Free Unit Notes

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I. Stratospheric Ozone Depletion (Topic 9.1)

A. Protective ozone

1. Ozone (O₃) in the stratosphere absorbs much of the Sun’s harmful ultraviolet (UV) radiation before it reaches Earth’s surface.

2. UV can damage DNA. Increased UV exposure raises the risk of skin cancer and cataracts and can harm crops and phytoplankton.

3. UV splits oxygen molecules into oxygen atoms. These atoms combine with O₂ to form ozone; ozone absorbs UV and breaks apart again.

4. Stratospheric ozone protects life. Ground-level ozone is an air pollutant that damages lungs and plants.

B. Ozone destruction

1. Chlorofluorocarbons (CFCs) were used in refrigerants, aerosol propellants, and foams. Their stability allows them to reach the stratosphere.

2. UV breaks CFCs apart, releasing reactive chlorine atoms that destroy ozone. Bromine from halons, once used in fire suppression, also destroys ozone.

3. Chlorine is regenerated during the reactions, so one chlorine atom can destroy many ozone molecules.
   a. Cl + O₃ → ClO + O₂; then ClO + O → Cl + O₂.

C. Antarctic conditions

1. Extremely cold winters form polar stratospheric clouds. Reactions on their particles prepare chlorine compounds for rapid ozone destruction when spring sunlight returns.

2. The polar vortex, a ring of strong winds, isolates cold Antarctic air. Spring sunlight activates chlorine; later warming and air mixing help end the seasonal loss.

3. The ozone hole is severe seasonal thinning, not a completely empty opening. Natural seasonal conditions affect ozone loss, but human chemicals supply the excess chlorine and bromine.

II. Reducing Ozone Depletion (Topic 9.2)

A. Chemical replacements

1. Hydrofluorocarbons (HFCs) contain no chlorine and do not deplete stratospheric ozone. Many are strong greenhouse gases, so they can still increase warming.

2. Hydrochlorofluorocarbons (HCFCs) contain chlorine and still deplete ozone, although generally less than CFCs.

3. Other refrigerants include ammonia, carbon dioxide, and some hydrocarbons. Equipment must account for toxicity, pressure, flammability, and energy efficiency.

B. Preventing releases

1. The Montreal Protocol is an international agreement adopted in 1987 to phase out major ozone-depleting substances.

2. Repair leaks and recover refrigerants during servicing and disposal. Replacing equipment without recovering its refrigerant can release ozone-depleting chemicals.

3. Ozone recovery takes decades because many of these chemicals persist in the atmosphere for a long time.

III. The Greenhouse Effect (Topic 9.3)

A. Earth’s energy balance

1. Much incoming sunlight passes through the atmosphere. Earth absorbs some of this shortwave radiation and emits energy as longwave infrared radiation.

2. Greenhouse gases absorb outgoing infrared radiation and emit infrared in all directions, including toward the surface. This slows energy loss to space.

3. The natural greenhouse effect keeps Earth warm enough to support life. Adding greenhouse gases strengthens the effect and raises average temperature.

4. Ozone depletion and greenhouse warming involve different processes. The ozone hole is not the main cause of current global warming.

B. Principal gases and their sources

1. Carbon dioxide (CO₂) comes from fossil fuel burning, cement production, deforestation, respiration, and decomposition. Human activities add more than natural sinks remove.

2. Methane (CH₄) comes from livestock digestion, rice fields, landfills, wetlands, and leaks during fossil fuel production and transport.

3. Nitrous oxide (N₂O) comes mainly from microbial activity in soils and manure, including fertilized soils, and from some industrial activities.

4. CFCs and other fluorinated gases escape from cooling equipment and industrial products. CFCs contribute to both warming and ozone depletion.

5. Water vapor enters through evaporation and transpiration and leaves through condensation and precipitation. Its short atmospheric residence time prevents direct emissions from accumulating like CO₂.
   a. Water vapor remains an important feedback: warmer air can hold more moisture, which strengthens warming.

C. Comparing warming effects

1. Global warming potential (GWP) compares the warming from equal masses of gases over a stated period, often 100 years. CO₂ has a GWP of 1.

2. Among the gases emphasized here, many CFCs have the highest GWP, followed by N₂O, CH₄, and CO₂. Values depend on the gas and time period.

3. A gas’s overall climate effect also depends on how much is emitted and how long its effects persist. High GWP alone does not establish the largest total contribution.

