Global Change
Complete review of all 10 topics — ozone depletion, greenhouse effect, climate change, ocean impacts, invasive and endangered species, and biodiversity conservation. Highest exam weight: 15–20%.
Stratospheric Ozone Depletion
The ozone layer in the stratosphere (~15-35 km altitude) absorbs ~97-99% of the sun's harmful ultraviolet (UV-B) radiation. Chlorofluorocarbons (CFCs), once used as refrigerants, aerosol propellants, and foam-blowing agents, release chlorine atoms in the stratosphere that catalytically destroy ozone molecules.
| Concept | Details |
|---|---|
| Ozone Formation | O₂ + UV → 2O; O + O₂ → O₃ (naturally cycles in stratosphere) |
| CFC Destruction | UV breaks CFC → free Cl; Cl + O₃ → ClO + O₂; ClO + O → Cl + O₂ (Cl is regenerated — catalytic) |
| Amplification | One chlorine atom destroys ~100,000 ozone molecules before being deactivated |
| Ozone Hole | Seasonal thinning over Antarctica (worst in September-October); polar stratospheric clouds accelerate destruction |
| Other ODS | Halons (fire extinguishers), methyl bromide (fumigant), HCFCs (transitional replacements) |
Increased skin cancer (melanoma), cataracts, suppressed immune system. A 1% decrease in ozone = ~2% increase in UV-B reaching Earth's surface.
Kills phytoplankton (base of marine food web), damages amphibian eggs, reduces crop yields, degrades plastics and materials.
Stratospheric ozone is "good ozone" (protective shield). Ground-level ozone is "bad ozone" (pollutant, smog). Same molecule, different location, opposite effects.
Don't confuse ozone depletion (stratospheric, caused by CFCs, UV radiation problem) with the greenhouse effect (tropospheric, caused by CO₂/CH₄, heat trapping problem). They are separate issues — though CFCs happen to be both ozone-depleting AND greenhouse gases.
Chlorofluorocarbons (CFCs) deplete the ozone layer because
- (A) they react with oxygen to form carbon dioxide
- (B) UV radiation releases chlorine atoms that catalytically destroy ozone
- (C) they absorb UV radiation that would normally create ozone
- (D) they react with nitrogen to form nitrous oxide
Reducing Ozone Depletion
The Montreal Protocol (1987) is widely regarded as the most successful international environmental agreement in history. It phased out production of CFCs and other ozone-depleting substances (ODS), with 197 countries ratifying it — universal participation.
CFC production has dropped by over 99% since the Protocol. The ozone layer is recovering and is expected to return to 1980 levels by approximately 2066 over Antarctica and 2045 globally. Transitional substitutes included HCFCs (less ozone-damaging but still harmful), now being replaced by HFCs (no ozone damage but potent greenhouse gases) and newer alternatives.
The Montreal Protocol is the AP exam's go-to example of a successful international environmental treaty. Contrast it with the Kyoto Protocol and Paris Agreement (climate change — less successful so far). Key success factors: clear science, available substitutes, industry cooperation, financial aid to developing nations (Multilateral Fund).
The Kigali Amendment (2016) to the Montreal Protocol now phases down HFCs (greenhouse gases used as CFC replacements). This single amendment could prevent up to 0.5°C of global warming by 2100 — connecting the ozone treaty to climate change mitigation.
The Montreal Protocol has been considered the most successful international environmental treaty primarily because it
- (A) eliminated all greenhouse gas emissions from developed countries
- (B) reduced global temperatures by 2°C since its ratification
- (C) achieved near-universal participation and measurable ozone layer recovery
- (D) banned all uses of chlorine-containing chemicals worldwide
The Greenhouse Effect
The greenhouse effect is a natural process essential for life: greenhouse gases in the atmosphere absorb and re-radiate infrared (longwave) radiation emitted by Earth's surface, warming the lower atmosphere. Without it, Earth's average temperature would be ~-18°C instead of +15°C. The problem is the enhanced (anthropogenic) greenhouse effect — human activities increasing GHG concentrations beyond natural levels.
