Part C: Global Temperature Change
In the previous lab you explored some of the indicators of climate change and you viewed graphs showing the rates of change in the selected indicators. In this lab, you will get a better sense of how rapidly the most recent century-scale changes in global temperature are taking place as compared to past millennial-scale changes. You will gain a better understanding of the interrelationship between global temperatures and atmospheric concentrations of the greenhouse gases, especially carbon dioxide. And, you will view satellite maps showing the spatial patterns of global warming over the past 150 years.
Global temperature trends
To begin your investigation, click on the image, left, to view a flash interactive on a new page. On the interactive, rollover the blinking points to learn more about some events that have affected our planet's climate. Use information given in the graphic to answer the Checking In questions below. When you are done viewing the interactive, use the back button in your browser to return to this page.
In the temperature graph, pictured above, focus on the temperature during the past 50 years, 1960 to present. During this time period, the trend shows significant warming. In the next section of the lab you will investigate a parallel trend, that of carbon dioxide.
Trends in carbon dioxide concentrations
How, when, and why did scientists begin to monitor CO2 in the atmosphere and what have we learned from these observations? Watch the CO2 and the Atmosphere (9:03 minutes), to learn how scientists investigate and record changing levels of CO2 as well as other records of climate change. As you are watch this video, keep the following Stop and Think questions in mind.
Stop and Think
- Why did the U.S. Air Force study water vapor and CO2 in the atmosphere? What did they learn?
- What happens if you remove CO2 from the atmosphere? How do we know?
- How do glaciers record the temperature and CO2 concentration of Earth's atmosphere?
- What is happening to glaciers worldwide? How is this an indication of climate change?
- List three natural causes of variation in Earth's climate that were mentioned in the video clip.
Evidence of a changing climate on varying time scalesIn the next section of this lab, you will explore how recent changes compare to long-term changes and you will look more closely at the relationship between CO2 and temperature.
- First, study the long-term CO2 data shown in the graphic below, and consider the question: How is the recentsince 1950trend in CO2 different from other cyclical variations in CO2 concentrations; ones that took place over the past six hundred thousand years?
- Next, compare the trends in global temperature (shown below in red) with the changing levels of CO2 (in blue) on the graphic. Note how the two graphs rise and fall together. According to the data shown below, and referenced in the video, there is a correlation between CO2 concentrations in the atmosphere and global temperature.
Model the effect of CO2 concentration on global temperature
Ready to extend your knowledge and try your hand at modeling? Use the following interactive to set up some experiments.
Source: Climate model interactive developed by Randy Russell, UCAR. Used with permission.
- First, explore the interactive using the preset CO2 emissions rate and time step size. Click Start Over to change the variables and investigate the relationship between CO2 and temperature.
- In the year 2000, 6 Gigatons of CO2 was released into the atmosphere. Discover what might happen to temperature if we increase our rate of emissions. Decide how much CO2 will be released into the atmosphere each year and set the CO2 emissions rate.
- Next, adjust the Time step size depending on how far you want the model to move into the future with each click.
- When you have chosen your settings, click the Step Forward button to see how temperature and CO2 change. Click Step Forward until you've filled the graph to the year 2100.
- When you have finished exploring answer the Checking In questions below. What does the graph mean?
Blue triangles (and blue y-axis scale) indicate the emissions of CO2 in the atmosphere each year. This is measured in Gigtatons of CO2 (GtC) per year. In the year 2000, we released 6 Gigatons of CO2 into the atmosphere.
Black dots (and black y-axis scale) show how much carbon dioxide has built up in the atmosphere over time. This is measured in parts per million by volume (ppmv). The actual amount was around 368 ppmv in the year 2000.
Red squares (and red y-axis scale) shows average global temperature in degree Celsius. For reference, this value was around 14.3° C in the year 2000. In this simple model, temperature is based entirely on the atmospheric CO2 concentration
- What happens to the average global temperature as you increase the concentration of CO2 in the atmosphere? As you increase the concentration of CO2 in the atmosphere the average global temperature also increases.
- How do the slope of the temperature and CO2 concentration lines change as you increase the emission rates? As you increase the emission rates of CO2 the slope of the other lines both increase. This is because you are compounding the amount of CO2 in the atmosphere.
Consider temperature trends in your local area
You are probably curious: What has been the trend in average temperatures in your own local area during the past 50 years?
To find out the answer to this question, access the National Climate Data Center (NCDC) U.S. Cities Analysis and choose a city near your home location. You can either choose from the map, or from the list on the left of the map. The cities on this list, and in blue on the map, are part of the U.S. Historical Climate Network. (USHCN). These cities have been selected because they are representative of their region's conditions, have a complete record of data, and have been corrected for any station changes or other potential errors in the data.
- Once on the new page, choose the following parameters:
- Parameter: Temperature
- Time Scale: Annual
- Start Year: 1895
- End Year: Present (i.e. 2013)
- State: Your state of choice
- Climate Division/City: Your city of choice
- Leave the Base Period Years set to the defaults
- Select "Display Trend per Decade"
- When you have set the parameters, click the Plot button. It is located below the settings boxes. You may need to wait a few minutes for the graph image to load.
- The computer will generate a graph of the data for your city. The red line is the actual recorded average or mean temperature for the year, the black line is the average of all the years combined, and the blue line shows the trend in average temperature over time. Above the graph you will find the values for average temperature, and the trend (in degrees F per decade) for the time period that you selected. Explore several time periods at one station, and several locations to see how the trend varies across the conterminous (lower 48) United States. If time allows, explore several locations and time periods of your own choosing.
Are all areas of Earth warming at the same rate?
As you saw when comparing the graphs of the U.S. Historical Climate Network, the trend in temperature varies by region, due to many factors. In this section, you will gain an even larger vision of how surface temperature anomalies vary year to year across the globe. The video, produced by NASA, shows 132 years of global warming, as reconstructed from instrumental records, satellite data, and models.
Before viewing, use the legend, located at the bottom-right of the map, to gain an understanding of what the map is showing you. Areas that are colored blue are below the baseline temperature, for the period 1880-1950, while areas that are orange or red are above the baseline average.
Optional: For more information about the video, or for an alternate way to view the video (without YouTube), access this article: NASA article
Play the video several times, pausing it at years of your interest. Note how the temperature patterns move around from year to year. Describe patterns that you see in the data. Some years are colder than average and some warmer. However, as you can see, the overall change in warming accelerates during the most recent 50 years. After watching the video answer the Checking In questions below.
In the final part of Lab 5, you will extend your understanding of global temperature trends and climate change by learning more about computer models and projections for future temperature and precipitation patterns.