Problem 1 (Scenario and Instructions )

Feedbacks on Earth

There are 4 main forcing agents for climate on Earth. Perhaps 5 if you include large impacts which are rare now, but were more common early in Earth’s history. There are many feedbacks that control the actual response of Earth’s climate to changes in forcings. Many of the responses are nonlinear, which is what makes modelling climate so challenging.The feedbacks pdf goes through a few very simplified responses to change (see course readings ‘The Earth System and Climate Forcings and Feedbacks’). I’d like you to work through one of those examples here. A ‘thought experiment’.Mantle convection and the resulting plate tectonics is relatively constant, but there are variations and there are changes in the convection patterns that develop and evolve over time.

Scenario  (completely fictional, but quite reasonable):

Imagine a plate that includes both oceanic and continental lithosphere is moving along, being dragged by the leading portion of oceanic lithosphere which is being subducted beneath some other continental lithosphere. Finally, all of the oceanic lithosphere is subducted so that a continent-continent collision begins! (Very similar to what would have happened leading up to the India-Eurasian continent-continent collision.)

Before the collision, there would have been a long-lived continental volcanic arc. Once subduction stopped and the collision began, that volcanic arc would terminate once subduction and water release from the subducting plate stopped.On the other side of the incoming continental lithosphere there is still spreading at the ridgecrest, but that spreading has slowed down. The plate is still moving, crumpling up a big mountain belt – but moving slower and slower…So, in that region of the world, there is now no more subduction volcanism, less volcanism/upwelling of magma at the ridgecrest, and a big collision zone has begun to form high mountains.

There are all kinds of different effects this can have on global climate. This is only one region – and for simplicity we will assume that all other processes in all other regions remain constant (probably not true in reality!), but the goal is to think through what effects will be generated by the changes in this region.

Goal

Your goal with this problem is to figure out how climate would respond overall (cooling, warming or no change) to these tectonic/magmatic changes. To do this, consider the various feedbacks discussed here and how they would be influenced by these tectonic/magmatic changes when you work through the following questions. Why or how would a specific feedback respond? What would it affect and how would that affect climate? Over what sort of time interval would each specific feedback occur? (Please note that only a few feedbacks are included here. In reality there would be many more…)

(Questions)

1.     A(n)in episodic CO2 and water output to the atmosphere wouldgreenhouse gas content. This would lead tothat would result in adecrease in volcanism over.

2.     A(n)in episodic SO2 and ash emissions from eruptions would lead to . Volcanic eruptions of ash and SO2 tend to have effects on the atmosphere which last.

3.     A collision which begins thrusting up a large mountain range woulderosion. This is because the erosion of certain types of rocks, when combined with water,CO2 in the atmosphere. This would lead toover.

4.     Correctly complete the following sentence. The principal forcing mechanism(s) producing the feedback loops described in the questions above is (are)…

1)      Orbital variations of the Earth

2)      The Sun

3)      Extraterrestrial impact

4)      Tectonic processes

5)      humans

5.     The principal feedbacks outlined in the first few questions above influence the next set of feedbacks described below due to their overall cooling effects on Earth’s temperature. Hint: You may need to come back to this question once you have worked through the rest of these questions. True or False?

6.     A drop in plant growth meansCO2 used by plants during photosynthesis. This would lead toof Earth over.

7.     Temperatures that arelead to less precipitation. That, combined with fewer plants woulderosion rates. This would lead toof Earth.

8.     The initialwill allow snow/ice to. This willthe albedo of the area, reflectinglight back to space. This leads to an overall. Sea ice would taketo respond whereas glaciers would take.

9.     The main point here is the principal forcing is very slow. The plate tectonic change and the resulting effects of mountain building/erosion take place over millions of years. So, although some of the feedbacks have quite rapid rates of change – all that means is that they nicely track the slow changes due to plate tectonics. True or False?

10. Do you think the final result of a continent-continent tectonic collision like the one described here would lead to a warmer Earth or a cooler Earth? Can you say? (Hint: For part of your answer, think about one of the big assumptions we had to make in order to be able to examine the effects of the individual feedbacks to the area) –  This is a long answer.

