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Unit 9 · Global Change Unit Hub Flashcards Cheat Sheet Essentials Visual Review MC Practice FRQ Practice

AP Environmental Science Unit 9 Visual Review

A 10-slide visual walkthrough of every Topic 9.1-9.10 concept — ozone depletion, the greenhouse effect, ocean warming and acidification, invasive and endangered species, and human impacts on biodiversity — built right into the page.

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TOPIC 9.1 Stratospheric Ozone Depletion stratospheric ozone (O₃) layer CFC UV breaks off Cl atom Cl O₃ Cl destroys O₃, is regenerated — repeats 1000s of times Why the ozone layer matters Stratospheric ozone absorbs most incoming UV radiation, shielding life below from radiation damage — skin cancer, cataracts, and crop damage all increase as this layer thins. One chlorine atom, thousands of hits CFCs (once common in refrigerants and aerosols) release chlorine when broken down by UV light. Each chlorine atom acts as a catalyst, destroying thousands of O3 molecules. This ozone layer protects us from UV; ground-level ozone (7.2) is a harmful pollutant — don't mix up the two. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.2 Reducing Ozone Depletion ozone-depleting emissions 1987 (Montreal Protocol) → today treaty signed The Montreal Protocol (1987) A global treaty that phased out CFCs and other ozone-depleting chemicals, replacing them with safer alternatives in refrigeration and aerosols. The exam's favorite success story Nearly every country ratified it, and the ozone layer is now measurably recovering — proof that global cooperation CAN reverse an atmospheric crisis when the cause is narrow. Compare this to climate change (9.3-9.5): a single, well-defined cause made ozone recovery far easier to negotiate. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.3 The Greenhouse Effect sunlight (visible) in Earth's surface infrared (heat) out greenhouse gas layer (traps IR) A natural, necessary process Sunlight passes through the atmosphere and warms Earth's surface, which re-radiates that energy as infrared (heat). Without ANY greenhouse effect, Earth would be far too cold for life. The problem is the ENHANCED effect Greenhouse gases (CO2, methane, water vapor) absorb and re-emit that outgoing infrared radiation back toward the surface. MORE of these gases traps more heat — warming the planet. The mechanism is about infrared, not visible light — sunlight passes through greenhouse gases easily; outgoing heat doesn't. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.4 Increases in Greenhouse Gases Fossil fuel combustion The single largest source of CO2 — power plants, cars, industry (Unit 6). Agriculture Livestock (methane from digestion) and fertilizer (nitrous oxide, N2O). Deforestation Removes a carbon SINK and releases stored carbon — a double hit (recall 1.4). Two gases, two different strengths CO2 is by far the most ABUNDANT greenhouse gas, so it drives the most total warming. Methane (CH4) is far less abundant but traps roughly 25-80x more heat per molecule (depending on timeframe) — so livestock and landfill methane punch well above their weight despite the smaller quantity released. Ounce for ounce methane is far more potent than CO2, but it also breaks down faster — both facts matter for policy. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.5 Global Climate Change Sea level rise Thermal expansion + melting ice sheets threaten coastal cities. Extreme weather More intense storms, droughts, and heat waves. Shifting ranges Species migrate poleward or to higher elevation as their climate niche moves. Climate vs. weather A single cold day doesn't disprove warming — climate describes long-term AVERAGE conditions over decades, while weather is what happens day to day. Climate change also increases VARIABILITY, which is why extreme weather of all kinds becomes more common, not just heat. Topics 9.6 and 9.7 zoom into two specific consequences of this warming that deserve their own deep dive — the ocean. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.6 Ocean Warming healthy coral algae symbionts give color warming bleached coral The ocean absorbs most excess heat Over 90% of the extra heat trapped by enhanced greenhouse gases goes into the ocean, not the atmosphere — buffering air temperatures but steadily warming the sea. Coral bleaching Heat stress causes coral to expel the symbiotic algae living in their tissue — the same algae that give coral its color AND much of its food, via photosynthesis. Bleached coral isn't dead yet, but it's starving — if warm water persists, the reef collapses. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.7 Ocean Acidification CO₂ + H₂O carbonic acid pH ↓ shell (CaCO₃) acid dissolves shell A separate mechanism from warming The ocean absorbs roughly a quarter of human CO2 emissions directly. Dissolved CO2 reacts with water to form carbonic acid, lowering ocean pH — this is CHEMISTRY, not heat. Shell- and skeleton-builders at risk Lower pH makes it harder for organisms to build calcium carbonate shells and skeletons — threatening corals, oysters, and the tiny plankton that anchor the entire marine food web. Same CO2, two ocean crises: warming (physics — heat absorption) and acidification (chemistry — CO2 dissolving) act independently. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.8 Invasive Species native established niche, natural predators introduced invasive no natural predators, outcompetes natives Why they take over Introduced species (accidentally or deliberately) often arrive without the predators, parasites, or diseases that kept their population in check back home. Real-world examples Zebra mussels clog waterways and outcompete native mussels; Burmese pythons have decimated small mammal populations in the Everglades — both reshape entire food webs. Prevention (inspecting cargo, ballast water rules) is far cheaper than eradication once a species is established. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.9 Endangered Species population size time → threatened critically endangered Main drivers Habitat loss (Unit 5/8) is the single biggest cause worldwide. Overharvesting (overfishing, poaching) and invasive species (9.8) add further pressure to already shrinking populations. Small populations compound the risk Once numbers fall low enough, reduced genetic diversity (2.1) and difficulty finding mates can accelerate decline even if the original threat is later removed. The IUCN Red List formalizes these risk categories — from Least Concern through Endangered to Extinct. The Review Hub · AP Environmental Science Unit 9 TOPIC 9.10 Human Impacts on Biodiversity BIODIVERSITY LOSS habitat loss pollution climate change invasive species Threats compound, not isolate Rarely does one mechanism act alone. A species facing habitat fragmentation is also less able to shift its range as climate change moves its viable habitat — the threats interact. The course's central throughline This is APES in one diagram: land use (Unit 5), pollution (Units 7-8), and global change (9.1-9.9) all converge here — on the biodiversity introduced all the way back in Unit 2. This final topic is the whole course's synthesis question — every unit you've studied feeds into this one outcome. The Review Hub · AP Environmental Science Unit 9
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This covers every one of Unit 9's 10 CED topics, from stratospheric ozone depletion through human impacts on biodiversity.