Little Ice Age Data Analysis

Students receive data about tree ring records, solar activity, and volcanic eruptions during the Little Ice Age (AD 1350–1850). By comparing and contrasting time intervals when tree growth was at a minimum, solar activity was low, and major volcanic eruptions occurred, they draw conclusions about possible natural causes of climate change.

Learning Objectives

  • Students will read and interpret graphs about natural events.
  • Students will communicate their understanding of scientific data to peers.
  • Students will describe climate and changes in climate during the Little Ice Age.

Materials

Preparation

  • Make copies of the Student Pages (Solar Activity, Volcanic Activity, and Tree Growth) for each group. Determine if each group will analyze just one student page or all three to prepare the appropriate number of copies.
  • Use the Putting It All Together page as a guide to create a chart on the board or on chart paper, or plan to have students add their data directly to the Summary Slide (slide 2).
  • Note: Students should have some familiarity with the Little Ice Age and the different types of paleoclimatology data from this time period before beginning this activity.

Directions

  1. Explain to students that they will compile and interpret clues about the causes and effects of the Little Ice Age. The clues that they will use are data about past natural phenomena.
  2. As a class, brainstorm a list of natural events that could cause the Earth's climate to cool and a list of effects that climate cooling might have on Earth. Record the list on the board or somewhere that students have access to.
  3. Arrange the students into groups of three or four.
  4. Provide each group with Student Page 1, 2, or 3. (Or, provide all three pages to each group or each student.)
  5. Give students time to study the graph(s) of solar activity, volcanic activity, and/or tree growth and discuss with each other as they answer the questions on their student page(s). Have a student from each group record group answers.
  6. Project the Summary Slide (slide 2) or direct students to the Putting It All Together page (or chart you have drawn on the board). Explain that they will collectively use the table to summarize the solar, volcano, and tree ring data.
  7. Invite each group to report their conclusions about solar activity, volcanic ash in the atmosphere, and tree growth.
  8. Ask one student from each group to mark the time periods for lowest tree growth, lowest amount of sun spots, and highest amount of volcanic particles in the atmosphere on the Summary Slide (slide 2) or chart by drawing an "x" or a vertical line that covers the time period they think is best represented by their data.
  9. Ask the students if they can see any relationships between the tree ring, solar, and volcanic activity. Review class brainstorms from the introduction in the context of their data interpretation (for example, fewer sunspots correlates with cooling).
  10. Ask students to hypothesize with their group when the coolest part of the Little Ice Age was, according to their data interpretation (slide 3). Share out and discuss group ideas as a whole class.

Background

The Little Ice Age

The Little Ice Age (AD 1350–1850) was a period of particularly harsh climatic conditions around the Northern Hemisphere. A combination of decreased solar activity and numerous large volcanic eruptions cooled the Earth. Cooling caused glaciers to advance and stunted tree growth. Livestock died, harvests failed, and humans suffered from the increased frequency of famine and disease. The Little Ice Age illustrates changes to climate that occur when the Sun is less active and the cooling of Earth is exacerbated by volcanic eruptions. Many other examples of climate change due to natural forces exist, including the Year Without a Summer (1816), which followed the 1815 eruption of Mount Tambora in Indonesia.

Solar and Volcanic Influences on Climate

This is a diagram showing energy from the Sun reaching Earth and the either being absorbed, reflected, or radiated between the surface and the atmosphere and then lost back to space.

Source: NASA. Larger version suitable for class-room use available at Energy pdf - NASA.

Earth's climate is determined by the amount of energy it receives from the Sun, minus the amount of energy that is reflected back into space. This is known as Earth's "energy budget." The climate warms or cools depending on the difference between energy absorbed and energy reflected.

Variations in the amount of solar radiation due to variations in the number of sunspots, affect this balance. Volcanic eruptions produce clouds of dust, ash, and other tiny particles that encourage clouds to form, blocking incoming solar radiation and causing cooling. The combined effects of the solar cycle and volcanic eruptions naturally force changes in the climate. The Little Ice Age occurred at a time when the Sun's activity was at a minimum and volcanoes were very active. No sunspots were seen from 1645 to 1715, and volcanoes in South America and East Asia produced massive eruptions from 1600 through 1700.

