6 Lab 6: Climate Change Modeling
Introduction
There is scientific consensus among climatologists that the current changes to the Earth’s climate system are predominately caused by human activity. The generation of fossil-fuel-derived energy has greatly shaped global civilization and allowed for substantial advancement and prosperity. However, it has come at a price. The unintended biproduct of fossil-fuel-derived energy is the release of various carbon-based gases that alter the chemistry of the atmosphere. Increasing concentrations of these greenhouse gases in the atmosphere increases their effectiveness at absorbing and in-turn releasing thermal energy. The more greenhouse gases in the atmosphere, the more thermal energy that stays in the climate system, and the warmer conditions become. The purpose of this lab is to experiment with greenhouse gases and temperatures through a simple model.
The objectives of this lab are to:
- Examine evidence of the impact atmospheric carbon dioxide has on Earth’s global average temperature
- Develop a physical connection linking carbon dioxide in the atmosphere and fossil-fuel-based emissions
- Design and test a scenario of climate change
Background Information/Further Reading
Climatic Change
Since the 1880s, the average global temperature of the planet has warmed by approximately 1.2 °C (about 2.5 °F). This warming has also led to a wide-array of other changes, such as the acidification, warming, and rising of global oceans, the decrease in the spatial extent and mass of snow, ice, and glaciers, and the increase in extreme precipitation and drought frequency. Such changes have impacts on nearly every aspect of society and the environment, though not all are negative at an individual level. For those interested, a very detailed report is available from the Intergovernmental Panel on Climate Change (IPCC): https://www.ipcc.ch/report/ar5/syr/.
Greenhouse Gases
The predominant cause of current climatic change is due to human-input of greenhouse gases into the atmosphere. Gases such as carbon dioxide, methane, nitrous-oxide, and others are bi-products of combustion reactions which generate energy for human needs. These gases however, are exceedingly efficient at ‘trapping’ thermal energy (aka heat) from entirely escaping out to space. In moderation, greenhouse gases are very important to keeping the planet livable. Without them, the average temperature of the planet would be approximately -18°C, well-below the freezing point of water. However, with too high a concentration of greenhouse gases, excessive amounts of thermal energy (heat) are retained within the climate system, increasing the temperature. The most robust observations of carbon dioxide have occurred at the Mauna Loa Observatory in Hawaii, which has tracked the concentration in the atmosphere since the 1950s. Below, you’ll see the “Keeling Curve” or a monthly timeseries of CO2 concentration. Note the increasing trend in the timeseries.
Perspectives of Change
A variety of robust evidence strongly indicates that human activity is the cause of the planet’s current warming. While temperatures have fluctuated in the past, the rate at which it currently is increasing is unparalleled in the last 2000 years (https://www.europeanscientist.com/en/environment/ongoing-extent-of-global-warming-is-unparalleled/). Keep in mind how human civilization has flourished during that window, and human populations were either minimal, or non-existent, during previous hot/cold periods in Earth’s geologic past.
Climate Modeling
While observations are necessary for documenting change, if we are curious about what the future might hold, models are needed. Because observations from the future just don’t exist yet, models allow for an educated evaluation of what the future might hold. In climate modeling, extensive mathematical and physics-based equations are used, which are based on the fundamental understanding of things like winds, ocean currents, nutrient cycles, physics, plant growth, thermodynamics, and others. There are so many different equations that are calculated and solved over and over again, that climate models often require supercomputers.
In this lab, we will be using a very simple climate model, one that will easily run on your own [Flash player-enabled] computer, to evaluate the linkages between carbon dioxide and temperature. It is called the “VERY, VERY SIMPLE CLIMATE MODEL”. https://scied.ucar.edu/simple-climate-model Due to its simplistic nature, this model does not account for other greenhouse gases, cycling of carbon into other spheres such as the oceans or biosphere, changes of land use, and wind/precipitation patterns.
The model assumes, based on extensive evidence, that temperature rises approximately 3°C for each doubling of carbon dioxide concentration. Additionally, the starting values for the model are appropriately equal to what they were in real life in the year 2000. If you’d care to explore, mathematically, the formula used by the model is:
For reference, every 2.3 gigatons of carbon dioxide emissions should raise the atmospheric carbon dioxide concentration by approximately 1.0 part per million.
Questions
1. Prior to doing anything else, it is important to actually think about what the model might show us. What is the model able to show? What is it not able to show?
2. What, if any, are the uncertainties or limitations of using such a model?
3. Examining the model output graph (still without running an experiment), describe what the various axes are (x-axis and 3 y-axes).
Part 1 – Trial Experiment
4. The default baseline emissions of CO2 are 10.5 GtC per year. According to the model, what would the Earth’s temperature be in 2100 if we released the same amount of carbon dioxide into the atmosphere each year as the baseline?
5. What is the global concentration of CO2 in 2100 from the experiment in #4?
6. Rerun the experiment (by clicking “start over”), but this time decrease the timestep to 1 year. Are the results any different? What does the timestep variable do?
Part II – Developing a Scenario
7. Do you think the experiment from part 1 is a realistic scenario of what people will actually do over the 21st century in terms of emissions? Why or why not.
8. Think about how (and why) carbon emissions might change into the future. What all do you need to consider to predict how much carbon will be emitted?
9. How do you think carbon emissions will change into the future? You’ll share a more detailed outline in question 10, but for now, generalize in a sentence or two.
10. Fill out the top row of the table below with your carbon emission scenario. Then run the model using your develop scenario. Keep in mind, the amount of emissions can change at every time step, if you want them to. A 10-yr timestep is shown for ease of use.
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2050 |
2060 |
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2080 |
2090 |
2100 |
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CO2 emissions
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Resulting temperature
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Resulting CO2 concentration
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11. What happened to the climate in your developed scenario?
12. Refresh the page and run an experiment where the emissions are zero moving forward. How does the climate change, both temperature and CO2 concentration?
13. Is this a realistic experiment given the limitations and constraints of the model? How so?
