Unit 9: Global Change
AP Environmental Science: 51 practice questions with detailed explanations.
Unit Study Guide
Executive Summary
Unit 9 tackles planetary-scale change: ozone depletion, climate change, ocean acidification, and the biodiversity crisis — plus the solutions.
Ozone depletion
CFCs released chlorine that catalytically destroyed stratospheric ozone, opening the seasonal Antarctic hole. The Montreal Protocol (1987) phased out CFCs; the layer is slowly recovering. Ozone absorbs UVB — depletion raises skin cancer and cataract risk.
Climate change
Greenhouse gases (CO₂ from fossil fuels — about three-quarters of warming; methane from agriculture and landfills; nitrous oxide; water vapor as a feedback) trap infrared, raising global temperature. Evidence: rising CO₂, warming, melting ice, rising seas, shifting species. Without GHGs Earth would average about −18 °C instead of 15 °C.
Ocean impacts
Oceans absorb heat (thermal expansion, coral bleaching) and CO₂, which forms carbonic acid and lowers pH — ocean acidification — dissolving carbonate shells. Warming also intensifies storms and shifts currents.
Biodiversity crisis
Habitat loss, invasive species, pollution, overharvesting, and climate change drive a sixth mass extinction. Invasive species outcompete natives without their natural enemies. Conservation strategies: protected areas, corridors, captive breeding, and habitat restoration.
Sustainability
Mitigation (cutting emissions: renewables, efficiency) and adaptation (sea walls, drought-tolerant crops) are both needed. Global treaties (Montreal, Kyoto, Paris) coordinate action; individual footprints matter but systemic change dominates.
Exam traps
Ozone depletion and climate change are separate problems with separate treaties — don't merge them. Ocean acidification is CO₂-driven, distinct from warming. Coral bleaching is heat stress, not acidification. Invasive species succeed because of enemy release, not superior genetics.