| Greenhouse Gas | Formula | GWP (100-yr) | Major Anthropogenic Sources | Atmospheric Lifetime |
|---|---|---|---|---|
| Carbon Dioxide | CO₂ | 1 (reference) | Fossil fuel combustion, deforestation, cement production | 300-1,000 years |
| Methane | CH₄ | 28-36 | Livestock (enteric fermentation), rice paddies, landfills, natural gas leaks | ~12 years |
| Nitrous Oxide | N₂O | 265-298 | Agricultural fertilizers (nitrification/denitrification), combustion | ~121 years |
| CFCs/HFCs | Various | 1,000-23,000 | Refrigerants, aerosols, foam blowing | Variable (decades-centuries) |
| Water Vapor | H₂O | N/A | Not directly controlled; acts as feedback (warming → more evaporation → more warming) | ~10 days |
GWP (Global Warming Potential) compares how much heat a greenhouse gas traps relative to CO₂ over a specific period (usually 100 years). Methane has a GWP of 28-36, meaning 1 ton of CH₄ traps 28-36x more heat than 1 ton of CO₂. However, CO₂ is the most important GHG because its total emissions are vastly higher and it persists for centuries.
Although methane has a higher global warming potential per molecule than carbon dioxide, CO₂ is considered the most important anthropogenic greenhouse gas because
- (A) methane does not absorb infrared radiation
- (B) CO₂ is emitted in much larger quantities and persists for centuries
- (C) CO₂ has a higher global warming potential than methane
- (D) methane is only produced by natural sources
❌ Saying the greenhouse effect is bad: The natural greenhouse effect is essential — without it Earth would be -18°C. The ENHANCED (anthropogenic) greenhouse effect from excess GHGs is the problem.
❌ Claiming CH₄ is the most important GHG: Methane has higher per-molecule warming potential (GWP 28-36), but CO₂ is the most important anthropogenic GHG because it is emitted in far greater quantities and persists for centuries.
❌ Forgetting water vapor: H₂O vapor is the most abundant greenhouse gas, but humans don't directly control it. It acts as a positive feedback — warming → more evaporation → more H₂O vapor → more warming.
Increases in the Greenhouse Effect
Human activities have increased atmospheric CO₂ from ~280 ppm (pre-industrial) to over 420 ppm — a 50% increase, higher than at any point in at least 800,000 years (ice core data). This enhanced greenhouse effect is the primary driver of modern climate change.
Burning coal, oil, and natural gas releases ~36 billion tons of CO₂/year — the largest anthropogenic source (~75% of total). Transportation, electricity, and industry are the main sectors.
Clearing forests releases stored carbon and removes a carbon sink. Accounts for ~10% of global CO₂ emissions. Tropical deforestation (Amazon, Southeast Asia) is the most impactful.
Livestock produce methane (enteric fermentation); rice paddies release methane (anaerobic decomposition); fertilizers produce N₂O. Agriculture accounts for ~10-12% of global GHG emissions.
Ice-albedo feedback: warming melts ice → darker surface → absorbs more heat → more warming. Permafrost thaw: releases stored CH₄ and CO₂ → more warming → more thaw. Water vapor feedback: warming → more evaporation → more GHG → more warming.
Arctic permafrost contains an estimated 1,500 billion tons of carbon (twice the current atmospheric CO₂). As global temperatures rise, thawing permafrost releases methane and CO₂, creating a positive feedback loop that could accelerate warming beyond human control. This is considered one of the most dangerous climate tipping points.
The ice-albedo feedback loop accelerates global warming because
- (A) melting ice releases trapped greenhouse gases
- (B) ice reflects infrared radiation back to Earth's surface
- (C) loss of reflective ice exposes darker surfaces that absorb more solar radiation
- (D) ice formation requires heat energy from the atmosphere
Global Climate Change
Global average temperature has risen ~1.1°C since pre-industrial times, and is on track for 1.5°C by the early 2030s. The IPCC (Intergovernmental Panel on Climate Change) states with >95% confidence that human activities are the dominant cause. Effects are already observable and will intensify.
