Part D: Climate Models: What does the Future Hold?
In the previous labs, you investigated the global and U.S. temperature records for the past 50 years. You learned about the likely causes of these changes in the global climate and the observed indicators of climate change. Additionally, you shared examples of extreme weather events. In this lab, you will now look forward in time by learning about climate models and viewing the projected changes in climate for the upcoming century.
What are climate models, and how do they work?
Climate models are constructed using basic physical equations describing how the climate system works in three dimensions, as pictured in the graphic, right. This means equations must be included that describe the Earth system and its processes, such as the ocean, the atmosphere, the land, hydrologic and cryospheric processes, terrestrial and oceanic carbon cycles, and atmospheric chemistry. Unlike weather forecasting models, which are constantly updating with changing real-time data and describe the daily sequence of environmental conditions starting from a present state and working forward in time (to as far as a week with some reliability), climate models are based on the physics and chemistry of the Earth system to describe the average conditions in the future.
To complete a climate model, the physical equations, which represent how the spheres interact, are coupled with scenarios (described below) of how Earth's human population, land use, and economy could evolve. Once a climate model is run, the model output data is compared with the observed data from the past. This process allows scientists to check the accuracy of the models.
Watch this brief video from the Australian science agency CSIRO for an explanation of climate models:
Worldwide, various teams of scientists have modeled climate change and the subsequent impacts to the year 2100 and beyond. While the models show that rising global temperatures generally characterize the future world, human behavior will determine how dramatic the changes may be.
What is a scenario?
A scenario is an image of a potential future that is based on historical knowledge and expectations of future change. The IPCC scenarios are based on a data-driven pathway (or narrative) of what events have occurred in the past and how the future may unfold.
The scenarios describe the relationships between the forces driving greenhouse gas and aerosol emissions and their potential future change during the 21st century for the globe. The most recent models also include pathways representing different projections of a set of influential socioeconomic factors, including population growth, technological development, economic development, and their associated energy, land use, and emission implications.
Shared Socioeconomic Pathways (SSPs) look at projected global socioeconomic changes until 2100. These scenarios consider possibilities for countries globally and how each may choose to approach their future socioeconomic development. There are five narratives that consider a range of possibilities.
Representative Concentration Pathways (RCPs) looks at possible future greenhouse gas emissions. The numbers in the RCPs stand for the amount of radiative forcing a difference to Earth's energy balance, which results in either warming or cooling (measured in watts per meter squared or W/m2) that the atmosphere will reach before leveling off. As the radiative forcing is caused primarily through the rise in greenhouse gases, the number will, therefore, also correspond to a concentration of GHGs in the atmosphere. In order to simplify calculations, all of the GHGs have been given a CO2 equivalency (CO2e) for modeling.
SSPs + RCPs = SSP Scenarios
By combining the SSPs and RCPs, a number of combined scenarios are possible. However, because the SSPs have assumed certain future socioeconomic trajectories, there are RCPs they cannot easily match withfor example, SSP1, which is focused on sustainability, will not match with RCP8.5's high emissions pathway; similarly, RCP1.9, which has very low emissions and would require consensus building, can't match with SSP3, which models a socioeconomic pathway of rivalry between countries that don't work together. These assumptions helped scientists to narrow their focus to models using five different combined scenarios.
According to the IPCC, the five combined scenarios (in white text in image at right) have been designed to span a wide range of possible future conditions, including a no-additional-climate-policy scenario of SSP3-7.0, and a strong mitigation scenario with SSP1-1.9. The scenarios don't try to forecast how events will happen in the future or account for the impact of climate change on the SSPs, nor do they try to prove which, if any, is more likely than another.
What do the models predict for future temperature?
View the graphs below, from the IPCC Summary for Policy Makers. The five scenarios diagrammed in the graphic are identified as high (SSP5-8.5, SSP3-7.0), intermediate (SSP2-4.5) and low (SSP1-2.6, SSP1-1.9) GHG emissions. The left panel in the graph shows CO2 emission rates in gigatons per year. The graph on the right shows the global surface warming 1950-2015 as well as the predicted future to 2100, based on projected emissions. Note that the range of emissions varies depending on the scenario, which you learned about in the beginning of this lesson. As you are viewing the graphic, answer the Checking In questions below.
- Looking at the graph, which of the scenarios produces the most rapid increase in CO2 and temperature?
- Looking at the graph, which of the scenarios produces the least rapid increase in CO2 and temperature?
Next, look at the maps of modeled global temperature and precipitation change alongside of the projected temperature graphs. Click an image to enlarge it for a better view.
