Unit 9 – Global Change

Ozone Layer Functions

• UV Radiation Protection: Ozone absorbs UV-B (280-320 nm) and UV-C (<280 nm); protects organisms from DNA damage, cancer, cataracts, immune suppression
• UV-B Penetration: 1% ozone loss → 2% UV-B increase (nonlinear relationship); small ozone loss = significant health impact
• Temperature Regulation: Ozone absorption warms stratosphere; temperature inversion creates temperature maximum; affects atmospheric circulation patterns
• Natural Ozone Cycle: Formation: \(O_2 + UV \rightarrow O + O_3\) (Chapman cycle); destruction: \(O_3 + hv \rightarrow O_2 + O\); natural equilibrium maintains ~3 ppm ozone
• Natural Variability: Ozone fluctuates seasonally (up to ±10%); solar cycle affects UV production; volcanic aerosols affect ozone; baseline ~350 DU (Dobson units)

Ozone-Depleting Substances (ODS)

Protocol Evolution

• Original Protocol (1987): Required 50% CFC reduction by 1999; CFCs, halons, methyl bromide identified
• London Amendment (1990): Accelerated timeline; 100% CFC phase-out by 2000 (developed nations); added HCFCs, carbon tetrachloride
• Copenhagen Amendment (1992): Even faster phase-out (1994 advanced to 1996); added methyl bromide; tightened control measures
• Kigali Amendment (2016): Added HFCs (potent greenhouse gases); phase-down 85% by 2047; climate co-benefit (~0.4°C avoided warming by 2100)
• Compliance Rate: Exceptional (>99%); developed nations met early targets; developing nations given additional time (grace period to 2010-2030); voluntary leadership by many

Alternatives to Ozone-Depleting Substances

💡 Exam Tip: Montreal Protocol most successful environmental treaty (99.7% ODS phase-out). CFCs banned 1996 developed, 2010 developing. Alternatives: HCFCs (low ODP but transitional), HFCs (zero ozone depletion but GHG), HFOs (best, low GHG + zero ozone). Atmospheric CFCs declining ~1%/year; full recovery ~2070 (long residence time). Antarctic hole area peaked 2006; slow recovery. Kigali Amendment adds HFC phase-down (climate benefit). Know: timeline, alternatives, recovery projection, why successful (international cooperation + technology availability).

Radiative Balance and Earth's Energy

• Solar Energy Input: Sun provides ~1,361 W/m² at top of atmosphere (solar constant); Earth surface receives ~173 W/m² average (accounting for geometry, reflection)
• Radiative Balance Equation: \(Energy \, in = Energy \, out\) at equilibrium; incoming solar = outgoing infrared; any imbalance causes warming or cooling
• Solar Energy to Infrared: Sun emits visible/UV light; Earth absorbs; re-emits as infrared (heat) radiation
• Atmospheric Opacity: Visible light passes atmosphere; infrared trapped by GHGs; differential absorption creates warming
• Natural GHEs: Water vapor (~50% natural effect), CO₂ (~20%), methane (~9%), nitrous oxide (~5%), ozone (~3%), others (~13%); without these, Earth freezes
• Equilibrium Temperature: Without GHGs ~-18°C; with natural GHEs ~+15°C; human enhancement ~+1.1°C since pre-industrial (33°C + 1.1°C = 34.1°C total effect)

Greenhouse Gas Properties

• Infrared Absorption: GHGs have molecular bonds that absorb infrared photons; vibration modes active at IR wavelengths; gases with asymmetric molecules (CO₂, H₂O, CH₄) active; symmetric molecules (O₂, N₂) inactive
• Atmospheric Window: 8-14 μm infrared wavelengths transparent to atmosphere (window); GHGs don't fully block this region; partial transparency allows heat escape
• Back Radiation: GHGs re-emit absorbed IR in all directions (including back to surface); increases surface temperature; energy balance shifts upward
• Forcing Effect: Each GHG has radiative forcing value (W/m²); CO₂ ~1.7 W/m²; methane ~0.5 W/m²; total ~2.0 W/m² current imbalance
• Global Warming Potential (GWP): Relative potency of GHGs; CO₂ = 1 (reference); methane ~28-34x (over 100 years); nitrous oxide ~265-310x; SF₆ ~23,500x (extremely potent)
• Atmospheric Residence Time: CO₂ ~200-300 years; methane ~12 years; nitrous oxide ~114 years; longer residence = more cumulative impact; CO₂ most concerning long-term

Enhanced Greenhouse Effect

💡 Exam Tip: Natural GHE keeps Earth 33°C warmer (~-18°C → +15°C). Enhanced GHE from human emissions adds ~1.1°C (to +16.1°C actual). GHGs absorb IR; CO₂ most important long-term (300-year residence). Radiative forcing ~2.0 W/m² current imbalance. Atmospheric window (8-14 μm) partially transparent. Know: energy balance, back radiation, radiative forcing, residence times, GWP values. Don't confuse: natural (necessary) vs. enhanced (dangerous).