| Category | Observed and Projected Effects |
|---|---|
| Temperature | More frequent and intense heat waves; Arctic warming 2-3x faster than global average (Arctic amplification) |
| Precipitation | Wet regions getting wetter, dry regions drier; more intense storms; shifts in monsoon patterns |
| Sea Level | Rising ~3.6 mm/year (thermal expansion + ice melt); threatens coastal cities, islands, deltas; ~1 billion people at risk |
| Ecosystems | Species range shifts poleward/upslope; coral bleaching; phenology mismatches (spring arriving earlier); increased wildfires |
| Human Systems | Agricultural disruption, water scarcity, climate refugees, disease range expansion (mosquito-borne), infrastructure damage |
Reducing GHG emissions: transition to renewables, energy efficiency, carbon capture, reforestation, methane reduction. Goal: limit warming to 1.5-2°C (Paris Agreement, 2015).
Adjusting to inevitable changes: sea walls, drought-resistant crops, early warning systems, managed retreat from coasts, improved water infrastructure.
196 parties committed to limit warming to well below 2°C, pursue 1.5°C. Each country sets its own NDCs (Nationally Determined Contributions). Not legally binding.
This is the most heavily tested topic in Unit 9. Be able to: distinguish mitigation (reduce causes) from adaptation (adjust to effects), explain positive feedback loops, interpret temperature/CO₂ graphs, compare international agreements (Montreal Protocol vs. Paris Agreement), and discuss environmental justice (developing nations are most vulnerable but least responsible).
A country building higher sea walls to protect coastal communities from rising ocean levels is an example of
- (A) mitigation of climate change
- (B) adaptation to climate change
- (C) geoengineering
- (D) carbon sequestration
❌ Confusing mitigation with adaptation: Mitigation = reducing the CAUSE (cutting GHG emissions, switching to renewables). Adaptation = adjusting to the EFFECTS (sea walls, drought-resistant crops). Building solar panels is mitigation; building sea walls is adaptation.
❌ Sea level rise is ONLY from melting ice: Wrong — thermal expansion of warming ocean water accounts for ~40% of current sea level rise. Both thermal expansion AND ice melt contribute.
❌ Mixing up Montreal Protocol and Paris Agreement: Montreal Protocol (1987) = ozone depletion, nearly universal success, legally binding. Paris Agreement (2015) = climate change, voluntary NDCs, not legally binding. Different problems, different treaties, different outcomes.
Scientists studying climate change have documented that atmospheric CO₂ levels have risen from 280 ppm (pre-industrial) to over 420 ppm today.
(a) Explain the mechanism by which increased CO₂ concentrations enhance the greenhouse effect and lead to global warming. (3 points)
(b) Describe TWO positive feedback loops that could accelerate warming beyond what CO₂ alone would cause. For each, explain why it is a positive (not negative) feedback. (4 points)
(c) A country proposes two climate policies: (1) building a network of offshore wind farms and (2) developing drought-resistant crop varieties. Classify each as mitigation or adaptation and justify your classification. (2 points)
(b) Two Positive Feedback Loops (4 pts — 2 each): (1) Ice-albedo feedback: warming melts highly reflective ice and snow (high albedo), exposing darker ocean or land surfaces that absorb more solar energy, which causes further warming and further ice melt. It is positive because the output (warming) amplifies the input (warming). (2) Permafrost thaw feedback: rising temperatures thaw Arctic permafrost, releasing stored methane (CH₄) and CO₂ from decomposing organic matter. These additional GHGs trap more heat, causing more warming, which thaws more permafrost. It is positive because each cycle amplifies the original warming signal rather than counteracting it.
(c) Policy Classification (2 pts): (1) Offshore wind farms = MITIGATION — they address the cause of climate change by replacing fossil fuel electricity generation with zero-emission renewable energy, thereby reducing CO₂ emissions. (2) Drought-resistant crops = ADAPTATION — they do not reduce GHG emissions but help human systems adjust to the effects of climate change (altered precipitation patterns, increased droughts) that are already occurring or expected.
Ocean Warming
The ocean absorbs over 90% of the excess heat trapped by greenhouse gases. This ocean warming has profound consequences for marine ecosystems, weather patterns, and sea level. The top 700 meters of the ocean has warmed significantly since the 1970s.
