By elimination, only (B) is true. (A) is false - while water vapour has high radiative forcing, it is not "an important greenhouse gas" in the big picture, unl

By elimination, only (B) is true. (A) is false - while water vapour has high radiative forcing, it is not "an important greenhouse gas" in the big picture, unlike what the coal industry reps say. This [1] should explain why. Methane and CFCs are far less important in aggregate (about 1/3 and 1/4 of the effect of CO2 respectively), although they are far more dangerous per unit of volume. (C) is obviously false - even in the low level layman explanation in [1] you can see that they include a table with the forcings of various combinations (like H2O vapour+CO2); you can also see that the table is from 1978, so scientists have done that since way before you were born. (D) false [1] http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/ http://www.realclimate.org/index.php/archives/2005/04/water-...