At the global level, strong evidence suggests that observed changes in Earth's climate are largely due to human activities (IPCC 2007). At the regional level, the evidence for human-dominated change is sometimes less clear. Scientists have a particularly difficult time explaining warming trends in Antarctica--a region with a relatively short history of scientific observation and a highly variable climate (Clarke et al. 2007). Regardless of the mechanism of warming, however, climate change is having a dramatic impact on Antarctic ecosystems. In this article, we describe a standards-based, directed inquiry we have used in 10th-grade biology classes to highlight the ecosystem-level changes observed on the western Antarctic Peninsula. This activity stresses the importance of evidence in scientific explanations and demonstrates the cooperative nature of science.
Warming climate, waning sea ice
Air temperature data indicate that the western Antarctic Peninsula has warmed by about 3[degrees]C in the last century (Clarke et al. 2007). Although this relatively short-term record is only from a few research stations, other indirect lines of evidence confirm the trend. The most striking of these proxies is a shift in penguin communities. Adelie penguins, which are dependent on sea ice for their survival, are rapidly declining on the Antarctic Peninsula despite a 600-year colonization history. In contrast, chinstrap penguins, which prefer open water, are increasing dramatically. (Note: See "Chinstrap and Adelie penguins," p. 58, for additional information on the penguins.) These shifts in penguin populations appear to be the result of a decrease in the amount, timing, and duration of sea ice (Figure 1; Smith, Fraser, and Stammerjohn 2003).
Why is sea ice so important to Adelie penguins? First, sea ice is a feeding platform for Adelies. Krill, the primary prey of Adelies on the Peninsula, feed on microorganisms growing on the underside of the ice (Atkinson et al. 2004). For Adelie penguins, which are relatively slow swimmers, it is easier to find food under the ice than in large stretches of open water (Ainley 2002). Second, sea ice helps control the local climate. Ice keeps the Peninsula cool by reflecting solar radiation back to space. As air temperatures increase and sea ice melts, open water converts radiation into heat and amplifies the upward trend in local air temperatures (Figure 2; Wadhams 2000). Third, ice acts as a giant cap on the ocean, limiting evaporation. As sea ice declines, cloud condensation nuclei and moisture are released into the atmosphere, leading to more snow. This extra snow often does not melt until Adelies have already started nesting; the resulting melt water can kill their eggs (Fraser and Patterson 1997).
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For our directed inquiry, we use the jigsaw technique, which requires every student within a group to be an active and equal participant for the rest of the group to succeed (Colburn 2003). To begin, students are organized into "Home Groups" composed of five different specialists. (Note: See "Procedure" in the next section for specific instructions on how each student assumes the identity of a different specialist.) Specialists from each Home Group then reorganize into "Specialist Groups" that contain only one type of scientist (e.g., Group 1 could include all of the Ornithologists and Group 2 all of the Oceanographers). Each Specialist Group receives a piece of the flowchart in Figure 1 (p. 57), in the form of a data table. With only a few facts to guide them, the Specialist Groups create graphs from the data tables, brainstorm explanations for patterns in their data, and report results back to their Home Groups. Finally, Home Groups use the expertise of each specialist to reconstruct the entire flowchart (Figure 1, p. 57).
Before starting this activity, students should have at least a rudimentary knowledge of Antarctica. …