Extreme Weather

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:

Climate Modeling from CSIRO

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 21^st 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.

Optional: more details about SRES and older scenarios

Older IPCC reports used scenarios, known as SRES, that incorporated both emissions and socioeconomic elements into single scenarios. These SRES scenarios (which went by storyline names A1, A2, B1, B2, A1Fi) were too broad and difficult to fine tune with updated data. Later, the IPCC separated these two elements into separate pathways, known as RCPs and SSPs, which allowed scientists to clarify different emissions pathways and different socioeconomic pathways independently. However, SSPs scenarios were not completed in time for the 2013 IPCC report (AR5), so most pathway scenarios prior to 2020 will show only RCP pathways. Both RCPs and SSPs were first combined for complete modeling scenarios for the IPCC's AR6 report in 2021.

SSPs

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.

Optional: more details about SSP Narratives

Note: SSP narrative summaries here are from Table 2 in Riahi et al, 2017

SSP1 Sustainability

SSP1 Sustainability – Taking the Green Road (Low challenges to mitigation and adaptation)

The world shifts gradually, but pervasively, toward a more sustainable path, emphasizing more inclusive development that respects perceived environmental boundaries. Management of the global commons slowly improves, educational and health investments accelerate the demographic transition, and the emphasis on economic growth shifts toward a broader emphasis on human well-being. Driven by an increasing commitment to achieving development goals, inequality is reduced both across and within countries. Consumption is oriented toward low material growth and lower resource and energy intensity.

SSP2 Middle of the Road

SSP2 Middle of the Road (Medium challenges to mitigation and adaptation)

The world follows a path in which social, economic, and technological trends do not shift markedly from historical patterns. Development and income growth proceeds unevenly, with some countries making relatively good progress while others fall short of expectations. Global and national institutions work toward but make slow progress in achieving sustainable development goals. Environmental systems experience degradation, although there are some improvements and overall the intensity of resource and energy use declines. Global population growth is moderate and levels off in the second half of the century. Income inequality persists or improves only slowly and challenges to reducing vulnerability to societal and environmental changes remain.

SSP3 Regional Rivalry

SSP3 Regional Rivalry – A Rocky Road (High challenges to mitigation and adaptation)

A resurgent nationalism, concerns about competitiveness and security, and regional conflicts push countries to increasingly focus on domestic or, at most, regional issues. Policies shift over time to become increasingly oriented toward national and regional security issues. Countries focus on achieving energy and food security goals within their own regions at the expense of broader-based development. Investments in education and technological development decline. Economic development is slow, consumption is material-intensive, and inequalities persist or worsen over time. Population growth is low in industrialized and high in developing countries. A low international priority for addressing environmental concerns leads to strong environmental degradation in some regions.

SSP4 Inequality

SSP4 Inequality – A Road Divided (Low challenges to mitigation, high challenges to adaptation)

Highly unequal investments in human capital, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over time, a gap widens between an internationally-connected society that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor intensive, low-tech economy. Social cohesion degrades and conflict and unrest become increasingly common. Technology development is high in the high-tech economy and sectors. The globally connected energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but also low-carbon energy sources. Environmental policies focus on local issues around middle and high income areas.

SSP5 Fossil-fueled Development

SSP5 Fossil-fueled Development – Taking the Highway (High challenges to mitigation, low challenges to adaptation)

This world places increasing faith in competitive markets, innovation and participatory societies to produce rapid technological progress and development of human capital as the path to sustainable development. Global markets are increasingly integrated. There are also strong investments in health, education, and institutions to enhance human and social capital. At the same time, the push for economic and social development is coupled with the exploitation of abundant fossil fuel resources and the adoption of resource and energy intensive lifestyles around the world. All these factors lead to rapid growth of the global economy, while global population peaks and declines in the 21st century. Local environmental problems like air pollution are successfully managed. There is faith in the ability to effectively manage social and ecological systems, including by geo-engineering if necessary.

RCPs

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.

Optional: more details about RCP Narratives

Since 2013, when four RCPs were modeled, the IPCC has expanded their RCPs total to seven (from high emissions to low): 8.5, 7.0, 6.0, 4.5, 3.4, 2.6, 1.9. Of these seven, five were chosen to focus on for the most recent IPCC report (AR6).

RCP8.5: energy-intense growth pathway with >8.5 W/m² by 2100

RCP7.0: growth with high CO₂ and non-CO₂ emissions, including aerosols

RCP4.5: leveling off of emissions mid-century

RCP2.6: emissions peak and begin to fall starting early in 21st century, implied net zero emissions in the second half of the century.

RCP1.9: this RCP was created in order to model the 1.5C of warming by 2100 allowed by Paris Climate agreement; implied net zero emissions around the middle of the century.

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 with—for 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.

Checking In

Looking at the graph, which of the scenarios produces the most rapid increase in CO₂ and temperature?
Show me the answer
Looking at the graph, which of the scenarios produces the least rapid increase in CO₂ and temperature?
Show me the answer

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.

Checking In

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?
Show me the answer
On the temperature map for 4 °C, how many degrees of change occurs in northern Eurasia (Russia) compared with southern South America (Argentina) ?
Show me the answer

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.

Show me how

On this web page you can select IPCC model datasets and view their output.

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.

Show me how

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.

Show me how

Note that the selected parameter information shows up below the map along with how many models were used to determine the mean.

Show me what it looks like

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 about 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 learn about. Click on that region and make notes about the Time Series graph and data and compare differences.

Checking In

What does the dark gray to dark blue line on the Time Series graph indicate?

Show me the answer

11. Now, you're going to change a single parameter (variable) on your map. Here are some changes to consider:

Under Quantity and Scenario: Scenario, select a different SSP

Under Quantity and Scenario: Period, change to Near Term (2021-2040) or Medium Term (2041-2060)

Under Variable: Atmosphere, select Total Precipitation (PR), Snowfall, or Frost Days (FD)

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 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 used 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?

Visit the 2019 article Choose your own climate energy adventure, which talks about the En-ROADS climate simulator.

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.

Discuss

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.

Optional Extensions

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.

Show me the presentation in PDF form

Climate Modeling 101 presents a detailed explanation of climate models and how they are similar to and different from weather models.

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