Primary CO₂ Sources

• Energy Sector (~70% of CO₂): Coal (40% of energy CO₂), oil (36%), natural gas (20%), other (4%); power generation, transportation, heating
• Coal Combustion: ~10 billion tonnes CO₂/year; dirtiest fuel; 100+ year coal power plants built; coal retirement slow despite climate urgency
• Oil Use: ~12 billion tonnes CO₂/year; transportation primary (90%); difficult to decarbonize (aviation, shipping lack alternatives)
• Natural Gas (~8 billion tonnes): Marketed as bridge fuel (lower than coal); but methane leakage during extraction/transport (2-7%) undermines climate benefit
• Industrial Processes (~10% of CO₂): Cement production (~8% global CO₂; decarbonization challenging); steel, chemicals, refining
• Deforestation (~10-15% of CO₂): Amazon clearing, tropical logging; releases stored carbon + reduces future carbon uptake
• Global Distribution: China ~28% of emissions (manufacturing hub, coal-dependent), USA 14%, EU 10%, India 7%, Russia 5%; developing nations' share increasing (industrialization)

Methane Emissions and Sources

• Global Methane ~800+ million tonnes CO₂-eq/year: ~28x CO₂ potency (100-year GWP); atmospheric concentration rising ~7-10 ppb/year (faster than CO₂)
• Agriculture (~50% of methane): Cattle (~30% of emissions; ruminant digestion produces CH₄), rice paddies (anaerobic bacteria), manure management; hard to reduce (global meat demand growing)
• Fossil Fuel Extraction (~30% of methane): Coal mining, oil/gas extraction, natural gas transport; leakage rates 2-7% of production (undermines climate benefits of gas)
• Waste (~20% of methane): Landfills, wastewater treatment, composting (anaerobic decomposition); ~15 year atmospheric lifetime (short vs. CO₂)
• Wetlands/Natural (~5-10%): Tropical wetlands, peatlands, permafrost (methane seeps); increasing with climate change (positive feedback)
• Reduction Opportunities: Methane easier to reduce than CO₂ (shorter lifetime); agricultural practices (feed additives, manure management), fossil fuel leak detection/repair, landfill gas capture; 30-45% reduction achievable

Nitrous Oxide and Other GHGs

• Nitrous Oxide (~310 million tonnes CO₂-eq): ~310x CO₂ potency (100-year GWP); ~114-year atmospheric lifetime (very persistent); concentration rising ~0.25% per year
• Agricultural Sources (~70% of N₂O): Fertilizer application (nitrogen conversion by soil bacteria); manure management; rice paddies; livestock systems
• Industrial Sources (~20% of N₂O): Adipic acid production (nylon manufacture), nitric acid production (fertilizer); wastewater treatment
• Natural Sources (~10% of N₂O): Soil nitrification/denitrification, ocean microbial processes; increasing with climate change
• Other GHGs: Sulfur hexafluoride (SF₆, 23,500x CO₂), hydrofluorocarbons (HFCs, 100-1,000x CO₂), perfluorocarbons (very potent); industrial use; replacement compounds being developed
• Combined Forcing: CO₂ ~60% of radiative forcing, CH₄ ~20%, N₂O ~6%, others ~14%; CO₂ dominates long-term (persistence)

Atmospheric Accumulation and Keeling Curve

• Net Accumulation: Emissions ~40 ppm CO₂/year equivalent; atmospheric increase ~2.5 ppm/year; difference absorbed by sinks (~37 ppm/year)
• Carbon Sinks Saturation: Ocean absorbs ~25% (~10 ppm/year); land absorbs ~25%; saturation rates may increase (negative feedback at higher CO₂?) or decrease (positive feedback)
• Keeling Curve (Mauna Loa): Continuous CO₂ measurement since 1958; shows seasonal oscillation (~2.5 ppm range) + long-term trend (2 ppm/year average)
• Seasonal Cycle Reason: Northern Hemisphere vegetation dominates (vegetated area 2x southern); summer growth absorbs CO₂ (minimum August), winter decomposition releases (maximum May)
• Amplitude Increase: Seasonal swing ~1 ppm (1958) → ~2.5 ppm (2024); indicates stronger seasonal uptake or faster decay
• Stabilization Scenarios: 550 ppm scenario (business-as-usual ~2050-2070); 450 ppm requires ~70% emissions reduction NOW; Paris 1.5°C target requires immediate peak + rapid decline
• Carbon Budget Concept: Each 0.1°C warming uses ~40 ppm CO₂ equivalent carbon budget; 1.5°C target = 400-430 ppm CO₂ ceiling; 2°C target = 500-550 ppm; overshoot possible with later drawdown

💡 Exam Tip: CO₂ ~37 Gt/year emissions; 50% absorbed sinks, 50% accumulates (~2.5 ppm/year). Sources: coal 40%, oil 36%, gas 20%, industry 10%, deforestation 10-15%. CH₄ ~800M tonnes CO₂-eq (28x CO₂); 50% agriculture, 30% fossil fuels, 20% waste. N₂O ~310M tonnes CO₂-eq (310x CO₂); 70% agriculture. Keeling Curve shows seasonal cycle + long-term upward trend. Know: sources, atmospheric residence times, radiative forcing, sink rates, future scenarios (550 ppm vs. 450 ppm targets).

