According to an article in the journal Science by D. Hanel and his collaborators, ( 4 July 1986 page 72), the observations taken by Voyager 2 did show a 2-3 degree difference in temperature between the illuminated south pole and the dark north polar regions as measured by the IRIS instrument, but because the illuminated region was measured 597 times, and the dark region was measured only 100 times, they suggested that the temperature difference may have had more to do with calibration uncertainties and pointing errors. The temperature gradient they inferred from the spectra indicated that at the 90 millibar level, the illuminated region had a temperature of about 52 K while the dark region was 56 K. The uncertainties in these measurements could be as large as a few degrees, so these differences may not be meaningful. However, it is known that at 5 microns, the emission from Uranus is dominated by many absorption bands from Methane, and various hazes. If these Methane- rich hazes went away in the dark regions, there might be slightly less opacity in the dark atmosphere so that perhaps more of the internal heat from Uranus might escape, making the planet appear slightly warmer on its dark side.