The conventional greenhouse effect occurs because the atmosphere is largely transparent to solar radiation, but largely opaque to infrared. In an anti-greenhouse effect, this situation is reversed (i.e. the atmosphere is opaque to solar, but lets out infrared).
The haze containing organic molecules in Titan's upper atmosphere absorb 90% of the solar radiation reaching Titan, but is inefficient at trapping infrared radiation generated by the surface. Although a large greenhouse effect does keep Titan at a much higher temperature than the thermal equilibrium, Titan also exhibits an "anti-greenhouse" effect, which partially compensates for the greenhouse warming, and keeps the surface approximately 9°C (16°F) cooler than would otherwise be expected from the greenhouse effect alone. According to McKay et al., "The anti-greenhouse effect on Titan reduces the surface temperature by 9 K whereas the greenhouse effect increases it by 21 K. The net effect is that the surface temperature (94 K) is 12 K warmer than the effective temperature 82 K. [i.e., the equilibrium that would be reached in the absence of any atmosphere]"
In addition, this effect results in a permanently inverted thermocline on Titan with atmospheric temperatures increasing with increasing altitude above the tropopause. This type of anti-greenhouse effect is only known to occur on Titan, however it is similar to the cooling effects suggested for nuclear winter.
A different mechanism exists on Pluto, which is not a true anti-greenhouse effect. Sunlight striking the nitrogen ice on the surface of dwarf planet Pluto causes it to sublimate; this causes the temperature of Pluto to be about 10°C (20°F) lower than its moon Charon. The sublimation causes cooling, and is analogous to solar radiation evaporating water on Earth; however when this occurs on Earth it is not called an anti-greenhouse effect. This effect was discovered using the Submillimeter Array in Hawaii.