Academic journal article The Science Teacher

Measuring C[O.Sub.2]: Students Learn Firtshand How Thawing Permafrost Adds to Global Warming

Academic journal article The Science Teacher

Measuring C[O.Sub.2]: Students Learn Firtshand How Thawing Permafrost Adds to Global Warming

Article excerpt

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In 2016, global air and sea surface temperatures reached their highest levels for the January-through-June period since recordkeeping began in the 1800s. The Arctic is warming about twice as quickly as other regions on Earth due to human production of heat-trapping gases, such as carbon dioxide and methane (NRC 2015). Thus, the Arctic is a bellwether for climate change effects, and rising temperatures are already altering natural processes in the region, which will result in global feedbacks (Huebert 2012).

For example, warming is causing loss of sea and land ice, thawing permafrost soils, and shifting carbon cycling and ecosystems. These changes will result in global sea-level rise, shifts in ocean circulation and weather patterns across Earth, and changes in global climate (NRC 2015).

The thawing of permafrost soils may be the change felt most directly, because it will intensify the greenhouse effect, substantially affecting Earth's climate.

Permafrost is soil or rock that remains constantly at or below 0[degrees]C for at least two years (National Geographic 2007). Permafrost covers 25% of the northern hemisphere land surface--approximately 23 million [km.sup.2]-- and can be more than a kilometer deep (NSIDC 2016). Permafrost plays an important role in the planet's carbon cycle and global climate because it holds up to 1,700 billion tons of carbon (1700 Pg) (United Nations Environment Programme 2013). As a major carbon sink, permafrost sequesters carbon dioxide from the atmosphere in the form of organic matter for thousands of years. The sequestered carbon comes from plants that live in the thin layer of topsoil. In summer, this topsoil thaws, allowing plant growth and decomposition to occur. The plants take in C[O.sub.2] from the atmosphere and, through photosynthesis, turn it into organic carbon (i.e., organic matter). When plants die, microorganisms decompose the organic matter, releasing some of the carbon back to the atmosphere as carbon dioxide and methane, while some remains in the soil as organic matter. This annual decomposition occurs only during the short northern summer, so only a small amount of organic matter is returned to the atmosphere as greenhouse gases. Over time, the carbon stored in cold soils builds up layer by layer, as once-living plant matter becomes frozen organic matter. This results in the vast store of carbon now locked in permafrost soils across the Arctic.

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As permafrost soils warm and thaw, increasing amounts of organic matter are available for decomposition. Organic matter also is dissolved in groundwater that flows into lakes and streams (Cory et al. 2014). Thus, warming increases the rate at which permafrost carbon is converted to carbon dioxide and methane, promoting more global warming. In this positive feedback process, a warmer global climate leads to thawing permafrost, which in turn leads to increasing greenhouse gas production and an even warmer climate. The ongoing thawing of permafrost soils, which hold twice as much carbon as the atmosphere itself (Tarnocai et al. 2009), could allow tremendous stores of organic carbon to be converted into C[O.sub.2] in a relatively short time, accelerating global warming.

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Given the increasing pressure on countries to limit their C[O.sub.2] emissions, consider that to stabilize the atmosphere at 450 ppm C[O.sub.2], corresponding to a ~3[degrees]C increase above current global temperatures, the world can emit a maximum of another 45 billion tons (Gt) of carbon. This amount could easily come from the carbon stored in permafrost as organic matter, suggesting that other C[O.sub.2] emissions will have to be severely constrained.

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This article presents simple tools and concepts to engage students in inquiry-based learning about the carbon cycle, thawing permafrost, and climate change. …

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