The anti-greenhouse effect is a process that occurs when energy from a celestial object's sun is absorbed or scattered by the object's upper atmosphere, preventing that energy from reaching the surface, which results in surface cooling – the opposite of the greenhouse effect. In an ideal case where the upper atmosphere absorbs all sunlight and is nearly transparent to infrared (heat) energy from the surface, the surface temperature would be reduced by 16%, which is a significant amount of cooling.[1]
This effect has been discovered to exist on Saturn's moon Titan.[2][3] In Titan's stratosphere, a haze composed of organic aerosol particles simultaneously absorbs solar radiation and is nearly transparent to infrared energy from Titan's surface. This acts to reduce solar energy reaching the surface and lets infrared energy escape, cooling Titan's surface. Titan has both a greenhouse and an anti-greenhouse effect which compete with one another. The greenhouse effect warms Titan by 21 K while the anti-greenhouse effect cools Titan by 9 K, so the net warming is 12 K (= 21 K - 9 K).[3][4]
It has been suggested that Earth potentially had a similar haze in the Archean eon, causing an anti-greenhouse effect.[5] It is theorized that this haze helped to regulate and stabilize early Earth's climate.[5] Other atmospheric phenomena besides organic hazes act similarly to the anti-greenhouse effect, such as Earth's stratospheric ozone layer[4] and thermosphere,[3][4] particles formed and emitted from volcanoes,[6] nuclear fallout,[3][6] and dust in Mars's upper atmosphere.[6]
Outside of the Solar system, calculations of the impact of these hazes on the thermal structure of exoplanets have been conducted.[7]
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