When water temperatures rise just 1-2°C above the normal summer maximum, corals expel their symbiotic algae (zooxanthellae), turning white. Prolonged bleaching leads to coral death. Back-to-back bleaching events give reefs no recovery time.
Thermal expansion of warming water accounts for ~40% of current sea level rise. Combined with ice melt, seas are rising ~3.6 mm/year and accelerating. Threatens coastal cities, island nations, and deltas.
Marine species are shifting poleward at ~70 km/decade — faster than terrestrial species. This disrupts fisheries, alters food webs, and brings tropical species (and diseases) to temperate waters.
Warmer ocean surface temperatures provide more energy for hurricanes and typhoons, making them more intense (higher wind speeds, more rainfall). The number of Category 4-5 hurricanes has increased.
Coral reefs support ~25% of all marine species despite covering less than 1% of the ocean floor. The Great Barrier Reef has experienced mass bleaching in 2016, 2017, 2020, 2022, and 2024. Scientists project that 70-90% of reefs will disappear at 1.5°C warming, and virtually all at 2°C.
Coral bleaching occurs primarily when
- (A) ocean pH drops below 7.8
- (B) water temperatures rise above the coral's thermal tolerance
- (C) excess nutrients cause algal blooms on reef surfaces
- (D) UV radiation penetrates deeper due to ozone depletion
Ocean Acidification
The ocean absorbs about 25-30% of human-emitted CO₂, which reacts with seawater to form carbonic acid: CO₂ + H₂O → H₂CO₃. This process, called ocean acidification, has lowered ocean pH by ~0.1 units since the industrial revolution — a 30% increase in acidity (pH is logarithmic).
Lower pH reduces the availability of carbonate ions (CO₃²⁻) that marine organisms need to build calcium carbonate shells and skeletons. Affected organisms include corals, oysters, clams, sea urchins, and pteropods (sea butterflies — critical food source for salmon). As waters become more corrosive, existing shells can dissolve.
Ocean acidification is sometimes called "the other CO₂ problem" (alongside climate change). It is a direct chemical consequence of CO₂ absorption — it would occur even without temperature change. The only solution is reducing CO₂ emissions; there is no technological fix for a global ocean.
Students often say the ocean is "becoming acidic." Technically, ocean water is still basic (pH ~8.1, down from ~8.2). "Acidification" means becoming more acidic (lower pH), not that it has crossed pH 7 into the acidic range. Also remember: a 0.1 pH decrease = 30% more H⁺ ions because the scale is logarithmic.
Ocean acidification most directly threatens marine organisms that
- (A) rely on dissolved oxygen for respiration
- (B) are adapted to warm tropical waters
- (C) build shells or skeletons from calcium carbonate
- (D) depend on photosynthesis for energy production
Invasive Species
Invasive species are non-native organisms that, when introduced to a new environment, spread rapidly and cause ecological or economic harm. They thrive because they lack natural predators, diseases, and competitors in their new range. Invasive species are the #2 cause of biodiversity loss worldwide (after habitat destruction).
| Invasive Species | Origin → Introduced To | Impact |
|---|---|---|
| Asian Carp | China → US Great Lakes region | Outcompete native fish for food; threaten $7 billion Great Lakes fishing industry |
| Zebra/Quagga Mussels | Black Sea → US Great Lakes | Clog water intake pipes; filter-feed, reducing plankton for native species; $1 billion/year in damage |
| Kudzu | Japan → Southeastern US | Grows up to 1 foot/day; smothers native vegetation and trees; "the vine that ate the South" |
| Brown Tree Snake | Australia → Guam | Eliminated 10 of 12 native forest bird species; power outages from climbing lines |
| Burmese Python | Southeast Asia → Florida Everglades | Decimated native mammal populations (raccoons -99%, opossums -99%, rabbits -100% in survey areas) |
Invasive species arrive via: ballast water (ships take in water with organisms in one port and release in another), intentional introduction (kudzu for erosion control, cane toads for pest control), pet trade escapes (Burmese pythons), contaminated goods, and canal construction (Suez, Panama connecting separated ecosystems).