4. CO₂ equivalent = mass of gas × GWP. With an assigned methane GWP of 28, 2 metric tons CH₄ represents 56 metric tons CO₂ equivalent.

IV. Increases in the Greenhouse Gases (Topic 9.4)

A. Atmospheric buildup

1. Burning fossil fuels transfers carbon from underground storage to the atmosphere. Deforestation releases stored carbon and reduces future CO₂ uptake by photosynthesis.

2. A carbon source releases more carbon than it absorbs. A carbon sink, such as a growing forest, absorbs more than it releases.

3. Atmospheric concentrations rise when inputs exceed removals. Slower growth in annual emissions does not necessarily stop this buildup.

4. Parts per million (ppm) measures concentration. For example, 420 ppm CO₂ means about 420 out of every million air molecules are CO₂.

B. Human and environmental impacts

1. Warming raises sea level through seawater expansion and melting land ice. Coastal flooding, erosion, saltwater intrusion, and storm-surge damage can displace people.

2. Disease vectors, such as mosquitoes and ticks, may expand toward higher latitudes or elevations as conditions warm. Disease spread also depends on rainfall, hosts, and prevention.

3. Heat waves, drought, floods, and changing food and water supplies can alter survival, reproduction, population distribution, and migration.

V. Global Climate Change (Topic 9.5)

A. Climate patterns and evidence

1. Weather describes short-term atmospheric conditions. Climate describes long-term patterns. Global warming is rising average temperature; climate change also includes shifts in rainfall, ice, and circulation.

2. Earth’s climate has changed throughout geologic time. Orbital changes, solar variation, volcanic activity, and atmospheric composition affect climate over different time scales.

3. Human greenhouse gas emissions are the dominant cause of modern long-term warming. Past natural changes do not establish the cause of current changes.

4. Ice cores contain trapped air that records past greenhouse gas concentrations. Ice isotope ratios help estimate past temperatures; tree rings, pollen, and sediments provide other climate evidence.

B. Interpreting measurements

1. A temperature anomaly is the difference from a reference-period average. An anomaly of +1.2°C means 1.2°C warmer than that average.

2. Percent change = [(new value − original value) ÷ original value] × 100. An increase from 280 to 420 ppm is 140 ppm, or 50%.

3. Average rate = change ÷ elapsed time. A 60 mm sea-level rise in 20 years averages 3 mm/year. Compare rates across intervals to identify acceleration.

C. Feedbacks and polar ecosystems

1. Albedo is the fraction of incoming sunlight reflected by a surface. Snow and ice reflect more than dark water or exposed land.

2. Warming melts ice, exposing darker surfaces that absorb more sunlight and cause further warming. This positive feedback amplifies change, especially in the Arctic.

3. Permafrost is ground frozen for at least two consecutive years. Thawing lets microbes decompose stored organic material, releasing CO₂ and, in oxygen-poor conditions, methane.

4. These gas releases strengthen warming and promote further thaw. Positive means the initial change is reinforced, not that the outcome is beneficial.

5. Sea-ice loss removes hunting, breeding, and feeding habitat. Polar bears, for example, lose ice platforms used to hunt seals.

D. Water, soil, and circulation

1. Warming increases evaporation. Where rainfall cannot replace lost moisture, soils dry and plants decline, leaving soil more exposed to erosion.

2. Intense rainfall increases runoff and soil loss. Changing temperature and moisture also affect decomposition, nutrient availability, and growing conditions.

3. Hadley cells move air between the equator and subtropics; the jet stream helps steer weather systems. Climate change can shift these patterns and regional rainfall.

4. Ocean currents redistribute heat. Thermohaline circulation depends partly on density differences caused by temperature and salinity.

5. Cold, salty water can sink. Warming and added freshwater can reduce density and weaken sinking, changing heat transport and regional climate.

E. Sea-level change

1. Thermal expansion means warming seawater takes up more space. Melting land glaciers and ice sheets also add water to the ocean.

2. Melting floating sea ice has little direct effect on sea level because it already displaces water. Its loss still reduces albedo and wildlife habitat.

3. Higher seas can create shallow-water habitat on flooded continental shelves, but can drown existing wetlands and coastal communities.

4. Some underwater communities may become too deep for sufficient sunlight. The photic zone is the upper water layer with enough light for photosynthesis.

