Posted 10 October 2011 - 22:52
The difference is in the incoming radiative energy at the earths surface. GHGs likely are responsible for the downwelling of roughly 1.85 watts / m^2 of IR 24 hours/day where solar variation at the same detection point is responsible for roughly 0.54 watts/m^2 every 11 years. The solar variation is full spectrum, having higher energy photons; however, the narrowness of the UV band actually balances out the broader IR band as to total energy potential. Meaning that GHGs offer 325% the energy of solar variations over the last 44 years and 1100% more often.
Even so, the GHG contribution is only 0.5% of the distributed solar input (7x24, 365 days). At best looking at global influences, the addition seems small; however, if you add in several other man made influences, the amount of energy availible to push natural variation far enough to upset the apple cart is present.
Removing GHG emissions will not overcome other man made influences; however, they are potentially the most important. Not the 5 Gt of Carbon from today; but, the potential 20Gt of Carbon by 2050. Though if we look at the historic peaks since 4 limbed life crawled out of the sea, the maximum heating that Carbon could contribute to the average global temperature is roughly 7deg. C and 14deg.C at the poles. (Added temperature, not absolute.) Though you also have to keep in mind there is not enough recoverable Carbon to exceed 1/2 of those values today. Finally, remember that the man made contributions are not the source of global warming, they push the natural systems to patterns that cause warmer surface conditions.
I will stop there as this is likely more then would be appropriate for a chat; but, maybe a good starting point for a couple chating threads where we can examine the differences in understanding many have when we discuss this issue.
As a final note, consider that for definitive values of natural changes, they are the best guess based on what Science is aware of today. Tomorrow may offer different insights, the hope is we can find a way to offer future generations similar environmental experiences as to what we grew up with, (Camping, Fishing, Hiking, Canoeing, Sailing, Skiing, Sleding, Gardening, Stargazing, Storm Chasing....).