Invasive species often outcompete native species in a new environment primarily because they
- (A) are genetically superior to native species
- (B) have higher metabolic rates than native species
- (C) lack natural predators and diseases that control their populations
- (D) are better adapted to the local climate
❌ Invasive species succeed because they are "stronger": They succeed because they LACK natural predators, diseases, and competitors in their new environment — not because of inherent superiority. In their native range, they are kept in check.
❌ All non-native species are invasive: A species is only "invasive" if it causes ecological or economic harm. Many non-native species coexist without significant negative impact. The term specifically refers to those that spread aggressively and displace natives.
Endangered Species
An endangered species is one at risk of extinction throughout all or a significant portion of its range. A threatened species is likely to become endangered in the foreseeable future. Current extinction rates are estimated at 100-1,000x the natural background rate — scientists call this the Sixth Mass Extinction.
US federal law prohibiting "take" (harm, harass, pursue, capture) of listed species. Protects critical habitat. Has prevented extinction of bald eagle, gray wolf, American alligator, and others. ~1,700 US species currently listed.
Convention on International Trade in Endangered Species (1975). Regulates/bans international trade in ~38,000 species of plants and animals. Three appendices based on threat level. Combats wildlife trafficking.
Global inventory that classifies species: Least Concern → Near Threatened → Vulnerable → Endangered → Critically Endangered → Extinct in the Wild → Extinct. Over 42,000 species currently threatened with extinction.
In-situ (in habitat): protected areas, wildlife corridors, habitat restoration. Ex-situ (out of habitat): zoos, seed banks, captive breeding. In-situ is preferred; ex-situ is a last resort.
Know the difference between ESA (US domestic law, prohibits "take" of listed species), CITES (international treaty, regulates trade), and IUCN Red List (scientific classification, not legally binding). Also know: lacey Act (prohibits trade in illegally taken wildlife) and Marine Mammal Protection Act.
The primary purpose of CITES (Convention on International Trade in Endangered Species) is to
- (A) establish protected habitat areas for endangered species
- (B) fund captive breeding programs for critically endangered species
- (C) regulate international trade in wild plants and animals to prevent overexploitation
- (D) set pollution limits to protect aquatic species
Human Impacts on Biodiversity
The major threats to biodiversity are summarized by the acronym HIPPCO: Habitat loss, Invasive species, Population growth, Pollution, Climate change, and Overexploitation. Habitat loss is the #1 cause of species decline, driven primarily by agriculture, urbanization, and deforestation.
| Threat (HIPPCO) | Examples | Relative Impact |
|---|---|---|
| Habitat Loss | Deforestation, wetland drainage, urbanization, dam construction | #1 cause — affects ~85% of threatened species |
| Invasive Species | Brown tree snake, zebra mussels, kudzu, cheatgrass | #2 cause — especially devastating on islands |
| Population Growth | More humans → more resource demand → more habitat conversion | Root driver of all other threats |
| Pollution | Pesticides, plastics, oil spills, nutrient runoff, light/noise | Reduces habitat quality even where habitat remains |
| Climate Change | Shifting ranges, coral bleaching, phenology mismatches, sea level rise | Rapidly growing threat — will overtake others by mid-century |
| Overexploitation | Overfishing, poaching (elephants, rhinos), bushmeat trade, shark finning | Direct population reduction; especially affects large, slow-reproducing species |
Breaking continuous habitat into isolated patches. Reduces gene flow, increases edge effects, makes populations more vulnerable to local extinction. Wildlife corridors can reconnect fragments.
Regions with high endemism (species found nowhere else) and severe habitat loss. 36 hotspots cover 2.5% of Earth's land but contain ~50% of all plant species and ~43% of vertebrate species. Prioritized for conservation.
Biodiversity loss threatens: pollination (75% of food crops depend on pollinators), water purification, carbon storage, flood control, disease regulation, and genetic resources for medicine and agriculture.
HIPPCO is the framework for understanding biodiversity threats. For the AP exam, know that habitat loss is #1, invasive species are #2, and climate change is the fastest-growing threat. Also understand that these threats are interconnected — climate change drives range shifts that create new invasive species problems, and habitat loss makes species less resilient to climate change.