Cycles of Solar Activity

The energy output of the Sun, once thought to be constant, varies on an 11-year cycle in response to changes in the solar magnetic fields. Sunspots, areas of high magnetic activity, appear in greater or lesser numbers as the solar magnetic fields change. Cooler than their surroundings, sunspots occur along with heat producing events called faculae and flares. As a result, periods of intense sunspot activity correspond with increased energy from the Sun and warmer periods on Earth. Earth cools when sunspot activity decreases.

This is a drawing of sun spots as recorded by Galileo

Sunspots as recorded by Galileo on June 26, 1613

The astronomer Galileo Galilee observed and recorded sunspots in the early 1600s with the aid of one of the first telescopes. Since then, astronomers have kept a near-complete record of sunspot activity. These records show that the numbers of sunspots increase and decrease approximately every 11 years.

In 1890, astronomer E.W. Maunder reviewed centuries of sunspot data and identified a period (1645–1715) during which few or no sunspots formed. The period, known as the Maunder Minimum, coincided with years of hardship and harsh winter conditions in Europe. Scientists have used other methods to look for increases and decreases in solar activity, including examining the concentration of beryllium-10, an isotope produced in abundance when the magnetic activity of the Sun decreases.

Volcanic Eruptions Cool Earth

Volcanic activity affects the Earth's energy budget. Major volcanic activity produces a layer of ash and gas in the atmosphere that scatters incoming sunlight, therefore causing Earth to cool. Sulfur gas, shot into the atmosphere by an eruption, combines with water vapor in the atmosphere to form a layer of sulfuric acid. This layer of very fine molecules increases the reflectivity of the atmosphere and therefore Earth's albedo.

Albedo describes the ability of a surface to reflect light. Albedo is measured on a scale from zero to one, where zero represents no reflectivity and one represents 100% reflectivity. On average, Earth reflects 31% of the energy it receives from the Sun. However, the Earth’s surface does not reflect energy uniformly. Clouds, ice, and snow reflect up to 90% of the light from the Sun, whereas oceans reflect only about 10%. The eruption of Mount Pinatubo in June of 1991 forced approximately 25 tons of material into the atmosphere, increasing the atmospheric sulfuric acid content by 100 times. Following the Pinatubo eruption, Earth cooled by 0.5 degrees Celsius.

Eventually, precipitation cleanses the atmosphere of the volcanic ash and gas. The layer of sulfuric acid in the atmosphere settles and forms a layer of acid-rich ice at the poles. Polar ice layers preserve the record of ancient volcanic activity, and scientists measure the levels of sulfuric acid in ice cores to reconstruct this record.

Looking for Patterns in Data

The British began the study of climate in the mid-1800s in an effort to predict the monsoon season and plan ocean travel to colonies in the Far East. One scientist, Charles Meldrum, found that monsoons increased as the number of sunspots increased. This study drew attention to the relationship between Earth’s climate and the Sun. Scientists reasoned that the Sun’s energy drove the climate and weather patterns on Earth, especially seasonal storms such as monsoons. A flurry of research activity produced numerous studies that related solar activity to observed phenomena on Earth, including wine production, rainfall, insect population, and more. Discrepancies in the research data pointed out that the 11-year solar cycle explained only some of the changes in climate. Sometimes, when the activity of the Sun increased, the climate did not warm as predicted. At other times, cooling was extreme. Scientists began to look for other contributing factors to the Sun/climate change relationship. In 1960, Hubert Lamb proposed that volcanic activity accounted for the randomness of some climate data. Since then, studies have shown that volcanic activity cools the climate and exacerbates cooling or inhibits warming trends associated with the 11-year solar cycle.

Nature responds to short- and long-term cycles of climate change. Trees react to both punctuated volcanic events and long-term solar activity, which causes variations in the growing season. Other natural processes are influenced by changes in the climate as well. For example, the bloom date for a flowering plant such as the cherry tree varies annually with weather and over many years in response to climate change.

This is a graph showing that an increase in the number of particles in the atmosphere corresponds to the occurrence of volcanic eruptions between 1400 and 1900.

Left, a partial list of major volcanic eruptions from 1400 to the present. Source: Ammann. Right, the amount of particulate matter generated by large volcanic eruptions between 1400 and the present. Source: Ammann.

This activity is included in the CLEAN Climate and Energy Resource Collection, peer-reviewed collection of activities, curricula, videos, and other tools for teaching.

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