Temperature Distribution

• Unequal Warming: Land warming ~2x ocean (0.25°C/decade land vs. 0.12°C/decade ocean); Arctic warming 3-4x global average (Arctic amplification); high mountains warming faster than sea level
• Seasonal Variation: Winter warming faster than summer (~2.5x in many regions); nights warming faster than days (urban heat island effect amplifies)
• Regional Patterns: Some regions warming >2°C (Arctic, high mountains, land interiors); ocean basins warming 0.5-1.5°C; slowdown regions (e.g., North Atlantic temporary cooling)
• Daily Temperature Changes: Diurnal range (max-min) declining; nights warming faster; fewer frost days; growing season extended 1-2 weeks in many regions
• Record Breaking Acceleration: Temperature records broken every 2-3 years (1998, 2005, 2010, 2016, 2020, 2023); acceleration indicates not natural variability but forced warming

Extreme Weather Events

• Heat Waves: Frequency increasing 2-3x per decade; duration lengthening (single events now 20-30 days); intensity breaking records; mortality increasing (elderly, outdoor workers vulnerable)
• Wet-Bulb Temperature Threshold: Combination heat + humidity can exceed human tolerance (~35°C wet-bulb); approaching limits in Persian Gulf, South Asia; outdoor work becomes impossible
• Cold Extremes Declining: Frost days decreasing; bitter cold events rarer; when they occur, sometimes more intense (polar vortex displacement)
• Precipitation Intensification: Heavy rain events more frequent; hourly intensity increasing 5-10%/°C warming (warmer atmosphere holds 7% more water); flooding risks rising
• Drought Intensification: Some regions drying (Mediterranean, Southwest USA, Amazon); soil moisture decreasing; water stress increasing; wildfires more frequent/severe
• Hurricane/Typhoon Intensity: Peak intensity category storms increasing; rainfall totals rising; storm motion slowing (longer duration impacts); model projections show 1-10% wind speed increase; 10-20% rainfall increase per °C
• Attribution Science: Climate models now enable linking specific extreme events to human influence; 2023 heat waves have 50%+ probability attributable to climate change (vs. ~5% pre-industrial baseline)
• Economic Costs Escalating: Extreme weather damage ~$300+ billion/year currently; increasing ~10%/year; insurance industry stressed; uninsurable events emerging

Precipitation and Hydrological Changes

• Global Precipitation Increase: ~2% increase per °C warming (more water in warmer atmosphere); but distribution uneven (wet regions wetter, dry drier)
• Regional Patterns: Tropical regions generally wetter (increased ITCZ convection); Mediterranean, Southwest USA, Amazon becoming drier; monsoon patterns shifting; uncertainty in magnitude
• Snowfall Decline: Mountain snowpack declining 10-30% per °C (earlier melt, less accumulation); hydrological drought even if precipitation unchanged (snow storage disappears)
• Groundwater Depletion: Aquifers over-extracted (Ogallala, Indo-Gangetic); climate change reducing recharge rates; water stress intensifying
• River Flow Alterations: Spring/early summer peak flows declining (snowmelt earlier/reduced); late summer/fall flows decreasing (reduced glaciers); species migration timing mismatches
• Water Security Crisis: 2+ billion people face water stress currently; climate change adding ~200-400 million; competition for water increasing (agriculture, industry, human use)

Arctic Amplification and Feedback Loops

• Arctic Warming 3-4x Global: Caused by ice-albedo feedback (white ice/snow melts → dark ocean exposed → more solar absorption); also lapse-rate feedback (temperature gradient changes)
• Sea Ice Decline: Arctic sea ice declining ~13% per decade; September minimum ice ~40% loss since 1979; could be ice-free summers by 2030s (even with Paris targets)
• Permafrost Thaw: Active layer deepening; permafrost disappearing; releases methane/carbon (methane burst possible); methane hydrate feedback risk (abrupt warming)
• Greenland Ice Sheet: Accelerating mass loss ~270 billion tonnes/year (increasing rate); contributed ~0.7 mm/year sea level rise currently; if fully melted = 7 m sea level rise (10,000 years at current rates)
• Positive Feedbacks (Warming): Water vapor (+1.8 W/m²/°C), ice-albedo (+0.3 W/m²/°C), cloud-radiation (±0.5 W/m²/°C, uncertain), biological (0-0.2 W/m²/°C); total feedback ~3 W/m²/°C (amplifies warming 2-3x)
• Climate Sensitivity Implications: Initial 1°C from 2xCO₂ → feedbacks add 2-3°C → total 3°C (range 1.5-4.5°C); tipping point risk >2°C (runaway warming)

💡 Exam Tip: 1.1°C warming so far; 2023 hottest year. Arctic warming 3-4x (ice-albedo feedback). Land 2x ocean. Winter faster than summer. Extreme heat/rain/drought intensifying. Precipitation +2%/°C global (but uneven distribution). Snowpack declining 10-30%/°C. Permafrost thawing (methane feedback). Positive feedbacks amplify warming 2-3x. Climate sensitivity ~3°C per doubling CO₂. Know: feedback mechanisms, regional patterns, extreme event attribution, hydrological changes, Arctic amplification.