- First, focus on the maps. Compare the maps of the three simulated temperature increases, 1.5 °C, 2 °C, and 4 °C. Which scenarios are likely to produce the temperature/precipitation increases, and if so, by when?
- On the temperature map for 4 °C, how many degrees of change occurs in northern Eurasia (Russia) compared with southern South America (Argentina) ?
View and compare model outputs
Now that you have some familiarity with climate models, including how models are developed and how they may vary, you will observe several climate models on the IPCC's WGI Interactive Atlas website.
1. To begin, go the the WGI Interactive Atlas website. Start by looking at the spinning model of the globe labeled "Our Possible Climate Futures" on the right of the homepage. The globe will be showing a temperature model, which will be indicated by the information highlighted in blue, such as +2 °C and Temperature. You should see four different temperature options.
2. Click +1.5 °C and take note of the different shades of red on the global map. The darker shades of red indicate a greater (and lighter shades of red indicate a smaller) difference in temperature, or anomaly, from the 1850-1900 baseline or average.
3. Next, click through and note the differences with each of the other temperature outcomes as well. (Optional: do the same for each temperature on the precipitation maps.) This model uses the multi-model mean, which is the average of the climate models that have run.
4. Find the box below and left of the globe, labeled Regional Information. Click the lower right corner of this box to access the Advanced version of the climate models the temperature data is based on.
On this web page you can select IPCC model datasets and view their output. Begin by selecting one multi-model mean.
5. On the toolbar above the map, hover over or click Dataset. Make sure that in the Model Projections column, the CMIP6 radio button is selected.
6. Next, hover over or click Variable in the toolbar. Beneath Atmosphere select Mean Temperature (T).
7. Hover over or click Quantity & Scenario in the toolbar. Confirm that beside Quantity, Change is selected. Then select Period: Long-term (2081-2100). and Scenario: SSP1-2.6. Confirm that the Baseline remains 1850-1900 to be consistent with the other data you've looked at.
Note that the selected parameter information shows up below the map along with how many models were used to determine the mean.
8. Move your mouse over the map to highlight different regions. The temperature slider on the left will adjust, indicating the temperature beneath the mouse cursor.
9. Click the region that contains your hometown. This will bring up a series of graph options at the bottom of the page.The Time Series graph shows the modeled temperatures 1950-2014 in gray and 2015-2100 in blue. The gray shaded box indicates the time period currently mapped. Take notes of the graph and the data. When you're done, click the X in the upper right of the graph area to close it.
10. Select a different region on the global map where you would like to live someday. Click on that region and make notes of the Time Series graph and data and compare differences.
- What does the dark gray to dark blue line on the Time Series graph indicate?
11. Now, you're going to change a single parameter (variable) on your map. Here are some changes to consider:
Scenario - different SSP
Atmosphere - Total precipitation, Snowfall, Frost Days
Period - time frame of the model: Near, medium, or long term
12. Look at the globe as well as the same two areas of the map you selected before and note the changes.
13. Change the same parameter you adjusted in Step 11 to a different option. Make note of changes globally and in the same two regions you have looked at before.
Stop and Think
- What regions of the Earth warm most dramatically in all of the climate models shown in the IPCC Atlas?
- Describe your general observations about the differences in the the maps of the two places you chose to view. Write about similarities or differences and what changes, if any, happened when you adjusted your parameter. (Be sure to note what parameters you had and which one was changed.)
- On the IPCC Atlas website, choose your own starting variables. Describe your choices, then compare and contrast the model outputs. If possible, save copies of the maps, and insert them in your report.
Try a climate and energy questionnaire
How would you change the world?
Read the article to the 9-question interactive, and answer the interactive's questions. Keep in mind that each choice you make will have costs for both the climate and for the pocketbooks of people under the policies. After you have completed the questionnaire, you will see a projection of climate and energy costs (from 2019 to 2100) based on your choices. Repeat the questionnaire several times and compare your results.
How did your choices affect the outcome?
Note: The black line in the results incorrectly labeled "Business as usual" depicts the high-emissions RCP8.5.
How do energy choices influence global climate change? Can one person really make a difference? Brainstorm and share ideas for changes in your lifestyle that you and your classmates (and families) can make.
Learn more about CO2e - CO2 Equivalents and global warming potential (GWP)
You can learn more about climate models, especially how they are constructed and used, by downloading and reading this PowerPoint presentation file What is Climate Modeling? (PowerPoint 2007 (.pptx) 6.3MB Jun20 11) from NOAA's presentation library.
Climate Modeling 101 presents a detailed explanation of climate models and how they are similar to and different from weather models.