Homework 3 - Greenhouse Gases Homework 3 - Greenhouse Gases EART 12 Intro to Weather and Climate Fall 2019 Use the online model at http://climatemodels.uchicago.edu/modtran/ to answer the following...

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Homework 3 - Greenhouse Gases Homework 3 - Greenhouse Gases EART 12 Intro to Weather and Climate Fall 2019 Use the online model at http://climatemodels.uchicago.edu/modtran/ to answer the following questions. For each part, make sure you are starting from the default model configuration (1.7 ppm methane, 400 ppm CO2 concentration, etc.) You will submit your work by uploading a file to Canvas. The doc should include for each question a short answer in words along with numeric values you obtained from your model experiments to support your conclusion. Methane 1. Would an additional 10 ppm of methane in the atmosphere have a larger or smaller impact on the outgoing IR energy flux than an additional 10 ppm of CO2? 2. Where in the spectrum does methane absorb? What concentration does it take to begin to saturate the absorption in this band? 3. Would a doubling of methane have a larger or smaller impact on the IR energy flux than a doubling of CO2? 4. How many ppm of CO2 would lead to the same change in outgo- ing IR energy flux as doubling methane? This is called the "equiv- alent CO2" of doubling atmospheric methane. What is the ratio of ppm CO2 change to ppm methane change? Water Vapor 1. How much does the outgoing IR energy flux increase for a 5◦C increase in surface temperature? What effect does the surface warming have on the shape of the IR spectrum and why? 2. Up to this point, you have held the amount of water vapor fixed (the default model configuration, i.e., constant water vapor pres- sure). However, more water can evaporate into warm air than cool air. Set the model to instead hold water vapor at fixed relative hu- midity, which will allow the amount of water vapor to increase with warming. Calculate again the change in outgoing IR energy flux that accompanies a 5◦C temperature increase. Is it higher or http://climatemodels.uchicago.edu/modtran/ homework 3 - greenhouse gases 2 lower? Does water vapor make the Earth more or less sensitive to climate change? 3. Let’s investigate this effect in another way. Record the outgoing IR energy flux. Now, increase CO2 concentration to 550 ppm. The temperature in the model stays the same (it’s how the model was coded), so the IR energy flux decreases. Holding water vapor pressure fixed, increase the temperature offset until you get the original IR energy flux. What change in temperature is required? Now repeat the calculation holding relative humidity fixed. What change in temperature is required? Does water vapor make the Earth more or less sensitive to CO2 increase? Methane Water Vapor