Thermal Profile and Stratification

• Warming Distribution: Surface 0-100 m warming fastest (~0.18°C/decade); upper ocean (100-300 m) warming ~0.12°C/decade; deep ocean (>3000 m) warming ~0.001°C/decade (very slow)
• Thermal Stratification Increasing: Surface warms faster than depth; density gradient steepens; mixing declines; oxygen delivery to deep water impaired; nutrient cycling disrupted
• Thermocline Depth: Top of thermocline shoaling (rising ~1 meter per year regionally); affects upwelling zones, reduces nutrient delivery
• Thermal Expansion Component: Accounts for ~30% of sea level rise (rest from ice melt); density change ~0.2 kg/m³ per °C warming; significant volume change
• Committed Warming: Ocean thermal lag ~100-300 years; even if atmosphere stabilized, ocean would continue warming (continue sea level rise ~100+ years)

Marine Heat Waves

• Definition: Discrete warm water masses; threshold-based (>90th percentile temperature for 5+ days); or anomaly-based (>1.5°C above baseline)
• Frequency Increase: 50% increase in frequency since 1982; 17% increase in duration; 0.1°C per decade increase in intensity; 2023 exceptional marine heat waves globally
• Ecosystem Impacts: Coral bleaching (>1-1.5°C above seasonal normal); kelp forest collapse (sea urchin population explosion); fish migration (prey moving northward); seabird/marine mammal starvation
• Persistence:** Some marine heat waves lasting 100+ days; 2023 Pacific marine heat wave disrupted fisheries, food webs; 2016 event caused ~$1 billion in economic losses
• Compounding Stressors: Heat wave + acidification + deoxygenation creates perfect storm; ecosystem collapse risk when multiple stressors combine
• Predictability: Heat waves becoming more predictable; seasonal forecasts improving; early warning systems enabling adaptation (fisheries management, conservation action)

Deoxygenation and Dead Zones

• Oxygen Depletion Mechanisms: Warm water holds 20% less oxygen per °C warming; stratification reduces mixing/ventilation; microbial respiration depletes remaining oxygen
• Oxygen Minimum Zones (OMZs): Expanding globally; shoaling at 1-2 m per year; suboxic/anoxic conditions; ~400 dead zones globally, expanding ~2% per year
• Hypoxia Definition: <2 mg O₂/L = hypoxic (fish avoidance); <0.5 mg/L = anoxic (only anaerobes); most fish < 1 mg/L
• Habitat Compression: Hypoxic water squeezes fish into narrow oxygen-rich surface layer; predator concentration increases; vulnerability to fishing; shallow mixed layer = easy catch
• Microbiome Changes: Anaerobic bacteria dominate OMZs; methane/hydrogen sulfide production; different nutrient cycling; ecosystem function fundamentally altered
• Human Impact: Fisheries production threatened; food security risk for coastal populations (1+ billion depend on fish); aquaculture vulnerable

Ocean Circulation Changes

• Thermohaline Circulation Slowdown: Atlantic Meridional Overturning Circulation (AMOC, "conveyor belt") weakened ~15% since 1950s; freshwater input (Greenland melt) reduces density gradient; projections 20-50% weakening by 2100
• Potential Collapse Threshold: Tipping point estimate ~2°C warming (5-10 year transition possible); would dramatically alter regional climates (Europe cooling paradoxically while global warming)
• Upwelling Changes: Some regions intensifying (Peru, parts of West Africa); others weakening (Mediterranean); affects nutrient delivery, fisheries productivity, local weather
• Coastal Currents Altered: California Current, Kuroshio Current, others all showing changes; affect marine heat distribution, cold-water ecosystem support
• Impacts on Climate: AMOC weakening could slow Atlantic warming (regional); but global warming continues; unequal distribution risks (some regions protected temporarily, others accelerate)

💡 Exam Tip: Ocean absorbs 90% excess heat; warming ~0.13°C/decade surface. Thermal expansion contributes 30% sea level rise. Stratification increasing (warm surface, cold deep). Marine heat waves frequency +50%, duration +17%, intensity increasing. Deoxygenation expanding ~400 dead zones; OMZs shoaling 1-2 m/year. AMOC weakening 15% (tipping point risk ~2°C). Know: heat content distribution, thermal lag, marine heat wave impacts, dead zone expansion, circulation changes, fisheries implications.

Chemical Reactions and pH Scale

• CO₂ Dissolution: \(CO_2 + H_2O \rightarrow H_2CO_3 \rightarrow H^+ + HCO_3^- \rightarrow 2H^+ + CO_3^{2-}\); equilibrium shifts as CO₂ increases; more H⁺ (acidic) and fewer CO₃²⁻ (carbonate)
• pH Definition: \(pH = -\log[H^+]\); ocean pH 8.2 (1750) → 8.1 (2024) = 0.1 unit drop; logarithmic scale so 0.1 pH = 26% H⁺ increase (actually ~30%)
• Carbonate System Equilibrium: Higher CO₂ drives equilibrium right; [HCO₃⁻] increases, [CO₃²⁻] decreases; both effects reduce carbonate saturation state
• Saturation State (Ω): Ratio [Ca²⁺][CO₃²⁻]/Ksp; Ω=1 saturation horizon (equilibrium); Ω<1 undersaturation (shells dissolve); pre-industrial Ω~4.8 surface, ~0.5 deep; current Ω~4.0 surface, <0.5 deep
• Future Projections: By 2100, surface Ω could drop to 2-3 (mild suppression); depth Ω<0.5 extends shallower (saturation horizon shoals); worst-case scenarios Ω~1 even at surface

