Question 1
In this quiz, we will use the RRTM Earth's Energy Model. Instructions for using this model are available on the doc page by clicking on "how to".
Go to the Earth's Energy model. This model estimates the balance of energy flowing in and out of the Earth given certain conditions of the Sun, surface, and atmosphere. The values for the surface and atmosphere are assumed to be uniform across the whole Earth, and the fluxes (the arrows) are calculated as averages.
First, set up the model with an isothermal atmosphere by setting the Lapse Rate (temperature change with altitude) to 0. Check the total outgoing longwave radiation (OLR) by hovering on the blue up arrow. It should be ~372 W/m2. Now, let's see how things change when we change the CO2 concentration in the atmosphere. Double the CO2 concentration to 800 ppm. Hover over the blue arrow to see the new value for outgoing longwave radiation.
How much has the OLR changed? Type in the difference in W/m2 between the old and new value below. Think about why this might be the case.
1 point
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2.
Question 2
Now, without changing the value of CO2, let's give our atmosphere a nonuniform temperature profile. We'll do so by turning up the lapse rate from 0 K/km to 10 K/km, about the value you would get from dry convection. This gives our model atmosphere a troposphere with declining temperatures up to a stratosphere at 15 km. Now look at the outgoing longwave radiation (the value when you hover on the blue up arrowhead). About how much less, in W/m2 is the OLR at the top of the atmosphere than it was before? Think about why this answer might be different than above, and notice what happens to IR radiation from the atmosphere as it passes through Earth's atmosphere.
1 point
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3.
Question 3
Now adjust the Earth's Surface Temperature to bring the Earth back into energy balance. Note that when you change the surface temperature, you're also changing the temperature of the atmosphere, which is determined according to the surface temperature and the lapse rate. By about how many degrees K do you have to increase the surface temperature to balance the Earth's energy budget?
1 point
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4.
Question 4
When an atmosphere is saturated with water, it follows the moist adiabat instead. Set the CO2 concentration back to 400 ppm. Set the lapse rate to 5 K/km, which is typical for a moist adiabat, and adjust the temperature to regain balance. Double the CO2 concentration, and find the new temperature at which the energy fluxes balance. By how many degrees K do you have to change surface temperature (relative to before you doubled CO2 in this question) to regain equilibrium? If you had to increase the temperature, put a positive number; otherwise, put a negative number.
1 point
Enter answer here
5.
Question 5
When a column of air gets warmer, its H2O concentration typically increases. This has two effects: it adds water, a greenhouse gas, to the column, which behaves much like CO2 did in question 2. This is known as the water vapor feedback. It also makes the lapse rate smaller, as occurred in question 4. This is known as the lapse rate feedback. A positive feedback is a consequence of global warming that leads to further warming, and a negative feedback is a consequence of global warming that lessens the amount of warming.
Given this, which describes the two feedbacks?
1 point
The water vapor feedback is a positive feedback and the lapse rate feedback is a negative feedback.
Both the water vapor and lapse rate feedbacks are positive feedbacks.
The lapse rate feedback is positive and the water vapor feedback is negative.
Both the water vapor and lapse rate feedbacks are negative feedbacks.