Which factor is currently the greatest cause of species extinction worldwide?
- (A) Habitat loss and fragmentation
- (B) Climate change
- (C) Overexploitation and poaching
- (D) Pollution from industrial chemicals
❌ Climate change is the #1 cause of biodiversity loss: Currently, HABITAT LOSS is #1 (affecting ~85% of threatened species). Climate change is the fastest-growing threat and may overtake habitat loss by mid-century, but it is not #1 yet.
❌ Confusing endangered and threatened: Endangered = at imminent risk of extinction throughout all or a significant portion of its range. Threatened = likely to BECOME endangered in the foreseeable future. Threatened is one step below endangered.
❌ Edge effects are always bad: Edge effects increase disturbance-tolerant species (which may look like "more biodiversity") but DECREASE interior-specialist species. More edge = more generalists, fewer sensitive species that need deep interior habitat.
A coastal marine ecosystem includes coral reefs, shellfish beds, and phytoplankton communities. Scientists have measured both rising ocean temperatures and declining ocean pH over the past three decades.
(a) Explain the chemical process by which increased atmospheric CO₂ leads to ocean acidification. Include the relevant chemical equation. (3 points)
(b) Describe how ocean acidification specifically threatens organisms that build calcium carbonate (CaCO₃) structures, and name TWO examples of such organisms. (3 points)
(c) Explain why coral reefs face a "double threat" from both ocean warming and ocean acidification, and describe how these two stressors interact. (3 points)
(b) Calcium Carbonate Organisms (3 pts): Acidification reduces the concentration of carbonate ions (CO₃²⁻) in seawater. Organisms that build shells or skeletons from calcium carbonate (CaCO₃) need these carbonate ions. With fewer available, shell-building becomes energetically costly and slower. In severely acidified conditions, existing CaCO₃ structures can actually dissolve. Examples: (1) Corals — build massive reef structures from CaCO₃; (2) Pteropods (sea butterflies) — planktonic mollusks with thin CaCO₃ shells that are critical food for salmon and other fish.
(c) Double Threat to Coral Reefs (3 pts): Ocean warming causes coral bleaching — when temperatures rise 1-2°C above the normal summer maximum, corals expel their symbiotic zooxanthellae algae, losing their color and up to 90% of their energy source. Simultaneously, ocean acidification weakens coral skeletons and slows new skeleton growth. The interaction is synergistic: heat-stressed corals are less able to repair acid-damaged skeletons, and weakened skeletons make corals more vulnerable to storm damage and bioerosion. Together, these stressors are projected to eliminate 70-90% of coral reefs at 1.5°C warming.
International environmental treaties have been used to address global environmental problems with varying degrees of success.
(a) Compare the Montreal Protocol and the Paris Agreement in terms of their targeted environmental problem, level of participation, and effectiveness. (4 points)
(b) Using the HIPPCO framework, identify and explain THREE specific threats to a population of polar bears in the Arctic. (3 points)
(c) Describe ONE in-situ and ONE ex-situ conservation strategy that could help protect an endangered species, and explain why in-situ conservation is generally preferred. (3 points)
(b) HIPPCO Threats to Polar Bears (3 pts — 1 each): (1) Habitat loss (H): Sea ice is the primary hunting platform for polar bears. Arctic warming is reducing sea ice extent and duration, shrinking available habitat for hunting seals. (2) Climate change (C): Rising temperatures are the root driver — Arctic amplification means the Arctic warms 2-3x faster than the global average, accelerating ice loss and altering the entire ecosystem polar bears depend on. (3) Pollution (P): Persistent organic pollutants (POPs) like PCBs bioaccumulate through the Arctic food chain, reaching high concentrations in top predators like polar bears, causing immune suppression and reproductive problems.
(c) Conservation Strategies (3 pts): In-situ (in habitat): Establishing marine protected areas and limiting industrial development in critical polar bear habitat, including denning areas and key sea ice corridors. This preserves the entire ecosystem and all species interactions. Ex-situ (out of habitat): Maintaining a captive breeding program in zoos with genetically managed populations as an insurance policy against wild population collapse. In-situ is preferred because it conserves the species within its natural ecosystem, maintains ecological relationships and behaviors, protects entire communities rather than single species, and allows natural selection to continue — ensuring long-term evolutionary viability.