Saturation Horizon and Vulnerable Organisms

• Saturation Horizon Definition: Depth where water transitions from supersaturated (Ω>1) to undersaturated (Ω<1); shells dissolve below this depth; horizon currently 500-1,000 m Pacific
• Shoaling Rate: ~1-3 m/year shallowing in many regions; projected another 100-300 m by 2100; corals, pteropods, planktonic foraminifera may enter undersaturated waters
• Pteropods (Sea Butterflies): Planktonic gastropods; fragile aragonite shells; live near surface; already experiencing shell dissolution in undersaturated waters; decline cascades (food for seabirds, fish)
• Corals: Require Ω>3 for calcification; many species at Ω~3-4 currently; reduced calcification rate; weaker skeletons; more susceptible to damage/breakage
• Oysters and Clams: Larvae most sensitive; shell deformation at pH<8.0; hatchery failures documented (Pacific oyster, clam); economic impact ~$1+ billion/year increasing
• Echinoderms (Sea Stars, Urchins): High-Mg calcite shells more soluble; very sensitive to acidification; larval development disrupted
• Food Web Impacts: Pteropod decline → seabird (kittiwake, puffin) starvation; salmon decline → killer whale populations crash (documented 1990s); trophic cascades

Physiological and Ecological Effects

• Calcification Suppression: Rates decrease 10-50% depending on species/pH; metabolic cost of calcification increases (more energy needed to concentrate carbonate); growth stunted
• Dissolution of Existing Shells: Pteropods, foraminifera dissolving in undersaturated waters; visible pitting observed; impacts on shell integrity, buoyancy
• Behavioral Changes: Fish larvae sensory disruption (olfaction impaired by acidification); settlement cues confused; larvae can't find suitable habitat; recruitment failure
• Metabolic Acidosis: Body fluid pH regulation requires energy; acidosis stress response triggered; immune suppression, reduced growth, behavioral changes
• Developmental Delays: Larval development slowed; metamorphosis delayed; timing mismatch with food availability; survival rates reduced
• Genotypic Variation: Some populations showing tolerance evolution (rapid selection); but cannot evolve fast enough to match acidification rate
• Ecosystem Restructuring: Acidification-tolerant species (jellyfish, nudibranchs) expanding; native species declining; food web rewiring; ecosystem function altered

Economic and Food Security Impacts

• Shellfish Industry Vulnerability: Hatchery failures, growth reduction, quality decline; ~$1+ billion annual economic impact increasing; insurance difficult (climate change not traditionally covered)
• Wild Fisheries at Risk: Key species (salmon, cod, small pelagics) dependent on pteropod/zooplankton food web; population declines cascade; commercial fisheries decline
• Food Security Threat: 1+ billion people depend on fish for protein; 50+ countries >50% animal protein from seafood; acidification threatens food security for poorest populations
• Mitigation/Adaptation: Aquaculture water treatment (buffering), selective breeding, hatchery management; but limited scalability; ultimately requires CO₂ reduction
• Justice Concerns: Developed nations high-emission responsibility; developing nations bearing disproportionate food security consequences; equity considerations essential

💡 Exam Tip: Ocean pH 8.2 → 8.1 (0.1 unit drop = 30% H⁺ increase). CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻. Carbonate [CO₃²⁻] decreases. Saturation horizon (Ω=1) shoaling 1-3 m/year. Pteropods dissolving, oyster larvae failing, coral calcification suppressed. Know: chemistry equations, pH scale, saturation state, vulnerable organisms, food web impacts, economic costs ($1B+/year shellfish), food security threat for coastal populations.

Introduction Mechanisms

• International Trade: ~10+ billion tonnes cargo shipped annually; shipping ballast water (billions of liters) transfers species 1000s km; ballast sediments contain eggs/larvae; aquaculture escapes common
• Pet/Garden Trade: Escaped animals/plants; aquarium fish introductions (lionfish Atlantic), garden plants (kudzu, giant hogweed), pet reptiles (pythons Everglades)
• Accidental Transport: Hitchhiking on cargo, vehicles, clothing; seeds in soil/packing; insects in imported produce; difficult to prevent without intensive inspection
• Deliberate Introduction: Ill-conceived biocontrol attempts; game species releases; aesthetic reasons; sometimes become invasive (cane toads Australia, rabbit Australia, boar North America)
• Climate-Mediated Range Expansion: Species not intentionally introduced but spreading from neighboring invaded regions; warming enables poleward/upslope migration; Asian giant hornets, lionfish expanding northward

