Problem Set #4
Modeling the Earth's Climate Using One-Layer Energy Balance Model
For this activity, you will explore the warming of the surface and the atmosphere due to increases in CO2 using a one-layer EBM climate model. You will consider/investigate the role of various feedbacks in the climate system (water vapor, ice, and clouds), the influence they have on climate sensitivity, and the impact of the uncertainties in the precise magnitudes of the feedbacks.
- First, save the Problem Set #4 Worksheet to your computer. You will use this word processing document to electronically record your work in the remaining steps.
- Save the worksheet to your computer by right-clicking on the link above and selecting "Save link as..."
- The worksheet is in Microsoft Word format. You can use either Word or Google Docs (free) to work on this assignment. You will submit your worksheet at the end of the activity, so it must be in Word (.doc) or PDF (.pdf) format so I can open it.
- You may find it useful to cut-and-paste graphics and output from the screen (e.g., by first printing the output to a pdf file) and then directly inserting into the worksheet, along with text providing discussion and conclusions.
- Using the on-line one layer EBM application, double the CO2 concentrations relative to the pre-industrial level and calculate climate sensitivity and also warming of the mid-troposphere for the following three cases: (A) no feedbacks (i.e., cloud feedback, water vapor feedback, and ice feedback factors all set to zero); (B) mid-range feedback factors (i.e., the default settings); (C) high-end estimates of the feedback factors (i.e., the highest settings allowed by the sliders). How does your calculated climate sensitivity range compare with the prevailing range of climate sensitivity estimates? In each case, does the mid-troposphere warm more, the same, or less than the surface? Is this pattern of warming consistent with the predictions by the state-of-the-art climate models? If not, what physics do you think might be missing in our one-layer model?
- For the doubling of CO2 for the same three cases (A), (B), and (C) explored in Question 2, please answer the following questions. What are the long wave and short wave forcing, and the total surface forcing (i.e., the sum of the two)? Calculate the overall feedback factor. To do that, first take the ratio of the total surface forcing to the forcing due to the direct radiative impact of CO2 doubling alone, which simply equals the total forcing in the “no-feedback” case (A); then subtract one from this ratio. What are the Earth’s albedo and the atmospheric emissivity? For cases (B) and (C) is there a change in the Earth’s albedo and atmospheric emissivity compared to the “no feedback” case (A)? Which feedbacks must be responsible for the observed changes in each case?
- Save your word processing document as either a Microsoft Word or PDF file in the following format:
PS4_AccessAccountID_LastName.doc (or .pdf).
For example, student Elvis Aaron Presley's file would be named "PS4_eap1_presley.doc"—This naming convention is important, as it will help me make sure I match each submission up with the right student!
Submitting your work
- Upload your file to the "Problem Set #4" dropbox in ANGEL by the due date indicated on our ANGEL calendar.
The instructor will use the general grading rubric for problem sets to grade this activity.