Graphing Global Temperature Trends
This activity is related to a Teachable Moment from April 12, 2017. See "Celebrate Earth Day with NASA Science Data"
In this activity, students will use global temperature data to create models and compare short-term trends to long-term trends. They will then determine whether global temperature is rising based on the data.
Note: This activity is aligned to education standards for fifth grade and high school grade bands. As such, we have provided two sets of procedures, one for grade five and one for high school. Other variations for each grade band are indicated throughout the activity.
- The data file for this activity contains 137 years of average global annual temperature measurements. Depending on class size, the steps in “Procedures” can be done by individuals or groups of students.
- Divide the data so that each group or individual has approximately the same number of data points.
- For students just learning to graph points, use the pre-labeled graphing worksheet. Help more advanced students determine an appropriate vertical scale to use on quadrille-ruled graph paper. Determine the range of data by subtracting the maximum and minimum temperature values (e.g., 14.87-13.54=1.33). Placing the graph paper in portrait orientation allows for approximately 40 lined intervals. Determine scale by asking which place value (ones, tenths, hundredths, etc.) should be used. Demonstrate that counting by ones on each line will not allow for accurate resolution of data. Have students determine how many lines they will need if they count by tenths and if they count by hundredths.
- Have beginning graphing students label the horizontal axis of the graphing worksheet with the years their data encompasses. Help advanced students determine an appropriate horizontal scale to use on the quadrille-ruled graph paper. It is important to evenly space the years. The group that has the most years of data to graph will determine the scale that all groups will use.
- Monitor students closely while they are plotting data points to be sure they are using a consistent scale. A consistent scale allows data to be combined seamlessly and accurately.
- When combining individual graphs into the class graph, be sure to fold back or cut off extra paper so that the year spacing remains constant throughout the graph.
Grade 8 and High School
- The data set for this activity contains 1,644 monthly data points presented in a single file that students can use to make and manipulate their own graphs. If students are unfamiliar with spreadsheet software, have them create their own graphs while following along as the instructor shows them the steps.
- After accurate graphs have been constructed and the discussion has concluded, give students some time to explore how the graphs could be manipulated and therefore misconstrued by a casual observer.
Scientists have concluded that our climate is changing, that global temperatures are on the rise, and that there are serious consequences to these rising temperatures. But in an age of plentiful yet opposing information, how do students separate fact from fiction? Simple: Examine the source data and do the math.
Weather and climate are two frequently confused terms that refer to events with broadly different spatial and time scales. Weather refers to atmospheric conditions that occur locally over short periods of time – from minutes to hours or days. Familiar examples include rain, snow, clouds, winds, floods or thunderstorms. Remember, weather is local and short-term. Climate, on the other hand, refers to the long-term regional or even global average of temperature, humidity and rainfall patterns over seasons, years or decades. Climate is regional or global and long-term; weather is local and short-term. Erratic weather in your neighborhood – whether rain or drought – may or may not be a symptom of global climate change. To know, we must monitor weather patterns over many years.
Two other terms that are often incorrectly used interchangeably are “global warming” and “climate change.”
Global warming refers to the upward temperature trend across the entire Earth since the early 20th century – and most notably since the late 1970s – due to the increase in fossil-fuel emissions since the beginning of the Industrial Revolution. Though there are many different greenhouse gases, carbon dioxide, or CO2, is the one that has been on the rise during the last century. Since the beginning of the Industrial Revolution, the concentration of CO2 in the atmosphere has increased by 39 percent. Increasing the concentration of greenhouse gases causes the Earth greenhouse to overheat. Worldwide since 1880, the average Earth surface temperature has gone up by about 1.4 degrees Fahrenheit (0.8 degrees Celsius) relative to the mid-20th-century baseline (measured between 1951 and 1980).
Climate change refers to a broad range of global phenomena created predominantly by burning fossil fuels, which add heat-trapping gases to Earth’s atmosphere. These phenomena include the increased temperature trends described by global warming, but also encompass changes such as sea-level rise; ice-mass loss in Greenland, Antarctica, the Arctic and mountain glaciers worldwide; shifts in flower and plant blooming; and extreme weather events.
