From my friend DWN.

Here is a list of natural causes that affect global atmospheric temperatures:

• solar activity (frequency and strength of sun flares)
• geothermal vents and underwater volcanoes cosmic ray flux
• orbital eccentricity-axial tilt-and-precession of Earth’s orbit
• magnetic effects of other planets
• heat distribution between oceanic and atmospheric systems
• changes in radioative forcing (balance between solar-radiation energy absorbed by Earth’s  surfaces and energy radiated back into space)
• the large difference in land:sea ratio between the Northern and Southern Hemisphere

“Human activity” contributes something, but the effect is well under 1%, i.e. it’s not statistically detectable. (Yet. Could be in 100-500 years.)

Really nice video from NASA here.