AP Environmental Science Unit 9 study games — Global Change.

A student is asked: 'As Arctic permafrost melts due to rising temperatures, large amounts of methane are released. Explain how this represents a positive feedback loop and predict its effect on future warming.'

Melting permafrost releases stored methane (CH4), a potent greenhouse gas, which increases the greenhouse effect and raises temperatures further. Higher temperatures then melt more permafrost, releasing even more methane — each step amplifies the next, which is the defining characteristic of a positive feedback loop. The net effect is accelerated warming beyond what the initial CO2 emissions alone would have caused.

A graph shows atmospheric CO2 concentration (ppm) and global average temperature (°C) over the last 800,000 years from ice core data. The question asks: 'Describe the relationship shown and explain the mechanism linking CO2 to temperature.'

The graph shows a strong positive correlation — when CO2 rises, temperature rises, and both follow similar cyclical patterns tied to glacial/interglacial periods. The mechanism is that higher CO2 concentrations increase absorption of outgoing infrared radiation, trapping more heat in the lower atmosphere and raising surface temperatures. Students should note this is correlation supported by a known physical mechanism, not mere coincidence.

An experiment exposes oyster larvae to seawater at pH 8.1 (current), 7.9, and 7.7. Shell formation rate decreases significantly at each lower pH. The question asks: 'Identify the chemical cause of reduced shell formation and predict one ecosystem-level consequence if pH reaches 7.7 in coastal waters.'

Lower pH means higher H⁺ ion concentration, which reacts with carbonate ions (CO3²⁻) to form bicarbonate (HCO3⁻), reducing the carbonate available for shell formation (CaCO3). Oyster larvae cannot form protective shells, increasing mortality rates. At the ecosystem level, the collapse of oyster populations would remove a major filter feeder, reducing water quality and disrupting the food web that depends on bivalves as prey.

Zebra mussels were introduced to the Great Lakes via ballast water in the 1980s. They filter phytoplankton at extremely high rates. The question asks: 'Explain two ways zebra mussels harm the native Great Lakes ecosystem and evaluate one management strategy.'

First, by filtering massive quantities of phytoplankton, zebra mussels reduce food availability for native zooplankton and larval fish, collapsing lower trophic levels. Second, their dense colonies physically smother native unionid mussels and clog water intake infrastructure. A management strategy such as chemical molluscicide (potassium chloride) can reduce local populations in enclosed areas, but is impractical at the scale of the Great Lakes and risks non-target species mortality — making prevention and early detection far more cost-effective than reactive control.