Climate change is driven by an increase in global temperature. But how do we know global temperatures are on the rise? We analyze temperature data, including daily temperature readings and monthly or annual average temperatures. The longest running record of directly measured temperature is the Central England temperature data series starting in 1659. The longest-running global record starts in 1880. Data are obtained from land stations and ships around the globe. More recently, satellites are used to measure temperature in the troposphere – the lowest level in our atmosphere. It is possible to derive temperatures prior to the dates of these modern records by studying polar region ice cores and ocean sediment cores. Ice cores store records of millennia of climate data. Using ice cores, scientists have reconstructed climate data for the last 750,000 years, showing seven ice ages, each interspersed with a warm interglacial climate like our climate today. (The difference between those interglacial periods and today is the increased rate at which the climate is changing – a rate that is directly related to the presence of humans and increased greenhouse gases in the atmosphere.) Ocean sediment cores add more data to the puzzle by way of marine fossils and sedimentary layers. Isotopic oxygen in marine fossils gives us information about ocean temperatures when the fossils were formed, and sedimentary layers provide data about historical events such as volcanic eruptions.
This activity allows students to examine real science data and draw their own conclusions about trends in global mean temperature.
Note: Global temperature data are reported as anomalies, the measure of the amount of departure from a reference value or long-term average. A positive anomaly indicates that the observed temperature was warmer than the reference value. A negative anomaly indicates that the observed temperature was cooler than the reference value. Anomalies more accurately describe climate variability over larger areas (that may have very different absolute temperatures) than absolute temperatures do. They also give a frame of reference that allows for more meaningful comparisons between locations and more accurate calculations of temperature trends. For better conceptual understanding, students may calculate absolute temperature from anomalies by adding the reference value to each anomaly. For elementary school students, the global annual mean temperature data set is reported as absolute temperature for simplicity.
- Explain to students that they will be analyzing average temperatures measured on Earth for the past 136 years, but each group will only be looking at a portion of that data.
- Distribute the global temperature data, either as a whole set or pre-divided for individuals or groups.
- Distribute graph paper or graphing worksheet.
- Explain to students that this is a large data set so, to streamline the activity, each group will graph a subset of the points. Then, the class will combine all the graphs into one to represent the entire 136-year trend.
- Call out each of the date ranges to verify that each one is assigned to a group of students.
- Tell students that because their graphs will be combined with the graphs from the rest of the class, everyone must use the same horizontal and vertical scale.
- Ask students to examine the data and determine which value, year or annual mean temperature, should go on the vertical axis. Although it can be done either way, annual mean temperature should go on the vertical axis for ease of viewing.
- Lead the students through the process of determining appropriate vertical and horizontal scales for their graph. Include a discussion of whether to orient their graph paper in a portrait or landscape manner. Portrait will provide more room for a precise vertical scale and allow for plenty of room for equally-spaced years on the horizontal axis. See the “Management” section for teaching suggestions.
- When all graph axes are labeled and teacher-approved, have students proceed with plotting their data points. Instruct students to make their data point dots large and dark so they will be visible when their graph is held up for the class.
- When individual graphs are complete, have students determine if they see an increase or decrease in mean global temperature for their group’s time frame. Discuss the risk of making climate assumptions and projections when looking at a small data set.
- Have students tape their graphs to the whiteboard and line them up horizontally, by year, maintaining equal spacing between all the years. (Fold or cut the graph paper as needed to remove empty spaces and align the data).
- Have students stand back and assess the trend. Is there a trend of global temperature increase or decrease?
- Ask students if this trend has always been the case over the past 136 years? If not, when did the trend shift?
- Have students guess why the trend shifted, then have them research the years when the trend shifted.
- Have students predict global temperature means for the subsequent year. Research this data on the Internet to compare.
Grade 8 and High School
- Ask students what they know about global temperature trends. Expect to hear differing opinions and perhaps the beginning of a heated debate, depending on the knowledge base of your students.
- Ask if any students have ever looked at global temperature source data (data measurements from science institutions) themselves. Expect that some students will say they have seen graphs. If they do, ask them if they know whether the graphs represent all available data and what the source of that data is.
- Discuss with students the importance of analyzing data, carefully scrutinizing graphs themselves and drawing their own conclusions rather than relying on sources that may not be factual.
