GREEN­HOUSE GAS

BBC Earth (Asia) - - Science -

We’re used to hear­ing about hu­man­gener­ated car­bon diox­ide con­tribut­ing to the green­house ef­fect, but the ma­jor green­house gas in Earth’s at­mos­phere is ac­tu­ally wa­ter. A planet’s tem­per­a­ture is de­ter­mined by the bal­ance be­tween the in­com­ing so­lar en­ergy and the heat that’s ra­di­ated away. If our at­mos­phere didn’t con­tain any wa­ter, the en­ergy flow­ing in and out would be bal­anced at an av­er­age tem­per­a­ture of -18°C. Wa­ter vapour in the at­mos­phere di­verts some of the out­go­ing heat (via the green­house ef­fect), and shifts the bal­ance point to a far more pleas­ant 14°C. Hu­man-gen­er­ated green­house gases are now nudg­ing the av­er­age tem­per­a­ture even higher.

Wa­ter helps our planet stay at a balmy av­er­age of 14°C

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