Comprehensive Practice Questions
Mixed MCQ and FRQ in AP APES exam style. Attempt each before revealing the answer.
A student claims that "the hole in the ozone layer is causing global warming." Which of the following best corrects this misconception?
- (A) Ozone depletion and global warming are both caused by the same pollutants
- (B) Ozone depletion is caused by CFCs in the stratosphere, while global warming is caused by greenhouse gases trapping heat in the troposphere — they are separate problems
- (C) The ozone hole allows more heat to escape Earth's atmosphere, actually causing cooling
- (D) Global warming causes ozone depletion, not the other way around
Which of the following correctly pairs an environmental problem with its primary chemical mechanism?
- (A) Ocean acidification — CFCs react with seawater to form hydrochloric acid
- (B) Ozone depletion — CO₂ reacts with ozone in the stratosphere
- (C) Ocean acidification — CO₂ dissolves in seawater to form carbonic acid (H₂CO₃), lowering pH
- (D) Enhanced greenhouse effect — methane breaks down ozone, allowing more UV radiation through
Climate change is altering ecosystems worldwide, creating cascading effects on biodiversity.
(a) Explain how rising global temperatures can transform a native species' range into suitable habitat for an invasive species. Provide a specific example. (3 points)
(b) Using the concept of ecological tolerance, explain why specialist species (narrow tolerance ranges) are more vulnerable to climate change than generalist species. (2 points)
(c) Describe TWO ways that habitat fragmentation worsens the impact of climate change on biodiversity. (2 points)
(b) Specialist Vulnerability (2 pts): Specialist species have narrow tolerance ranges (stenothermal/stenohaline) for temperature, moisture, or other environmental factors. Even small climate shifts can push conditions outside their optimum zone into the zone of physiological stress or intolerance. Generalist species (wide tolerance, eurythermal) can tolerate a broader range of conditions, so equivalent climate shifts are more likely to remain within their tolerance limits. Example: coral reefs bleach at just 1-2°C above normal, while many weed species thrive across temperature ranges spanning 20°C or more.
(c) Fragmentation + Climate Change (2 pts — 1 each): (1) Fragmentation blocks migration corridors — as climate zones shift poleward, species need to move to track suitable conditions, but fragmented landscapes with roads, cities, and agricultural land prevent dispersal, trapping populations in warming habitat. (2) Fragmentation reduces population sizes and genetic diversity in isolated patches — smaller, genetically impoverished populations have less raw variation for natural selection to act on, reducing their capacity to adapt evolutionarily to changing climate conditions.
International cooperation has been essential for addressing global environmental problems.
(a) Explain why the Montreal Protocol is considered more successful than climate change agreements. Identify TWO specific factors that contributed to its success. (3 points)
(b) Describe the difference between the Endangered Species Act (ESA) and CITES in terms of scope and enforcement mechanism. (2 points)
(c) A critically endangered amphibian species is declining due to both habitat loss and a fungal disease (chytrid fungus) that is spreading to new regions due to climate change. Propose a conservation plan that addresses BOTH in-situ and ex-situ strategies. (3 points)
(b) ESA vs. CITES (2 pts): The Endangered Species Act (1973) is a US domestic law that prohibits the "take" (harm, harass, pursue, hunt, capture) of listed species within US jurisdiction and protects their critical habitat. It is enforced by US Fish and Wildlife Service with legal penalties. CITES (1975) is an international treaty that regulates cross-border trade in endangered species and their products. It operates through a permit system across 184 member countries but relies on each nation to enforce its provisions domestically, with varying levels of compliance.