Establishment Factors and Success

• Lack Natural Enemies: Predators/parasites left behind; enemy release hypothesis; predation pressure dramatically reduced; exponential population growth possible
• Competitive Superiority: Often outcompete natives; faster growth, better resource acquisition, aggressive behavior; natives can't compete; exclusion common
• Phenotypic Plasticity: Adaptability to new environment; tolerance to local conditions; rapid evolution possible (thousands of generations per decade)
• Rapid Reproduction: Short generation time, high fecundity; population doubling weekly/monthly; overwhelming native predators/competitors through sheer numbers
• Allee Effect Absence: No minimum population threshold for success; unlike natives, tiny populations can establish; propagule pressure matters; more release attempts = higher colonization probability
• Disturbance Advantage: Invaded ecosystems often disturbed (human activity); competitive vacuum from disturbance; invasives colonize first; excludes natives attempting recovery

Ecological and Economic Impacts

• Famous Examples: Zebra mussels (block pipes, 1990s invasion Great Lakes, still spreading), kudzu (smothers plants, 1+ million acres), cane toads (Australia, no predators, spreading), lionfish (Atlantic, predates natives, population explosion), rabbits (Australia, no predators, plague)
• Predation on Natives: Lionfish eating 90% of native fish biomass locally; invasive snails eating endemic snails (extinction); introduced predators causing native population crashes
• Competition and Exclusion: Invasive shrubs outshading natives; aggressive vines monopolizing light; invasive grasses altering fire regimes
• Habitat Modification: Invasive earthworms altering soil carbon cycling; invasive trees changing forest structure; beavers (in Europe, introduced) flooding habitats; ecosystem function fundamentally altered
• Disease Transmission: Invasive species carrying new pathogens; fungal diseases (white-nose syndrome bats), parasites (bobtail disease sea stars), viruses
• Hybridization: Invasive species interbreeding with natives; genetic swamping; endemic species loss (endangered species + invasive congener = extinction)
• Economic Cost: ~$1 trillion/year global damage (agriculture $220B, forestry $40B, fisheries $50B, infrastructure $1.3T); medical/health costs from invasive parasites/vectors
• Irreversibility: Once established, nearly impossible eradicate; control expensive, ongoing; early detection/rapid response only effective approach

Prevention and Management

• Prevention Most Effective: Biosecurity regulations, ballast water treatment (heat, UV, chemical), inspection protocols, quarantine systems; developing nations less regulated (risk)
• Early Detection/Rapid Response: Small populations eradicable; delay = explosion; monitoring essential (invasive species often detected too late)
• Eradication Attempts: Success rate <10% after establishment; cost prohibitive for large areas; isolated islands only practical (Galapagos, New Zealand programs)
• Biological Control: Introduce natural enemy; risks secondary invasion; can backfire (classic example: cane toads introduced to control beetles, became plague)
• Chemical/Mechanical Control: Ongoing expense; temporary (herbicide, traps); population rebounds if management stops; long-term commitment required
• Habitat Restoration: Restore native communities; competitive advantage to natives; can exclude invasives; but slow, expensive
• Climate Change Interaction: Warming enables invasive range expansion; prevents native adaptation; invasives may thrive where warming stress makes natives vulnerable; future invasive pressure increasing

💡 Exam Tip: Invasive species 2nd extinction cause (after habitat loss). Introduction vectors: ballast water, pet trade, accidental transport. Success factors: no predators, competitive advantage, rapid reproduction. Examples: zebra mussels, kudzu, cane toads, lionfish. Economic cost $1T/year. Prevention only effective (eradication <10% success). Early detection/rapid response critical. Control methods: biosecurity, habitat restoration, biological control (risky). Climate change enabling poleward expansion. Know: examples, impacts, why invasives succeed, management strategies.

IUCN Conservation Status Categories

• Extinct (EX): No individuals remain; confirmed gone; dodo, Baiji dolphin, Pyrenean ibex (extinct 2000; de-extinction attempt using cloning)
• Extinct in the Wild (EW): Only exist in captivity/cultivation; cannot survive without human management; Arabian oryx (extinct 1972, reintroduced successfully), California condor
• Critically Endangered (CR): Extremely high extinction risk; <10 years to extinction if no intervention; <250 individuals typical; Sumatran rhino (~80), vaquita porpoise (~10), Javan rhino (~70)
• Endangered (EN): High extinction risk; population 250-2,500 typical; giant panda (recovered to 1,800+ from <1,000), black-footed ferret (reintroduction ongoing)
• Vulnerable (VU): Moderate risk; population 2,500-10,000; includes species like African elephants, sea turtles, polar bears
• Near Threatened (NT): May approach threatened category soon; 10,000-100,000 individuals; monitoring recommended
• Least Concern (LC): Large population, wide distribution; no current threat; most species in this category

Extinction Causes and Risk Factors

• Primary Causes (by %): Habitat loss 85%, overexploitation 10%, invasive species 5%, pollution 3%, other 2%; usually combined (multiple threats)
• Small Population Genetics: Inbreeding depression (loss of fitness); genetic drift (random allele loss); heterozygosity declining 1-5% per generation; minimum viable population estimate 500-5,000
• Stochastic Extinction: Random events (disease outbreak, drought, predator boom) can wipe out small populations; deterministic models inadequate
• Allee Effect: Reduced fitness at low population density; difficulty finding mates, reduced predator avoidance, lower foraging efficiency; extinction vortex once population below critical threshold
• Phenological Mismatch: Climate change shifting food availability timing; migratory birds arriving too early/late; breeding cycle mismatched with food peak; reproductive failure increasing
• Synergistic Stressors: Habitat loss + climate change + pollution = collapse; single factor manageable but combination catastrophic; ecosystem buffering capacity exceeded