Problem 3

(Instructions )

Carbon dioxide is a greenhouse gas. As such, it is partly responsible for the increase in global temperature that we are currently experiencing. Explore the Bathtub simulation shown here to help you answer the questions in the next folder. You may be able to answer some of these directly just using the class readings. However, running tests with the simulations is encouraged to help clarify your understanding.

Bathtub simulation (MIT v.1): Play with the first exercise of the following ‘stock and flow’ simulation:  http://systemdynamics.mit.edu/ghg-exercise/ex-intro-applet.htm

The first page of the simulation uses a simple example of water flowing into and out of a bathtub to provide a nice illustration of ‘stock’ (the water in the bathtub) and ‘flow’ (the inputs and outputs from the bathtub). Do the two exercises suggested (and play with it on your own or play in your own bathtub at home). There is no need to continue onto the next page of that simulation since there is a better simulator coming in Problem 4. [Note: Once you set up the inflow/outflow, you can step through the image of the tub on the left by changing the ‘current time’ number]

1.        Over time, if you pour more water into a bathtub than you drain out, what will happen? (type either ‘empty’, ‘no change’, ‘overflow’ in to the space provided)   In the past, Earth has always reached a balance given enough time, so that ‘inflow’ (carbon sources) = ‘outflow’ (carbon sinks). True or False?

3.        At present, the ‘stock’ of CO2 in Earth’s atmosphere is increasing because the ‘inflow’ (carbon sources) of CO2 are not keeping up with the ‘outflow’ (carbon sinks) for CO2. True or False?

4.      Human activities are the cause of major additional ‘inflow’ of CO2 at present. True or False?

5.        Compare how climate changed on Venus (see Module 4 pdf) with how climate is changing on Earth right now. Don’t go into enormous detail – perhaps 2 paragraphs or equivalent. Consider forcings, additions of greenhouse gasses and sinks (removal mechanisms) of greenhouse gasses. What is the same? What are the differences? I found it useful to play with MIT v.1 simulation to experiment with what happened (continues to happen) on Venus… Just using the bathtub model, you can plug in simple values to help you ‘picture’ what happened(s) on Venus.

Problem 4

(Instructions )

In Problem 4 we move on to applying what you learned in playing with bathtub stock and flow to a simplified climate system. For climate, the central forcings and feedbacks are roughly in balance. Climate is always changing, but it tends to change relatively slowly with significant lag times or delays involved with the effects of increasing or decreasing greenhouse gas concentrations. The amount of human addition of CO2 and other greenhouse gases dwarfs the natural variations and rates. Still, feedbacks are at work to reduce what we are putting in (while others act to accelerate that change). The goal here is to get a feel for rates of change and playing with the simulations will help to illuminate your answers.

C-Learn simulation:  One of the most interesting interactive tools available to figure out the affects of CO2 input on climate is the C-Learn Climate Simulation . It gives you control of many things: Developed vs. Developing Country emissions, projected greenhouse gas emissions (start year/target year), emissions from deforestation, etc. You can do many model runs and then compare them in a number of different graphs (see top bar options). Quite neat. Note that when you start, all the emissions are set to very high levels (current rates of increase sustained: ‘Business As Usual’). Start out trying values where goals are to reduce emissions (not increase by 500%!). Perhaps play with different rates of response by the different country groups. It may help give you ideas of things to play with in the simulation by looking at the climate modelling/sensitivity pdf file (e.g. slides: 17, 19, 25, 27).

Note: These simulations are obviously not ‘the true actual climate reponse’. They aren’t real climate models at all (which require supercomputers to run), but are set up to use data from the IPCC modeling runs that are considered most likely. They are designed to give you a sense of climate response using reasonable parameters. The database/models chosen as being ‘most likely’ do tend to be at the conservative end of the range of models/assumptions/uncertainties. Negative feedbacks are quite well understood based on past climate change. New negative feedbacks would be a bonus as we move into a warmer thermal regime. Positive feedbacks are more difficult to predict as we move rapidly into a warmer climate. Uncertainties about positive feedbacks increase substantially when CO2 equivalent concentrations are greater than 450 ppm. Also, note that in all of these simulations as well as the IPCC models, the models are actually done using all greenhouse gases (not only CO2). Typically, the IPCC reports use the term “CO2 equivalent” to mean all GHG.