5. Wetlands can move inland where space exists. Roads, buildings, and seawalls can block this movement.

F. Responses to climate change

1. Mitigation reduces causes: improve energy efficiency, replace fossil fuels with low-carbon energy, reduce methane leaks, and protect or restore carbon-storing ecosystems.

2. Adaptation reduces harm: improve flood planning, use heat-warning systems and drought-tolerant crops, restore wetlands, or relocate exposed buildings.

3. Solutions have tradeoffs. Seawalls may protect property while blocking wetland migration; forests can release stored carbon again if they burn or are cleared.

VI. Ocean Warming (Topic 9.6)

A. Heat and marine organisms

1. Extra greenhouse gases cause Earth to retain more energy. Oceans absorb much of the additional heat, and warming seawater expands.

2. Warming can alter metabolism, reproduction, survival, and species ranges. Some fish move toward cooler water, changing food webs and fisheries.

3. Warm water holds less dissolved oxygen than cold water under similar conditions. Greater metabolic demand can increase animals’ oxygen needs at the same time.

4. Stronger stratification, or separation into layers, can reduce mixing. Deep water receives less oxygen, and surface water may receive fewer nutrients.

B. Coral bleaching

1. Reef-building corals house photosynthetic algae that provide much of their food. Corals provide the algae with shelter and useful materials.

2. Heat stress can cause corals to lose algae or their pigments. The pale skeleton becomes visible through the tissue, producing coral bleaching.

3. A bleached coral is still alive but has lost a major food source. It may recover if stress ends or die if stress continues.

4. Reef decline removes feeding areas and shelter for other species. Reducing greenhouse gas emissions addresses warming; reducing local pollution and overfishing can improve reef resilience.

VII. Ocean Acidification (Topic 9.7)

A. Carbon dioxide and seawater chemistry

1. Ocean acidification is decreasing ocean pH, mainly from uptake of additional atmospheric CO₂ released by fossil fuel use, cement production, and deforestation.

2. Dissolved CO₂ reacts with water to form carbonic acid, which releases hydrogen ions: CO₂ + H₂O ⇌ H₂CO₃; H₂CO₃ ⇌ H⁺ + HCO₃⁻.

3. Extra hydrogen ions combine with carbonate ions: H⁺ + CO₃²⁻ ⇌ HCO₃⁻. This reduces carbonate available for building shells and skeletons.

4. Corals, shellfish, and some plankton use calcium and carbonate to form calcium carbonate: Ca²⁺ + CO₃²⁻ ⇌ CaCO₃.

5. Lower carbonate availability makes building and maintaining these structures harder. Under unfavorable chemical conditions, existing calcium carbonate can dissolve.

B. Interpreting pH and ecological effects

1. Acidification means becoming less basic; seawater does not need to fall below pH 7. A change from 8.2 to 8.1 is acidification even though both values are basic.

2. The pH scale is logarithmic. A one-unit pH decrease means ten times the hydrogen ion concentration; a two-unit decrease means 100 times as much.

3. For a pH decrease, the hydrogen ion concentration ratio is 10^(initial pH − final pH). A drop from 8.2 to 8.1 gives about 1.26 times as much, a 26% increase.

4. Losses of corals and shell-forming organisms can disrupt food webs, fisheries, and coastal protection.

5. Warming causes heat stress and bleaching; acidification changes seawater chemistry. Both can harm the same reef, and cutting CO₂ emissions addresses both causes.

VIII. Invasive Species (Topic 9.8)

A. Introduction and ecological harm

1. A native species occurs naturally in a region. A nonnative species has been moved outside its natural range. An invasive species establishes, spreads, and causes harm.

2. Many introduced species do not become invasive. Harmful invaders may outcompete native species, prey on them, spread disease, or change habitat and nutrient cycles.

3. Invaders may lack the predators, parasites, or diseases that limited them in their original habitat.

4. Many are generalists, able to use varied resources, and show r-selected traits, such as early reproduction and many offspring. These traits can support rapid population growth.

5. Humans transport species through ballast water, boat hulls, imported plants and goods, or released pets.
   a. Zebra mussels spread through water transport, clog pipes, and compete with native filter feeders.
   b. Kudzu shades other plants; introduced island rats consume native birds’ eggs and young.

B. Prevention and control

1. Inspections, quarantines, ballast-water treatment, and cleaning boats help prevent introduction. Early detection and rapid removal can prevent widespread establishment.

