2 00:00:10,467 --> 00:00:17,371 The bottom line is that the temperature structure of the atmosphere is determined by 4 00:00:17,371 --> 00:00:19,683 series of processes that we talked about in various lessons 5 00:00:19,683 --> 00:00:23,720 that all come together and fit together into this picture. 6 00:00:23,720 --> 00:00:30,350 The temperature profile from radiation-only is much steeper than observed 7 00:00:30,350 --> 00:00:35,150 although this is what we assumed implicitly in the layer model to start with. 8 00:00:35,150 --> 00:00:35,490 And then if 9 00:00:35,490 --> 00:00:38,796 we add convection it's not as strong 10 00:00:38,796 --> 00:00:42,630 a temperature difference between high and low, and 11 00:00:42,630 --> 00:00:45,740 then adding water vapor pretty much brings 12 00:00:45,740 --> 00:00:50,100 our ideas into sync with reality. 13 00:00:50,100 --> 00:00:54,190 This is what is really governing the temperature of the atmosphere. 14 00:00:54,190 --> 00:01:01,240 The sunlight puts in energy at the ground, which drives convection, 15 00:01:01,240 --> 00:01:04,160 which is the buoyant fluid rising from below. 16 00:01:04,160 --> 00:01:09,560 The gas expands because it's a compressible medium, 17 00:01:09,560 --> 00:01:14,730 and therefore it cools, which tends to make it cool down as it rises up. 18 00:01:14,730 --> 00:01:17,900 But cooling makes water vapor condense, 19 00:01:17,900 --> 00:01:21,360 because water doesn't like to be vapor if it's really cold. 20 00:01:21,360 --> 00:01:24,860 It would prefer to be in a condensed state like fluid, like liquid. 21 00:01:24,860 --> 00:01:26,390 So the water condenses, 22 00:01:26,390 --> 00:01:29,940 but when the rain falls out, it leaves behind the 23 00:01:29,940 --> 00:01:33,220 heat that was with the water vapor to start with. 24 00:01:33,220 --> 00:01:36,500 The process overall, that looks like 25 00:01:36,500 --> 00:01:40,290 the real thing, is what's called moist convection. 26 00:01:40,290 --> 00:01:44,100 This is what sets the intensity of the greenhouse effect on Earth. 27 00:01:44,100 --> 00:01:47,572 And if there were anything that could change this, like a change in 28 00:01:47,572 --> 00:01:49,184 the amount of water vapor in the 29 00:01:49,184 --> 00:01:51,540 atmosphere or something like that, it could 30 00:01:51,540 --> 00:01:54,073 feed back and change the climate of the Earth. 31 00:01:54,073 --> 00:01:55,864 So it's something we have to think about.