Extreme Weather

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 

You will recall from what you learned in Lab 5B that one of the key indicators of climate change is the steady upward trend in global temperature, depicted in the graph pictured to the left.

To begin your investigation, read the NASA Earth Observatory's article 2020 Tied for Warmest Year on Record.

In the temperature graph, on the NASA page, focus on the temperature during the past 60 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 

Keeping the NASA temperature graph in mind, observe the graph of CO₂ from Mauna Loa Observatory, shown here. The Mauna Loa graph is from 1960 to present, during which time scientists have carefully monitored and measured CO₂ concentrations in the atmosphere. The red line in the graph is the monthly data and the black line is the trend for the year.

How, when, and why did scientists begin to monitor CO₂ in the atmosphere and what have we learned from these observations? Watch 'CO₂ and the Atmosphere' 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.

Evidence of a changing climate on varying time scales

In 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.

1. First, study the long-term CO₂ data shown in the graphic below, and consider the question: How is the recent—since 1950—trend in CO₂ different from other cyclical variations in CO₂ concentrations; ones that took place over the past six hundred thousand years?
2. 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? Visit UCAR's Very Simple Climate Model page to view the interactive and set up some experiments.

1. 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.
2. In the year 2000, 7.79 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.
3. When you have chosen your settings, click the Step Forward button (to the left of the Play button) to see how temperature and CO₂ change in 5-year increments. Click the Step Forward button until the graph has filled to the year 2100.
4. When you have finished exploring answer the Checking In questions below.
   Show me more about the graph
   Hide
   What does the graph mean? 
   Blue dots (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 7.79 Gigatons of CO₂ into the atmosphere. 
   
   Black triangles (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 369.52 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 14.4° C in the year 2000. In this simple model, temperature is based entirely on the atmospheric CO₂ concentration
   
   

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 from the list a city near your home location. The cities on this list that are highlighted in blue 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.

1. Once on the new page, choose the following parameters:
   • Parameter: Average Temperature
   • Time Scale: Annual
   • Start Year: 1895 (or the oldest year your city has data for)
   • End Year: Present (i.e. 2020)
   • 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"
2. 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.
3. The computer will generate a graph of the data for your city. The violet line is the actual recorded average or mean temperature for the year, the gray 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 135 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 1951-1980, while areas that are orange or red are above the baseline average.

Source: NASA GSFC
 
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.

Optional Extension

View this NY Times Interactive graph to see the 2015 climate trends in three thousand cities worldwide.