Graphing Global Temperature Trends

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.

• 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.

• 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.