To access the C-Learn Model:

1.     Click on the link https://www.climateinteractive.org/tools/c-learn/

2.     Scroll down and read the ‘Instructions to Get Started with C-Learn’. There is also a video introduction which lasts a little over 10 minutes. It also tells you about what C-Learn can do. You will also find an FAQ section and more information on the assumptions used by the program, etc. if you wish to have a look at those files. You can poke around there as much as you like.

3.     Once you feel familiar with the program, click on ‘run c-learn’. You will need to make up a login name. Type ‘ciguest35’ or any number at the end that you like.

4.     Now you’re in, you can try out the various scenarios you find in the questions below as well as play around with as many others as you like. It is definitely a neat tool to try to help us really grasp the significance of our collective behavior on the planet!

(Questions)

1.      If things continue at ‘status quo’, what will the atmospheric CO2 concentration be by the year 2100? What will the average temperature increase be over preindustrial levels?

1)      476 ppm; 2.5 degrees Celsius

2)      612 ppm; 3.5 degrees Celsius

3)      908 ppm; 4.5 degrees Celsius

4)      210 ppm; 1.5 degrees Celsius

2.      If all things remain the same except we stop increasing the input of CO2 to the atmosphere now (year 2016), what will the atmospheric CO2 concentration be by the year 2100? What will the average temperature increase be when compared with preindustrial levels?

1)      464 ppm; 2.3 degrees Celsius

2)      503 ppm; 2.5 degrees Celsius

3)      606 ppm; 2.9 degrees Celsius

4)      437 ppm; 2.1 degrees Celsius

3.      If tree removal falls to 50% of its current level and the replanting of trees rises by 25%, and the carbon dioxide pollution stops growing and actually begins to decline by 4% in all countries this year (2016), the temperature increase in degrees by the year 2100 will be _______________. (***enter only the relevant number in the space provided – do not enter a unit).

4.      If tree removal falls to 50% of its current level and the replanting of trees rises by 25%, and the carbon dioxide pollution stops growing and actually begins to decline by 2% in all countries this year (2016), the temperature increase in degrees by the year 2100 will be _______________. (***enter only the relevant number in the space provided – do not enter a unit).

5.        If tree removal falls to 50% of its current level and the replanting of trees rises by 25%, and the carbon dioxide pollution stops growing and actually begins to decline by 2% in all countries by the year 2025, the temperature increase in degrees by the year 2100 will be _______________. (***enter only the relevant number in the space provided – do not enter a unit).

6.        If tree removal falls to 50% of its current level and the replanting of trees rises by 25%, and the carbon dioxide pollution stops growing and actually begins to decline by 4% in all countries by the year 2025, the temperature increase in degrees by the year 2100 will be _______________. (***enter only the relevant number in the space provided – do not enter a unit).

7.        If tree removal remains at 50% of its current level and the replanting of trees rises by 25%, and the carbon dioxide pollution stops growing and actually begins to decline by 2% in all countries by the year 2036 (20 years from now), the temperature increase in degrees by the year 2100 will be _______________. (***enter only the relevant number in the space provided – do not enter a unit).

8.      The current levels of CO2 are approaching 400 ppm. Lets assume CO2 concentrations in the atmosphere are stabilized at 450 ppm by the end of this century (2100) [you can play with C-Learn to create that kind of scenario in various ways].  If the best current understanding of the climate system is correct in terms of the influence of greenhouse gasses on temperature, is the increasing global average temperature stabilized by 2100? Explain why/why not.

Hint: Notice the tab for ‘temperature’ in the top right of the C-Learn window where you can see the affects of your current run on temperature.