is done instantly making greenhouse gases moot. If the surface reflects it, the density, type, and altitude of the greenhouse gases determine, on average, how much is reflected back at Earth and this cycle repeats until the energy either leaves the Earth or it is completely absorbed in the atmosphere or on the Earth.
Imagine if the entire planet had a mirror finish. Earth wouldn't be very warm because even with an unchanged amount of green house gases, most of that energy will escape because the Earth absorbs very little of it.
http://www.firstsolar.com/en/solutions/fuel-displacement
PV by itself may have a tiny bit lower CO2 emissions than nuclear but when you add the natural gas in required to supplement solar, PV isn't even close. Even if people are putting these panels on their own houses and connected to the grid for night power, those natural gas plants have to be built to fill in the gaps. I already demonstrated this happened in a big way at PSE&G.
I can't find the page your picture is on. I'm really curious what that asterisk is for.