This video, filmed Dr. Jason Kruse on the University of Florida campus, shows the differences in temperature between natural and synthetic turf, as well as a comparison of both to concrete and asphalt. You may be surprised at the results.
From the YouTube description:
Surface Temperatures of Natural and Synthetic (Artificial) Turfgrass Systems in Gainesville, FL
This video was shot on the UF campus on 7/13/10 to demonstrate the difference in surface temperature between a synthetic and natural turf system. In addition, there are photos showing the temperatures of asphalt and concrete on the same day. Ambient air temperature was around 94 degrees