Warming to Global Warming: Sunspots and Sea-Surface Temperature
Landstrom, Erich, The Science Teacher
Solar radiation--or radiant energy emitted by the Sun--is the dominant, direct energy input into Earth's atmosphere and climate. In my astronomy class, I assign students (in grades 11 and 12) a problem-based laboratory activity in which they evaluate the causality of changes on the solar surface in regard to climate change and warming in Earth's environment. Students use graphing calculators and real-time data from the internet to research the possible effects of sunspot activity on ocean temperatures in the Atlantic. Sunspots are relatively cool areas of magnetic disturbance on the Sun's surface that appear as dark blotches contrasted against the rest of the photosphere (Figure 1). For this activity, I use the 5E constructivist instructional model--Engage, Explore, Explain, Elaborate, and Evaluate (Bybee 1997)--to analyze a false hypothesis linking sea-surface temperature to the Sun.
To generate interest in the global warming issue, students are engaged with the ideas of British economist William Jevons (1835-1882), who hypothesized that sunspots directly affect economic prosperity. Jevons reasoned that sunspots might have an effect on solar energy, in turn affecting the weather on Earth, which in turn, affects crops. These crop changes would then result in economic changes because agricultural production contributes significantly to the national economy--fluctuations in farm output, prices, and incomes could cause instability in overall business activity. Global warming due to sunspot activity could also lead to drought, which may lead to crop failure, which might depress the economy by causing famine and starvation.
Although Jevons' thinking was incorrect, I deliberately omit alternative explanations. I suggest to students that astronomers could count the number of sunspots as a possible proxy for measuring the magnitude of solar energy output. More sunspots might mean more radiation was being made at the solar interior by fusion--resulting in more magnetic disturbances, or sunspots.
[FIGURE 1 OMITTED]
Continuing with this (flawed) logic, I propose that when the sunspot count--and consequently solar energy--rises, Earth's ocean temperature should also rise. If the hydrosphere covers approximately 70% of Earth with water, then the majority of the surface should respond with a temperature change. Conversely, as the sunspot count falls, so too should the water temperature.
After students are presented with this (faulty) logic, they are asked to provide proof of Jevons' ideas by plotting monthly sunspot numbers versus time over a 16-year period (or 192 months) on a graphing calculator, and, in a second graph, sea-surface temperature versus time over the same period. Students compare the two graphs to determine whether their data analysis identifies a relationship between the Sun and Earth's temperature.
Students explore sunspot data directly on the National Oceanic and Atmospheric Administration (NOAA) website (see "On the web" at the end of the article). Monthly sunspot numbers are prepared by NOAA's Space Weather Prediction Center (SWPC), the nation's official source of space weather alerts and warnings. The SWPC continually monitors and forecasts Earth's space environment; provides accurate, reliable, and useful solar-terrestrial information; conducts and leads research and development programs to understand the environment and to improve services; advises policymakers and planners; plays a leadership role in the space weather community; and fosters a space weather services industry. The recent solar indices (preliminary) of observed monthly mean values provide recent solar indices running from January 1991 to the present. Figure 2 displays the figures from 1991. (Note: An instructor's guide for using graphing calculators to analyze sunspot numbers can be downloaded in PDF format from NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) website [see "On the web"]. …