(c) Dual Conservation Plan (3 pts): In-situ strategies: Protect and restore remaining habitat through legally designated reserves; create wildlife corridors connecting fragmented populations; implement biosecurity protocols to limit chytrid fungus spread (disinfecting boots, equipment); manage water bodies to maintain cool temperatures that slow fungal growth. Ex-situ strategies: Establish captive breeding colonies ("assurance populations") in disease-free facilities at zoos or research institutions; maintain a cryopreserved genetic bank (frozen sperm/eggs) to preserve genetic diversity; develop probiotic skin treatments in lab settings that can be tested and eventually applied to wild populations. Both approaches are needed because in-situ conserves the ecosystem context while ex-situ provides insurance against catastrophic population collapse from the spreading disease.
High-Frequency Common Mistakes — Full Unit 9
- 🌡️Greenhouse effect is natural and necessaryThe natural greenhouse effect keeps Earth at +15°C instead of -18°C. The ENHANCED greenhouse effect from human-added GHGs is the problem. Never say "the greenhouse effect is bad."
- 🏭CO₂ vs. CH₄ — total forcing vs. per-molecule potencyCH₄ has 28-36x higher GWP per molecule, but CO₂ is the most important anthropogenic GHG because it is emitted in vastly larger quantities and persists for 300-1,000 years.
- 🛡️Ozone depletion ≠ climate changeOzone depletion: CFCs, stratosphere, UV-B radiation problem, Montreal Protocol. Climate change: GHGs, troposphere, heat-trapping problem, Paris Agreement. Different causes, different layers, different treaties.
- 🌊Ocean is becoming "more acidic," NOT "acidic"Ocean pH has dropped from ~8.2 to ~8.1 — still basic (above pH 7). "Acidification" means moving toward the acidic end of the scale, not that the ocean has become an acid. Also: 0.1 pH drop = 30% more H⁺ ions (logarithmic scale).
- 🧊Sea level rise: thermal expansion AND ice meltBoth contribute — thermal expansion of warming water accounts for ~40% of current rise. Students commonly forget thermal expansion and attribute all sea level rise to melting ice alone.
- 📋Montreal Protocol ≠ Kyoto Protocol ≠ Paris AgreementMontreal (1987) = ozone, legally binding, huge success. Kyoto (1997) = climate, binding targets for developed nations only, limited success. Paris (2015) = climate, voluntary NDCs, all nations, insufficient progress so far.
- 🐍Invasive species lack predators, not "superior genes"Invasive species thrive in new environments because they are released from natural predators, diseases, and competitors — not because they are inherently "better" organisms. In their native range, they are kept in balance.
- 🦎Endangered vs. Threatened — know the differenceEndangered = imminent extinction risk. Threatened = likely to become endangered. The ESA lists both categories with legal protections, but endangered status triggers stronger restrictions.
- 🌿Habitat loss is STILL #1 — not climate change (yet)Habitat loss/fragmentation currently causes ~85% of species declines. Climate change is the fastest-growing threat and may overtake habitat loss by mid-century, but it is not the leading cause today.
- 🔄Positive feedback ≠ "good" feedbackIn climate science, "positive" feedback means self-reinforcing/amplifying (ice-albedo, permafrost thaw). "Negative" feedback means self-correcting/stabilizing. Positive feedbacks accelerate warming — they are NOT beneficial.
- 📈Mitigation vs. Adaptation — don't mix them upMitigation addresses the CAUSE (reducing emissions: solar panels, EVs, reforestation). Adaptation addresses the EFFECTS (sea walls, drought-resistant crops, early warning systems). Both are needed simultaneously.
- 🐚Coral reefs face a double threatWarming causes bleaching (expelling zooxanthellae). Acidification weakens CaCO₃ skeletons. These interact synergistically — heat-stressed corals cannot repair acid-damaged structures. 70-90% of reefs projected lost at 1.5°C.
Unit 9 carries the highest exam weight at 15-20%. Prioritize: greenhouse effect mechanism and GHG comparison (Topic 9.3), positive feedback loops (Topic 9.4), mitigation vs. adaptation (Topic 9.5), ocean acidification chemistry (Topic 9.7), and HIPPCO framework (Topic 9.10). FRQs frequently ask you to compare international treaties, explain feedback mechanisms with diagrams, or connect multiple topics (e.g., how climate change drives invasive species expansion while fragmenting habitat). Always distinguish between ozone issues and climate issues — the exam tests this confusion directly.