Conservation Success Stories

• California Condor: Down to 27 individuals (1987); captive breeding program; now 500+ with half in wild; longest-lived bird (~80 years); future dependent on condor exposure to lead ammunition removal
• Arabian Oryx: Hunted to extinction in wild (1972); "Operation Oryx" captive breeding; reintroduced 1982; now 1,000+ wild; only species recover from near-total extinction in wild
• Giant Panda: Habitat protection, breeding programs; population 1,000 (1975) → 2,000 (current); delisted from Endangered to Vulnerable (2016); still dependent on protection
• Gray Whale: Harvesting ban (1966); population recovered ~20,000 (from ~5,000); delisted from Endangered; whaling alternative species still threatened
• Black-footed Ferret: Thought extinct 1979; rediscovered 1981 (Wyoming); captive breeding established; reintroduction ongoing; depends on prairie dog management (prey species)
• Lessons from Success: All required: legal protection, habitat restoration, breeding programs if necessary, international cooperation, funding commitment, monitoring; recovery takes decades; requires long-term vision

Conservation Strategies

• Habitat Protection/Restoration: Most important (~80% success factor); National Parks, private reserves, land trusts; restoration recovery slow (decades-centuries)
• Legal Protection: Endangered Species Act (USA), CITES (international), national laws; enables enforcement against poaching, habitat destruction; compliance variable
• Captive Breeding/Reintroduction: Last resort; expensive; success dependent on habitat availability; genetic management essential (avoid inbreeding)
• Wildlife Corridors: Connect fragmented habitats; allow gene flow, population mixing; require substantial land commitment; controversial (development prevention)
• Population Management: Translocations, genetic rescue (outcrossing with related populations), selective breeding; experimental, mixed results
• Community Engagement: Local support essential; economic incentives (ecotourism, payment for conservation); indigenous land management often effective
• Funding Challenge: Global conservation budget ~$20-30 billion/year; need $300+ billion/year for comprehensive protection; massive funding gap; priorities difficult

💡 Exam Tip: 41,000 species threatened; ~100-1,000x extinction rate. IUCN categories: Extinct, Extinct in Wild, Critically Endangered (<250 usually), Endangered, Vulnerable, Near Threatened, Least Concern. Extinction causes: 85% habitat loss, 10% overexploitation, 5% invasive species. Small population genetics: inbreeding, genetic drift, minimum viable population 500-5,000. Success stories: California condor, Arabian oryx, giant panda (recovery possible but rare). Know: IUCN classifications, risk factors, conservation strategies (habitat protection primary), examples, recovery timescales (decades+).

Population and Species Decline Metrics

• Living Planet Index (LPI): Tracks 32,000+ populations of 5,000+ vertebrate species; ~68% decline average; freshwater ecosystems worst (~83% decline); marine ~42%; terrestrial ~69%
• Regional Variation: Tropics worse (75% decline); Arctic 20-30% decline; temperate variable (some recovery after protection, but recovery incomplete)
• Extinction Rate Acceleration: Background extinction ~0.1-1 per million species/year; current rate 100-1,000 per million/year; 100-10,000x faster than natural; sixth mass extinction confirmed
• Previous Mass Extinctions: "Big Five" + human-caused: End-Ordovician, Late Devonian, End-Permian (90% species loss), End-Triassic, K/T (dinosaurs); current event comparable in rate/scale
• Recovery Timeline: Previous mass extinctions took 5-10 million years recovery; does current trajectory suggest we're causing another "Big One"?
• Species Threatened Count: ~41,000 species formally assessed as threatened; actual threatened likely higher (10+ million species described, most not assessed)

Primary Extinction Drivers

• Habitat Destruction (~85% of threat): Tropical forest loss (~1% per year), wetland drainage (87% lost historically), grassland conversion (40% converted), marine habitat destruction (bottom trawling, dredging)
• Habitat Fragmentation: Remaining habitat broken into isolated patches; connectivity lost; species can't migrate; small populations vulnerable to extinction
• Overexploitation (~10% of threat): Overfishing (35% stocks overexploited), poaching (elephants, rhinos, tigers), unsustainable logging, wildlife trade (~5+ billion animals traded annually)
• Invasive Species (~5% of threat): Second-leading extinction cause; established invasives almost impossible to eradicate; prevention critical; ~1 trillion/year cost
• Pollution (~3% of threat): Chemical contamination, plastic pollution, light pollution, noise pollution; chronic stress compounding other pressures
• Climate Change (Emerging Major Threat): Rapid environmental change exceeding species adaptation capacity; species range shifts; phenological mismatches; marine ecosystem disruption; Arctic/mountain species particularly vulnerable
• Synergistic Interactions: Multiple stressors interact multiplicatively; species experiencing habitat loss + climate change + invasives + pollution = collapse; ecosystem buffering overwhelmed

