Slide 19 of 26
Suppose now the concentration of greenhouse gases is increased, while the incoming solar radiation and the clouds remain the same. After the system has come into radiative balance:
(1) the ERL is higher in the atmosphere, because the same total amount of greenhouse gas must be above it.
(2) the outgoing radiation must still be 342 - 105 = 337 W m-2 . Thus the temperature at the ERL must be the same as before
(3) since the temperature decreases with height, yet the ERL has gone up, the only way (2) can be true is for the whole temperature profile to be warmer than before.
The SOLID sloping and horizontal lines show the NEW positions of the temperature profile and ERL respectively. The DASHED sloping and horizontal lines show the corresponding OLD positions. Because of (3) the sloping temperature profile is to the right of the dashed one, i.e.
(4) the whole atmosphere down to the surface is WARMER than before.
Study Question: Suppose that as it got warmer due to more CO2 the amount of reflecting cloud became less. What would that do to the ERL, and to the temperature