2. Mechanical control uses pulling, cutting, or trapping. It may disturb habitat and often requires repeated treatment.

3. Chemical control uses pesticides. Targeted application can reduce the invader but may also harm nontarget organisms.

4. Biological control uses a predator, parasite, or pathogen. Test it carefully because the control organism may harm native species or become invasive itself.

5. Combine suitable controls with native-habitat restoration and monitoring. Measure recovery of native species as well as reduction of invaders.

IX. Endangered Species (Topic 9.9)

A. Extinction risk

1. Extinction is the loss of a species everywhere. Extirpation is its disappearance from one area while it survives elsewhere.

2. In U.S. conservation terminology, an endangered species is in danger of extinction throughout all or a significant portion of its range. A threatened species is likely to become endangered in the foreseeable future.

3. Habitat loss, pollution, hunting, disease, invasive species, and competition can reduce populations. Competition can involve food, territory, breeding sites, or mates.

4. Specialists, species with small ranges or large territory needs, and slow-reproducing species are often especially vulnerable to environmental change.

5. Small populations are vulnerable to chance events and loss of genetic diversity. Inbreeding can expose harmful inherited traits and reduce survival or reproduction.

B. Environmental change and adaptation

1. A selective pressure affects survival and reproduction. Individuals with helpful inherited traits may leave more offspring, making those traits more common over generations.

2. Fitness means reproductive success. Populations evolve through natural selection; individuals do not develop needed inherited traits simply because they need them.

3. Some species move, change behavior, or adapt over generations. Others cannot keep pace because habitat is blocked, reproduction is slow, or useful genetic variation is limited.

C. Protecting populations

1. Protect habitat and migration routes, prevent poaching or illegal harvesting, limit unsustainable harvest, reduce pollution, and control invasive species.

2. The Endangered Species Act provides a U.S. framework for listed-species protection and recovery. CITES regulates international trade in listed wild species and their products.

3. Captive breeding can increase numbers, but reintroduction requires suitable habitat and control of the original threats.

4. Track population size, reproduction, survival, habitat quality, and genetic diversity. More individuals alone do not guarantee a self-sustaining population.

X. Human Impacts on Biodiversity (Topic 9.10)

A. Major human pressures

1. Biodiversity includes variation in genes, species, and ecosystems. It supports ecosystem services such as pollination, nutrient cycling, and water purification.

2. HIPPCO summarizes habitat destruction, invasive species, population growth, pollution, climate change, and overexploitation.

3. Population growth increases resource demand; consumption per person and technology also affect environmental impact.

4. Overexploitation removes organisms faster than populations replace them, as in overfishing and excessive wildlife harvesting.

5. Climate change shifts temperature, rainfall, and sea level, making some habitats unsuitable. Multiple pressures can reinforce one another.

B. Habitat fragmentation

1. Habitat fragmentation breaks large habitats into smaller, isolated patches. Roads, pipelines, agriculture, development, and logging cause fragmentation.

2. Isolation limits movement, access to mates, and gene flow, the transfer of inherited variation between populations. Roads can also kill crossing animals.

3. Edge effects are changes near habitat boundaries, including more sunlight, wind, predators, or invasive plants. These conditions may harm interior species.

4. Effects depend on the species. A road may block a small amphibian much more than a flying bird; wide-ranging species may need larger connected areas.

C. Domestication and genetic diversity

1. Domestication involves human breeding and management for useful traits. Examples include crops, livestock, and managed honeybee colonies.

2. Breeding a limited set of lines can reduce genetic diversity and leave many individuals vulnerable to the same disease or environmental change.

3. Preserve diverse varieties and breeds. Large numbers of one managed species do not replace the diversity of wild species, such as native pollinators.

D. Conserving biodiversity

1. Protected areas conserve habitat when protection is enforced. Large, connected reserves can support species that need extensive territory.

2. Habitat corridors connect patches, supporting movement, gene flow, and range shifts. Poorly planned corridors can also spread disease or invasive species.

3. Restoration repairs damaged ecosystems, such as by replanting native vegetation or restoring wetland water flow. It may not recreate all features of an intact ecosystem.

4. Sustainable land use limits unnecessary clearing, protects stream buffers, and keeps harvest within population replacement rates.

5. Reuse, repair, and recycling reduce some demand for extraction and disposal. They still require energy and do not eliminate every environmental impact.

6. Match conservation to the cause of decline and monitor results. A reserve alone may fail if the species cannot reach food, mates, or suitable habitat outside it.

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