- Tell students they are going to be looking at data sets that show monthly measurements of the average global land and ocean temperature over approximately 136 years. They will make a determination about what they think is happening to the global temperature over time.
- Data is contained in two columns. The first column contains date information. The first four digits represent the year and the last two digits represent the month:
188001= Jan 1880
188002 = Feb 1880
188012 = Dec 1880
The second column is the Global Land and Ocean Temperature Anomaly in °C, compared with the average temperature, 13.9°C, from 1901 to 2000.
- Explain to students the concept of anomaly, why scientists often use this instead of actual temperature readings, and how to compute the actual temperature from the anomaly.
- There are several options for importing text data into spreadsheet software. If students will be using the data already in a CSV file, skip to Step 9. Otherwise, students can copy and paste data from the text file into the spreadsheet software. Depending on which software is used, the data may automatically be separated into columns. If it is not, use the Text to Columns (Microsoft Excel) or Split text to columns (Google Sheets) tool to separate the text into separate columns, divided by tabs.
Alternatively, students can use the Import tool to locate the text file. Again, the software may automatically separate the data into columns, but if not, separate the text into columns using the tool(s) mentioned above.
- With the data in an open spreadsheet, create a third column labeled “actual temperature.” Create a formula that will fill the third column with actual temperature data as computed by adding 13.9°C to the corresponding anomaly for each month.
- Google Sheets or Microsoft Excel:
- Type a header for column C. Click in Cell C5 and enter “=13.9+”.
- Then click Cell B5 and click enter or return.
- Click in Cell C5, grab the fill handle (tiny box in the bottom right corner of the cell) and drag to fill data into all the cells, C6 through C1648.
- Google Sheets:
- Highlight all of the data in both columns that you want to graph.
- Click the Insert menu and select Chart.
- In the Chart Editor window, click the Chart types tab. If not already selected, click Use row 4 as headers and Use column A as labels.
- Then select Line chart and click the Insert button.
- Microsoft Excel:
- Click to select a blank cell.
- From the Insert menu, click Chart and select Line. (Alternatively, select Line chart from within the Insert ribbon).
- In the blank chart area that appears, right click and select Choose Data.
- Click in the Chart data range box and select all of the temperature data in Column C, from Cell C5 to Cell C1648.
- Click in the Horizontal (Category) axis labels box and select all of the year data in Column A, from Cell A5 to Cell A1648, and click OK.
- Note: Selecting data and creating a line chart by default will not display the data correctly. If students want to select data and make a chart, they should select the data and choose scatter plot. Data will be displayed correctly and can then be turned into a line chart.
- Google Sheets:
- Right click on the line chart and select Advanced Edit.
- Within the Customization tab, find the Trendline option.
- Select Polynomial and Degree 2 (or higher) and click Update.
- Microsoft Excel:
- Add a nonlinear trendline. There are different ways to add trendlines, depending on which version of Excel is being used. Generally, clicking on the line chart and selecting the Chart Design or Chart Layout tab will provide options to add a trendline directly, or add chart elements, including trendlines.
- Use the Trendline Options feature to select your preferred regression type. Have students play with regression options to select a best-fit polynomial.
- What is the difference between weather and climate?
The difference between weather and climate is a measure of time and area. Weather “describes” the conditions of the atmosphere over a short period of time in a local area. Climate is how the atmosphere “behaves” over relatively long periods of time, regionally or globally.
- How can we separate fact from fiction in science?
Consult reliable sources, such as those at research institutions, especially those involved in data collection, and preferably numerous reliable sources that can corroborate information.
- Compare the class graph with a historical timeline of events in the United States and the world. What associations do you see?
As industrialization rose, so did global temperature averages.
- What steps can you take to reduce your impact on global temperature rise?
Learn how to lower your carbon footprint.
- (High school) How can we learn about global temperatures prior to 1880?
Study isotopic ratios of oxygen in ice cores.
- Assess graphs for accurately placed data points.
- Determine whether students are making progress on their ability to determine how to properly scale data when making a graph.
- Determine whether students are able to indicate trends of increase or decrease on the graph.
- Assess student ability to use spreadsheet software to analyze data.
- Assess student ability to identify trends in graphically represented data.
- Assess student ability to associate human activity with global temperature trends.