Biodiversity Hotspots and Global Patterns

• Hotspot Concept: ~36 biodiversity hotspots contain 70% world's species in 2.4% of land; tropical-focused; highest species density/endemism
• Major Hotspots at Risk: Amazon rainforest (threatened deforestation, climate tipping point), Congo Basin, Borneo/Southeast Asia (palm oil conversion), Madagascar (endemic species, high threat), Mediterranean, Cape Floristic Region
• Tropical Forest Dominance: 50%+ species in tropical forests; 1% annual loss = 0.5% species loss per year if geographically random; extinction debt (species committed to extinction before actual loss)
• Marine Biodiversity Hotspots: Coral Triangle (35% reef fish species), cold-water seamounts, upwelling regions; threatened overfishing, ocean acidification, warming
• Freshwater Biodiversity Crisis: 10% described species from ~0.01% water; extinction rate highest freshwater >marine>terrestrial; rivers/lakes 80+ year age < restoration capacity
• Unequal Distribution: Megadiverse developing nations (Brazil, Indonesia, Nigeria) home to majority species; conservation funding concentrated in developed nations; capacity/funding mismatch

Ecosystem Services and Economic Value

• Ecosystem Services Value: ~$125+ trillion annually in ecosystem services; biodiversity underpins: pollination ($500B-600B/year crops), water purification, climate regulation, food production, genetic resources
• Pollination Services: 75% crops dependent on animal pollinators; ~35% food production volume affected; pollinator decline (bees, butterflies) threatens food security
• Pharmaceutical Potential: 25% drugs derived from plants; most tropical species not screened; biodiversity loss = pharmaceutical potential loss
• Climate Regulation: Forests carbon sink 10+ billion tonnes CO₂/year; biodiversity enhances carbon storage; species loss = carbon release + reduced future uptake
• Genetic Diversity: Crop wild relatives maintain genetic diversity; climate change adaptation requires genetic variability; variety loss = breeding flexibility loss; famine risk increases
• Cultural Services: Spiritual significance, recreation, aesthetic value; indigenous lands highest biodiversity/lowest deforestation (~80% Amazon deforestation occurs outside indigenous territories)
• Economic Paradox: Biodiversity invaluable but unpriced; economic models ignore ecosystem service value; perverse incentives (convert forest to agriculture = GDP gain, but service loss not counted)

Solutions and Future Outlook

• Protected Area Expansion: Currently ~15% land, ~8% ocean protected; target 30-50% by 2050; requires political will + funding; indigenous land stewardship often most effective
• Habitat Restoration: 1+ billion hectares restoration potential; costs $1-10 trillion but returns ecosystem services; slow process (decades-centuries for full recovery)
• Sustainable Agriculture/Fisheries: Reduce environmental impact; compatible livelihoods; requires subsidy reform (currently $700+ billion/year agricultural subsidies encourage unsustainability)
• Climate Action: Limiting warming essential; >2°C warming = catastrophic biodiversity loss; renewable energy, forest protection, emissions reduction
• Invasive Species Prevention: Biosecurity, early detection/rapid response; treatment + prevention strategies
• Economic Transformation: Internalize ecosystem service costs; carbon pricing, biodiversity credits; payment for ecosystem services; circular economy principles
• Population Pressure: ~2 billion people live in high-biodiversity areas; alleviate through development, family planning, education; complex interactions with conservation
• Timeline Critical: Tipping points being crossed; if 1.5°C exceeded, ecosystem collapse risk spikes; action needed NOW not 2050; every species/hectare matters
• Hope Factor: Protected areas show recovery (some ecosystems ~20% population recovery post-protection); species reintroductions successful (Arabian oryx); restoration possible but requires resources + time; future not predetermined

💡 Exam Tip: 68% wildlife decline since 1970; 41k species threatened; 100-1,000x extinction rate (6th mass extinction). Primary drivers: 85% habitat loss, 10% overexploitation, 5% invasives, 3% pollution. 36 biodiversity hotspots = 70% species in 2.4% land. Ecosystem services $125T+/year (pollination, water, climate, food). Solutions: protected areas 30-50%, habitat restoration, climate action, sustainable agriculture, invasive prevention. Timeline critical; tipping points approaching. Know: Living Planet Index decline, hotspot locations, ecosystem service values, extinction drivers, recovery examples, future outlook.

✓ Comprehensive Coverage

• 9.1 Ozone depletion chemistry
• 9.2 Montreal Protocol success
• 9.3 Greenhouse effect mechanics
• 9.4 GHG emission sources
• 9.5 Climate change indicators
• 9.6 Ocean warming impacts
• 9.7 Ocean acidification chemistry
• 9.8 Invasive species ecology
• 9.9 Endangered species recovery
• 9.10 Biodiversity crisis scale

📊 Key Quantitative Data

• 420 ppm CO₂ (+50% 1750-2024)
• 1.1°C warming currently
• Antarctic ozone 50% depleted
• 99.7% ODS phase-out achieved
• Ocean pH 8.1 (↓0.1 since 1750)
• Thermal expansion +30% SLR
• 68% wildlife decline (1970-2024)
• 41k species threatened
• 100-1,000x extinction rate
• $125T ecosystem services/year